2
THEME PHYSIOLOGY

OF HUMANS
AND ANIMALS

Chapter 8 Respiratory System in Humans
and Animals

Chapter 9  Nutrition and the Human
Digestive System

Chapter 10  Transport in Humans and Animals
Chapter 11  Immunity in Humans
Chapter 12  Coordination and Response in Humans
Chapter 13  Homeostasis and the Human Urinary System
Chapter 14  Support and Movements in Humans and Animals
Chapter 15  Sexual Reproduction, Development and Growth in Humans

and Animals

This theme aims to
provide an understanding of

the physiological processes in
humans and animals. This theme

focuses on physiological processes,
which are respiration, nutrition,

sensitivity, excretion, movement,
reproduction and growth as well

as cell division.
• What are the different respiratory structures found in:
 • insects • amphibians • fish  • humans
• What are the adaptations of respiratory structures and their functions in gaseous exchange?
• What are the breathing mechanisms found in humans and animals?
• How does gaseous exchange between lungs and blood, and between blood and tissues occur?
• How does the transport of respiratory gases from lungs to tissues and from tissues to lungs occur?
• What are the health issues related to the human respiratory system?

Do You KNOW…

Why is the
respiratory
system
important to
humans and
animals?

Respiratory
Systems in
Humans and
Animals8

CHAPTER

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8.1 Types of Respiratory System

8.1.1 Identify respiratory structures in:
  • insects
  • fish
  • amphibians
  • humans
8.1.2 Describe the adaptation of respiratory

structures and their functions for
gaseous exchange in:

• animals
  • humans
8.1.3 Compare and contrast respiratory

structures in humans and animals.

8.2 Mechanisms of Breathing

8.2.1 Compare and contrast breathing
mechanisms in humans and animals.

8.3 Gaseous Exchange in Humans

8.3.1 Communicate about external and
internal respiration:

• gaseous exchange between lungs
   and blood

• transport of respiratory gases from
   lungs to tissues

• gaseous exchange between blood
   and tissues

• transport of respiratory gases from
   tissues to lungs

8.4 Health Issues Related to the Human
Respiratory System

8.4.1 Narrate the effects of Chronic
Obstructive Pulmonary Disease (COPD)
on the human respiratory system:

• asthma
  • chronic bronchitis
  • emphysema

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Types of Respiratory System
Respiratory structures and their
adaptations for gaseous exchange
You have learned about respiratory organs and systems in humans and
animals in Form 3. The respiratory structure is the respiratory surface
that enables gaseous exchange to occur between respiring organism
cells and their outer environment. You have also learned in Theme 1,
that unicellular organisms such as Amoeba sp. do not need a special
respiratory structure because it has a large total surface area to volume
ratio for gaseous  exchange through diffusion.
The ratio of total surface area to volume (TSA/V) depends on the size of
the organism. The bigger the size of the organism, the smaller the ratio
of total surface area to volume. This means that for large and complex
organisms, the volume of the body that requires oxygen will increase
more than its total surface area. This explains why large and complex
organisms cannot maintain gaseous exchange by diffusion through body
surface only. Large organisms require a special respiratory structure for
the efficient exchange of gases.
How are the respiratory structures of large-sized organisms adapted for
efficient exchange of gases?

8.1

8.1.2

• Large ratio of total surface area to volume (TSA/V) for the
efficient exchange of respiratory gases.

• A thin respiratory structure that is one cell thick, allows the diffusion
of respiratory gases to occur.

• The surface of the respiratory structure is always moist for
respiratory gases to dissolve in them.

• The respiratory structure is complete with a network of blood
capillaries (except for insects), that allows for the efficient delivery of
respiratory gases.

Adaptations of respiratory structures for efficient exchange of
gases in big organisms

Study the effects of
an increase
in total surface area
on diffusion as an
analogy in gaseous
exchange.

Activity Zone

Activity: To study the
respiratory structure in
insects, frogs and rats

ICT 8.1

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The fish respiratory structure and its
adaptations
The respiratory structure of fish is the gills (Figure 8.2). The gills are made
up of a line of filament that is supported by the gill arch. The following
characteristics of filament enable the rapid exchange of respiratory gases.

• The filament has many thin and flat projections called lamella
(plural: lamellae). A large number of filaments and lamellae gives a
large total surface area for an efficient gaseous exchange process.

• The lamella membrane is thin and supplied with many blood
capillaries for easy absorption and transport of oxygen and carbon
dioxide.

The insect respiratory structure and its adaptations
The breathing system of insects is the tracheal system (Figure 8.1).
• There are small pores in the thorax and abdomen of insects called spiracles. The spiracle allows

the intake of air into the air tube system, which is the tracheal system.
• The trachea branches out to form finer tubes called the tracheole. Tracheole is the respiratory

surface. The tracheole has the following characteristics that allow for efficient respiratory
gaseous exchange.
– A large number of tracheoles provides a large total surface area for the exchange of gases.
– The tracheole wall is thin and moist. This allows oxygen gas to diffuse into the cells while

carbon dioxide quickly diffuses out of the cells into the tracheole.
• Some insects have air sacs in their trachea system. This sac is filled with air to speed up the

delivery of respiratory gas during active body movements.

FIGURE 8.1 The tracheal system in a grasshopper

air sacs

trachea

oxygen

spiracle

body cells
carbon
dioxide

trachea
tracheole

spiracles

8.1.28.1.1

Why can’t fish gills
function if the fish is
not in the water?

Brainstorm!

PHOTOGRAPH 8.1 Fish gills

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• The surface of the lungs is folded to increase the total surface area
for the exchange of gases (Figure 8.3).

• The thin lung membrane eases the diffusion of respiratory gases.

• The moist lung walls enable respiratory gases to dissolve in them.

• The lungs are also rich with a network of blood capillaries to
transport respiratory gases.

FIGURE 8.3 The respiratory structure
of frogs

The frog respiratory structure and its adaptations

8.1.28.1.1

lungs
skin

FIGURE 8.2 Respiratory structure of a fish

gill arch gill filaments

lamella

gills

In an inactive state, the frog uses its skin for gaseous
exchange (Figure 8.3).

• The skin is thin and highly permeable to respiratory
gases.

• The moist skin allows respiratory gases to dissolve in
it.

• Beneath the skin, there are many networks of blood
capillaries to transport respiratory gases.

Skin

Lungs

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The human respiratory structure and its
adaptations
The human respiratory structure is the alveolus which has the
characteristics for efficient respiratory gaseous exchange
(Figure 8.4):
• A large number of alveoli provides a large total surface area

for the diffusion of respiratory gases.
• The alveolus wall is always moist. Oxygen and carbon dioxide

can dissolve easily, and diffuse through the walls into the
blood capillaries.

• The alveolus is surrounded by a large network of blood
capillaries to hasten the diffusion of respiratory gases.

• The thin alveolus wall, that is as thick as one cell, makes the
diffusion of gases much easier.

Comparison and contrast of respiratory
structures in humans and animals
Table 8.1 shows the similarities and differences between the respiratory
structures of humans and animals.

TABLE 8.1 Similarities and differences between the respiratory structures of humans and animals

8.1.38.1.28.1.1

FIGURE 8.4 Alveolus

gill arch gill filaments

lamella

gills

bronchiole

alveolus

blood capillaries

• All respiratory structures have a large ratio of total surface area to volume for an efficient exchange
of respiratory gases.

• All respiratory structures are thin and this makes the diffusion of respiratory gases much faster.

• All respiratory structures are moist and this allows respiratory gases to dissolve in them.

• The respiratory structure is complete with a network of blood capillaries (except insects), that allows
for efficient transport of respiratory gases.

Similarities

Differences

Characteristics Insects Fish Frogs Humans

Respiratory structure Tracheole
Filament and
lamella

Skin and lungs Alveolus

How the large ratio of
total surface area to
volume for the respiratory
structure is achieved

Large
number of
tracheoles

Large number
of filaments
and lamellae

• The surface in the
lungs is folded

• Overall skin surface

Large
number of
alveoli

1 State the adaptations of the human
respiratory structure.

2 Explain how the frog skin is adapted
for efficient exchange of gases.

3 State the characteristics of tracheoles
that help with gaseous exchange in
insects.

4 Predict what will happen to a fish if its
gills are torn after being caught in a
net.

8.1Formative Practice

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When inhaling air, the
abdominal muscles will relax.
This will reduce the air pressure
in the trachea and air enters
into the trachea through the
spiracle.

Video: Breathing mechanism
of insects

(Accessed on 21 August 2019)

Mechanisms of Breathing
Humans and animals have different breathing mechanisms. Breathing
refers to the repetitive inhalation and exhalation process.8.2

The abdominal muscles will
contract when air is exhaled. This
will increase the air pressure in the
trachea and subsequently forces air
out of the spiracle.

Breathing mechanism of insects
Abdominal muscles that relax and contract enables air to
go in and out of the trachea.

Breathing mechanism of frogs
Frogs breathe through the mouth and lungs while in an active state. The
sequence of inhalation and exhalation is summarised below.

mouth closes glottis closes

the floor of the
buccopharyngeal
cavity is lowered

nostrils close

the floor of the
buccopharyngeal
cavity is raised

nostrils open
glottis opens glottis opens

• When the frog breathes
through the nostrils, the
mouth and glottis are
closed and the floor of the
buccopharyngeal cavity is
lowered.

• The low air pressure in the
mouth cavity draws air
into the buccopharyngeal
cavity through the nostrils.

• When the glottis opens,
the nostrils close
and the floor of the
buccopharyngeal cavity is
raised.

• The increased air pressure
pushes air into the lungs.

• When the lungs contract, air
is expelled from the lungs.

• This is helped by the
abdominal pressure and the
elasticity of the lungs.

• Some air is expelled through
the nostrils while the rest
is mixed with the air in the
buccopharyngeal cavity.

Inhalation Exhalation

Buccopharyngeal
cavity is filled with air

Exhalation Air is forced into the
lungs

8.2.1

carbon dioxide
ICT 8.2

air enters

spiracles
oxygen

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8.2.1

• When the mouth opens, the floor of the
buccal cavity is lowered.

• At the same time, the opercular cavity is
enlarged and the operculum opening
is closed.

• This reduces the pressure in the buccal
cavity.

• Water from the outside which contains
dissolved oxygen enters the mouth.

• When the mouth is closed, the floor of the
buccal cavity is raised.

• Water enters through the gill lamella and
gaseous exchange between blood and
water occurs through diffusion.

• At the same time, the operculum muscle
relaxes and the opercular cavity becomes
smaller.

• The volume of the buccal cavity is reduced
and the pressure in the buccal cavity
becomes higher than the pressure outside.

• The high pressure causes water to flow
through the operculum opening.

INHALATION EXHALATION

Breathing mechanism of fish
The breathing mechanism of fish is aided by its
mouth movement and operculum. Ventilation takes
place when the fish swims by opening and closing
its operculum. This pushes water into the mouth and
subsequently through the gills. The ventilation increases the
flow of water in the respiratory surface.

Dorsal view

mouth opens mouth closes

floor of the buccal
cavity is lowered floor of the buccal

cavity is raised

gill arch

the operculum
opening is
closed

the
operculum
opening is
openedwater flows

out

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8.2.1

Breathing mechanism of humans
The inhalation and exhalation mechanisms of humans are shown in Figure 8.5.

INHALATION

EXHALATION

1

1

3
2

4
5

2

4
3

5
FIGURE 8.5 The inhalation and exhalation mechanisms of humans

AR The external intercostal muscles relax
while the internal intercostal muscles
contract.

The external intercostal muscles
contract while the internal intercostal
muscles relax.

At the same time, the diaphragm
muscles contract and the diaphragm
moves downwards to become flat and
horizontal.

This action causes the ribcage to move
upwards and outwards.

Both mechanisms cause the volume
of the thorax cavity to increase and the
pressure of the thorax cavity decreases.

The higher atmospheric pressure from
outside forces air into the lungs.

This action causes the ribcage to move
downwards and inwards.

Both movements cause the volume of
the thoracic cavity to reduce and the
pressure of the thorax cavity to increase.

At the same time, the diaphragm
muscles relax and the diaphragm
curves upwards to form a dome.

Air is pushed out of the lungs.

ribs

intercostal
muscle

diaphragm

vertebral
column

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TABLE 8.2 Comparison between breathing mechanisms in humans and animals

8.2.1

Construct a model
to show the actions
of diaphragm
muscles during
breathing in
humans.

Activity Zone

Compare and contrast breathing mechanisms in
humans and animals
What are the similarities and the differences between breathing mechanisms in humans
and animals? Table 8.2 explains the comparison between the breathing mechanisms in
humans and animals.

• Humans and animals have special muscular structures to expand and contract the
respiratory cavity.

• The breathing mechanism involves changes in the volume and pressure in the
respiratory cavity.

Similarities

Differences between breathing mechanisms of insects, fish, frogs and humans

Characteristics Insects Fish Frogs Humans

Respiratory
aperture

Spiracle
Mouth and
operculum

Nostrils Nostrils

Structure that
helps breathing

Thorax,
abdomen

Operculum and
muscular floor
of buccal cavity

Muscular
buccopharyngeal
wall

Diaphragm,
ribcage and
intercostal
muscles

Breathing
mechanism

Assisted
by the
contraction
and
relaxation of
abdominal
muscles

Assisted by
movements of
the floor of the
buccal cavity
and operculum

Assisted by
the rapid
movement of the
buccopharyngeal
cavity floor and
elasticity of the
lungs

Assisted by the
contraction and
relaxation of
the intercostal
muscles and
the diaphragm
muscles as well
as the movement
of the rib cage
upward and
outward, and
downward and
inward

1 State the function of the spiracle
in the breathing mechanism of
insects.

2 How do abdominal muscles help
insects to breathe?

3 State the two differences
between the respiratory
mechanisms of fish
and humans.

4 Explain the mechanism of
inhalation in humans.

8.2Formative Practice

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Gaseous Exchange in Humans
Partial pressure of oxygen and carbon
dioxide
Gas diffusion depends on the partial pressure difference between two
areas. The gas diffuses from an area where its partial pressure is higher
to an area where its partial pressure is lower, which is down a partial
pressure gradient.

8.3

8.3.1

FIGURE 8.6 Gaseous exchange and
the transport of respiratory gases in
blood circulation

In the lungs, blood that enters the lung capillaries contains a higher partial pressure
of carbon dioxide compared to the alveolus. Carbon dioxide diffuses out

from the lung capillaries and into the alveolus before it is expelled into the
atmosphere through the nose and mouth.
The partial pressure of oxygen in the alveolus is higher than the lung
capillaries. Oxygen diffuses into the lung capillaries. Oxygen combines with
haemoglobin in erythrocytes to form oxyhaemoglobin.

Cellular respiration releases carbon dioxide. The partial pressure of carbon dioxide in
cells is higher than tissue capillaries.

Carbon dioxide diffuses out from the body cells into the tissue capillaries and is
transported back to the lungs.

When blood reaches the tissue through the tissue capillaries, the partial
pressure of oxygen in the blood is higher than that of body cells because cellular
respiration uses oxygen.

Oxyhaemoglobin breaks down and oxygen diffuses from the tissue capillaries
to the body cells.

Gaseous exchange and the transport of respiratory gases

oxygen

alveolus

Blood that leaves the lungs
through the pulmonary vein has a
high partial pressure of oxygen
and a low partial pressure of
carbon dioxide.

oxygen

body cells

carbon
dioxide

arteriol

lung
capillary

carbon dioxide

Blood that enters the lungs
through the pulmonary artery
has a low partial pressure
of oxygen and a high partial
pressure of carbon dioxide.

pulmonary
artery

pulmonary
vein

alveolus

lung
capillaries

erythrocytes

tissue capillary

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Explain why the
haemoglobin in
foetus has a higher
percentage of oxygen
saturation compared to
haemoglobin in adults.

Brainstorm!

8.3.1

Explain why exposure
to carbon monoxide
for a very short period
is more dangerous
for an individual as
compared to exposure
to carbon dioxide.

Brainstorm!

1 What is the value of the partial
pressure of oxygen in the
atmospheric pressure?

2 In what form is carbon dioxide
transported in human blood
circulatory system?

3 Explain how carbon dioxide
is transported from the lung
capillaries to the alveolus.

4 In what form is oxygen carried
to the tissues?

8.3Formative Practice

Atmospheric pressure
at sea level is
760 mm Hg. As the
atmosphere consists
of 21% oxygen (as per
volume), the partial
pressure of oxygen is
0.21 x 760 mm Hg or
160 mm Hg. This means
that the oxygen pressure
in the atmospheric
pressure is 160 mm Hg.
The partial pressure of
carbon dioxide at sea
level is 0.23 mm Hg.

Biological Lens

Transport of carbon dioxide in the blood
circulatory system
Carbon dioxide is transported in three ways:
• 70% is carried in the form of bicarbonate ion (HCO3

—)
• 23% carbon dioxide combines with haemoglobin to form

carbaminohaemoglobin
• 7% is dissolved and carried as carbonic acid (H2CO3)

• Carbon dioxide (CO2) released by the body cells binds with
water (H2O) in the erythrocyte to form carbonic acid (H2CO3).

• The carbonic anhydrase enzyme in erythrocyte catalyses
this reaction.

• Carbonic acid (H2CO3) will break down into bicarbonate ion
(HCO3

– ) and hydrogen ion (H+).

• Then HCO3
– diffuses into the blood plasma and is carried to

the lungs.

• When the bicarbonate ion in blood plasma reaches the lung
capillaries, it diffuses back into the erythrocyte.

• The bicarbonate ion combines again with a hydrogen ion (H+ ) to
form carbonic acid (H2CO3).

• Carbonic acid ( H2CO3) then breaks down into carbon dioxide
and water.

• Carbon dioxide diffuses through the lung capillaries into the
alveolus and is expelled during exhalation.

The transport of carbon dioxide from body cells to tissue
capillaries

The transport of carbon dioxide from lung capillaries to the
alveolus

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Health Issues Related to the
Human Respiratory System
Chronic Obstructive Pulmonary Disease (COPD) comprises asthma,
chronic bronchitis and emphysema. In emphysema, the alveolus loses
its elasticity and increases in size. The alveolus wall is damaged, the total
surface area of alveolus decreases and the gaseous exchange becomes less
efficient.
In chronic bronchitis, the bronchiole becomes inflamed, swollen and
blocked. This reduces the flow of air and causes difficulties in breathing.
A large amount of mucus formed will cause continuous coughing.
Damaged cilium causes difficulty in expelling mucus.
For an asthmatic patient, the bronchiole walls become swollen and thick.
The opening of the bronchiole tube becomes smaller and the air passage
becomes narrower. This condition leads to difficulties in breathing and
causes breathlessness. Figure 8.7 shows the lungs of a COPD patient.

8.4

normal air
passage

bronchiole walls of
the patient become
swollen and thick

air passage
narrows

Normal
 bronchiole

Bronchiole of
 an asthma patient

Bronchiole of a
chronic bronchitis
patient

bronchiole
becomes
narrow

alveolus
walls are
damaged

inflamed bronchioles
in patients generate
excessive mucus

Normal
 bronchiole

Normal alveolus  Alveolus of an
emphysema
patient

8.4.1

FIGURE 8.7 COPD disease

Discuss the causal
factors and methods
of treatment for
asthma, chronic
bronchitis and
emphysema.

Activity Zone

1 What are the effects of chronic bronchitis on
the bronchiole?

2 Explain the condition of bronchiole walls in
asthmatic patients.

3 How does the usage of an inhaler help an
asthmatic patient to breathe?

4 Explain why the gaseous exchange becomes
less efficient for an emphysema patient.

8.4Formative Practice

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Have you mastered the following important concepts?
• The respiratory structure in animals and humans
• Respiratory structure adaptations and its function in the exchange of gases
• Respiratory structure of humans and animals
• Breathing mechanisms in humans and animals
• Gaseous exchange between lungs and blood and between blood and tissues
• Gaseous exchange from lungs to tissues and from tissues to lungs
• Health issues related to human respiration

Health Issues
Related to the

Human Respiratory
System

RESPIRATORY SYSTEMS IN HUMANS AND ANIMALS

• Insects: tracheal
system and
tracheole

• Fish: gill
• Amphibian: lungs

and moist skin
• Human: trachea,

bronchus and
alveolus

• Oxygen is transported
in the form of
oxyhaemoglobin

• Carbon dioxide is
transported in the form
of bicarbonate ion,
carbaminohaemoglobin
and carbonic acid

Chronic Obstructive
Pulmonary Disease
(COPD): asthma,
chronic bronchitis
and emphysema

Breathing is
the process of
inhalation and
exhalation

Subject to the
partial pressure
of carbon
dioxide and
oxygen

Types of
Respiratory

System

Mechanisms of
Breathing

Gaseous
Exchange in

Humans

Summary

Self Reflection

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1 Explain why a transportation system is not required to transport  respiratory gases in
 insects.

2 Why are the lungs of amphibians not as efficient as human lungs?

3 The diaphragm of an individual no longer functions normally due to an accident. Explain
 how this condition affects the breathing mechanism of the individual.

4 How does an increase in heartbeat rate during an emergency, help a person to face the
 emergency?

5 (a)  A hardcore smoker can easily suffer from a prolonged cough. Explain how this
  condition affects the function of the respiratory system.

(b) Describe another illness that may be easily contracted by a hardcore smoker.
   (c) Explain the effects of tar that is present in cigarette smoke on the smoker.

6 One of the effects of emphysema is the loss of elasticity in the alveolus. Explain the effect
of this on gaseous exchange.

7 (a) Name structures P and Q that help humans and fish, respectively in gaseous
exchange.

FIGURE 1

(b) Explain the breathing mechanism of fish.
  (C) Describe two similarities of structure P and Q that has been adapted to help P and

Q function effectively.
  (d) Give two reasons why the rate of oxygen supply to human cells is faster than the

rate of oxygen supply to fish cells if both are of the same size.

Essay Questions

8 The human respiratory systems of humans and grasshoppers have different adaptations
 to maximise the  rate of gaseous exchange. State the similarities and differences
 between the human respiratory system and the grasshopper breathing system.

P

Q

Summative Practice 8

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9  (a) Explain how air is inhaled into the lungs.
  (b) Explain how a carbon dioxide molecule is carried from the body cell to the alveolus to

be expelled.

Enrichment

10 Air pollution makes breathing difficult in animals and humans. If you are a scientist, which
animal will you choose as an indicator of pollution level in a particular area? Explain the
justification of your choice.

11 All mammals breathe through the lungs, as with mammals that live in the sea such as
whales. How does the whale breathe in water?

Complete answers are
available by scanning the
QR code provided

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3D food
printer

• What are the structural components of the human digestive system?
• How is food digested and absorbed?
• How does food assimilation occur?
• How does defaecation occur?
• What is a balanced diet?

Do You Know...

Can food be
designed to meet
the nutritional
needs of humans?

Nutrition and the
Human Digestive
System9

CHAPTER

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9.1 Digestive System

9.1.1 Identify structures of the
human digestive system.

9.2 Digestion

9.2.1 Describe the types of
digestion:

• physical digestion
  • chemical digestion
9.2.2 Analyse the process

and products of
carbohydrate digestion
in the mouth.

9.2.3 Analyse the process
and products of protein
digestion in the stomach.

9.2.4 Describe digestions of
carbohydrates, proteins
and lipids in the small
intestine.

9.2.5 Conduct experiments
to study digestions of
starch, proteins and
lipids in food samples.

9.3 Absorption

9.3.1 Identify the structure of a
villus in the ileum.

9.3.2 Communicate about the
adaptations of ileum and
villus in the absorption of
digested food.

9.4 Assimilation

9.4.1 Describe the roles of the
circulatory system in the
assimilation of digested
food.

9.4.2 Discuss the functions of
liver in the assimilation of
digested food:

• metabolism of
 digested food
 (carbohydrates and
 proteins)

• storage of nutrients
  • detoxification

9.5 Defaecation

9.5.1 Explain the functions of
the large intestine:

• absorption of water
 and vitamins

• formation of faeces

9.6 Balanced Diet

9.6.1 Conduct an experiment
to study the energy
values in food samples.

9.6.2 Conduct an experiment
to determine the
contents of vitamin C in
fruit or vegetable juices.

9.6.3 Justify the modification
of diets for individuals
who:

• experience obesity
  • experience a specific

disease
   – diabetes mellitus

– cardiovascular
   – cancer

9.7 Health Issues Related to
Digestive System and Eating
Habits

9.7.1 Predict the effects of
modifying digestive
organs on human health.

9.7.2 Outline health issues
related to defaecation.

9.7.3 Correlate health issues
that are related to eating
habits.

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Digestive System
Structure of the human digestive system
The human digestive system is made up of a long and muscular alimentary
canal that starts from the mouth to the anus (Figure 9.1).
The parts of the alimentary canal include the mouth, oesophagus, stomach,
small intestine, large intestine and anus. The other organs in the digestive
system are liver, gallbladder and pancreas. Salivary, gastric and intestinal
glands secrete digestive juices into the alimentary canal.

9.1
Digestion
Types of digestion
Digestion is the process that breaks down large and complex pieces of food
into smaller and simple pieces that can be dissolved for easy absorption.
Digestion is made up of two parts, that is, physical digestion and chemical
digestion.

9.2
Physical digestion Chemical digestion

The mechanical
breakdown of
food to form small
particles

The decomposition
process of complex
molecules into
simple molecules

Involves chewing
and peristalsis

Involves enzymes
reaction

AR

FIGURE 9.1 Human digestive system

9.2.29.2.19.1.1

Digestion of
carbohydrates in the
mouth
The digestive process begins in the mouth.
The presence of food in the mouth stimulates
the secretion of saliva from the salivary
glands.

stomach

oesophagus

rectum

anus

small intestine

large intestine

tongue

bile duct

gallbladder

salivary gland mouth

pharynx

pancreas

liver

appendix

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• Saliva contains salivary amylase that hydrolyses starch to maltose.
• The pH of the saliva ranges between 6.5–7.5, which  is suitable for salivary amylase to act at its

optimum.

Starch + water                        maltose
Salivary amylase

FIGURE 9.2 Peristalsis

the muscular
walls of the
oesophagus

contract

the muscular
walls of the
oesophagus

relax
bolus

oesophagus

Digestion of protein in the

FIGURE 9.3  Structure of stomach and gastric
     gland tissues

Pepsinogen is an inactive enzyme that is activated
by hydrochloric acid to become pepsin. Pepsin then
hydrolyses proteins into polypeptides.

Protein + water                      polypeptides
pepsin

9.2.3

oesophagus

duodenum

epithelium

stomach

sphincter

gastric gland

Saliva helps food to form bolus and makes it easier
to be swallowed. When swallowing, the epiglottis
will close the trachea opening to prevent food from
entering the trachea. In the oesophagus, the food
bolus is moved by peristalsis.
Peristalsis is the rhythmic contraction and relaxation
of muscles along the alimentary canal. Peristalsis
pushes the bolus through the oesophagus until it
enters the stomach (Figure 9.2).

Chew slowly a
small piece of
bread. Observe
the taste when
you first started
chewing and after
a few minutes of
chewing. Is there
any difference in the
taste of the bread?

Brainstorm!

esofagus

mukosa

submukosa

perut

epitelium

sfinkter
pilorus

duodenum

mucous
cells
parietal
cells

chief
cells

stomach
The surface of the stomach wall is lined with epithelial
cells that have undergone adaptations in structure
and  function to form gastric glands (Figure 9.3).
These epithelial cells are chief cells, parietal cells
and mucous cells.
• Chief cells secrete pepsinogen.
• Parietal cells secrete hydrochloric acid.
• Mucous cells secrete mucus.

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The functions of hydrochloric acid are to:
(a) prepare a medium with a suitable pH (pH

1.5–2.0) for pepsin to act
(b) stop the enzymatic action of salivary

amylase
(c) kill bacteria in food
The function of mucus is to protect the stomach
wall from the reaction of hydrochloric acid and
digestive enzymes.

The food in the stomach is mixed with gastric
juice made up of hydrochloric acid and pepsin.
Food is churned by the peristaltic action of
the stomach wall muscles for a few hours.
The contents in the stomach finally change to
a semifluid called chyme. Chyme enters the
duodenum slowly when the sphincter muscle
relaxes.

FIGURE 9.4 Components that are involved
in digestion that take place in the small
intestine

9.2.4

Digestions of carbohydrates, proteins and lipids in the
small intestine
The small intestine consists of duodenum, jejunum and ileum. Duodenum is the first part of the
small intestine which receives chyme from the stomach. Duodenum also receives bile produced by
the liver and pancreatic juice secreted by the pancreas (Figure 9.4).

LIVER

• Produces bile

• The gallbladder stores bile.

• The bile flows into the
duodenum through the bile
duct.

• Functions of bile

– neutralise the acidic
chyme

– prepare an alkali
condition (pH 7.6–8.6)
for enzyme action in the
duodenum

– emulsify lipids by
breaking down lipids into
tiny droplets to increase
surface area for lipase
activity.

PANCREAS

The pancreas secretes
pancreatic amylase, trypsin
and lipase into the duodenum
through the pancreatic duct.

DUODENUM

• Pancreatic amylase hydrolyses starch to maltose

Starch + water  maltose

• Trypsin hydrolyses polypeptides into shorter peptides.

Polypeptide + water  peptides

• Lipase hydrolyses lipids into fatty acids and glycerols.

Lipid + water  fatty acid and glycerol

pancreatic amylase

trypsin

lipase

duodenum

stomach

chyme

liver

gallbladder

bile duct

pancreas

pancreatic duct

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Glands on the ileum wall secrete mucus and intestinal juice  that contains
maltase, sucrase, lactase, lipase and erepsin. The alkali medium in the
ileum allows enzymes to act at its optimum.

Chemical digestion
involves enzyme-
catalysed hydrolysis
reaction. For example,
an enzyme is needed
in the decomposition
of starch into glucose.

Across the fields

9.2.5

CARBOHYDRATE DIGESTION

• Maltase hydrolyses maltose into
glucose.

Maltose + water  glucose

• Sucrase hydrolyses sucrose into
glucose and fructose.

Sucrose + water

• Lactase hydrolyses lactose into
glucose and galactose.

Lactose + water

maltase

sucrase

lactase glucose +
galactose

glucose +
fructose

ICT 9.1

Video: Processes of digestion,
absorption and defaecation

(Accessed on 21 August 2019)

Activities2.1 Experiment
Studying the digestion of starch in a
food sample

Activity 9.1

Problem statement
What is the effect of amylase on starch?

Hypothesis
Amylase hydrolyses starch to a reducing sugar.

Variables
Manipulated: Presence of amylase
Responding: Presence of reducing sugar
Fixed: Temperature of water bath at 37˚C,
concentration of starch suspension and volume of mixture

Materials
0.5% amylase solution, 1% starch suspension, iodine solution, Benedict’s solution and distilled water

Apparatus
Tripod stand, Bunsen burner, wire gauze, 500 ml beaker, test tube holder, thermometer, stopwatch,
test tube, dropper, glass rod and measuring cylinder

LIPID DIGESTION

Lipase hydrolyses lipids
into fatty acids and
glycerols.

lipase Fatty acids
+ glycerol

Lipid
+ water

Erepsin hydrolyses
peptides into amino acids.

PROTEIN DIGESTION

erepsin amino
acids

Peptides
+ water

water bath
(37 °C)

thermometer

A BA B

water bath
(37 °C)

thermometer

A B

3 ml of 1% starch
suspension + 3 ml
of distilled water

3 ml of 1% starch
suspension + 3 ml
of 0.5% amylase
solution

water bath
(37 °C)

thermometer

A B

3 ml of 1% starch
suspension + 3 ml
of distilled water

3 ml of 1% starch
suspension + 3 ml
of 0.5% amylase
solution

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9.2.5

Procedure
 1 Label 2 test tubes as A and B.

2 Add 3 ml of 1% starch suspension to each test tube.

3 Fill test tube A with 3 ml of 0.5% amylase solution and test tube B with 3 ml of distilled water.

4 Soak both test tubes in a water bath with a temperature of 37 °C for 10 minutes.

5 After 10 minutes, remove 2 ml of the solution from test tube A and put it into a different test
tube.  Add 3 drops of Benedict’s solution to that test tube and heat the test tube in a boiling
water bath for 1 minute. Record the colour of the content.

6 Add 2 drops of iodine solution to the remainder of test tube A. Observe and record the colour
of the contents.

7 Repeat steps 5 and 6 for test tube B.

Results

Test tube Contents Iodine test Benedict’s test

A 1% starch suspension + 0.5% amylase
solution

B 1% starch suspension + distilled water

Discussion
 1 Explain the reaction that occurs in test tube A.

2 What is the purpose of preparing test tube B?

Conclusion
Is the hypothesis accepted? Suggest a suitable conclusion for this experiment.

Problem statement
What is the effect of pepsin on protein?

Hypothesis
Pepsin hydrolyses proteins in the albumen suspension into polypeptides.

Variables
Manipulated: Presence of pepsin
Responding: Clarity or turbidity of mixture after 20 minutes.
Fixed: Temperature at 37˚C, concentration of pepsin solution and dilute hydrochloric acid

Materials
Albumen suspension (egg white), 1% pepsin solution, distilled water and 0.1 M dilute hydrochloric
acid

Apparatus
Test tube, measuring cylinder, 500 ml beaker, water bath at 37 °C, dropper, thermometer and
stopwatch.

Experiment
Studying digestion of protein in a food
sample

Activity 9.2

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9.2.5

Experiment
Studying the digestion of lipids in a food
sample

Activity 9.3

Procedure
 1 Prepare an apparatus set-up as follows.

2 Soak all test tubes in a water bath at 37 °C.

3 Observe the condition of mixtures in test tubes A and B at the beginning
of the experiment and after 20 minutes.

Results

Test tube
Clarity or turbidity

0 minute 20 minute

A

B

Discussion
 1 Explain the results achieved in test tube A and B.

2 What is the purpose of adding hydrochloric  acid into each test tube?

Conclusion
Is the hypothesis accepted? Suggest a suitable conclusion for this experiment.

Problem statement
What is the effect of lipase on lipid?

Hypothesis
Lipase hydrolyses lipids into fatty acids and glycerols.

Variables
Manipulated: Presence of lipase
Responding: Time taken for the phenolphthalein indicator to turn from pink to colourless
Fixed: Temperature at 37°C, volume of cooking oil and combined volume

Materials
Cooking oil, 0.2 M sodium carbonate solution, dishwashing liquid, phenolphthalein indicator, distilled
water and lipase

Test tube A: 5 ml of albumen suspension + 1 ml of 0.1 M hydrochloric
acid + 1 ml 1% pepsin solution

Test tube B: 5 ml of albumen suspension + 1 ml of 0.1 M hydrochloric
acid + 1 ml distilled water

water bath
(37 °C)

thermometer

A BA B

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1 Explain the importance of the digestion
process for humans.

2 Name the structures in the alimentary canal
that are involved in food digestion.

3 Name the main cells in the gastric glands
and explain the functions of these cells.

4 The small intestine secretes a few types of
enzymes to complete the digestion process.
Explain how these enzymes complete the
digestion process.

9.1Formative Practice

Apparatus
Two test tubes, test tube rack, water bath at 37 °C, 5 ml and 1 ml syringes, dropper, stopper and
stopwatch

Procedure
 1 Prepare two test tubes and label them as A and B.

2 Fill each test tube A and B with the following:

• 2 ml of cooking oil
• 1 ml of 0.2 M sodium carbonate solution
• 1 ml of dishwashing liquid

3 Close both test tubes with stoppers. Shake both test tubes
vigorously after adding the dishwashing liquid.

4 Add 3 drops of phenolphthalein indicator to each test tube and
shake the test tube.

5 Add 1 ml of lipase into test tube A and 1 ml of distilled water into test tube B.

6 Soak both test tubes in a water bath at 37°C.

7 Record the time taken for the phenolphthalein indicator to turn from pink to colourless.

Results

Discussion
 1 Why is a phenolphthalein indicator used in this experiment?

2 What is the purpose of adding dishwashing liquid into each test tube?

3 Explain the reaction that happens in test tube A.

4 Explain the results obtained in test tube B.

Conclusion
Is the hypothesis accepted? State the suitable conclusion for this experiment.

Test tube Contents
Time taken for the phenolphthalein indicator to turn

from pink to colourless (minute)

A 1 ml of lipase

B 1 ml of distilled water

9.2.5

water bath
(37 °C)

thermometer

A BA B

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9.3.1 9.3.2

Absorption
The adaptations of ileum and villus in the
absorption of digested food
Simple molecules produced from the digested food are absorbed in the ileum
of the small intestine.

9.3

VILLUS (PLURAL: VILLI)

ILEUM

MICROVILLUS

Villus has the following
adaptations to absorb nutrients
(Figure 9.5):

• The epithelial layer of the
villus is one cell thick. This helps
accelerate nutrient absorption.

• Goblet cells secrete mucus to aid
digestion.

• The network of blood capillaries helps
to transport digestive products to the
whole body.

• Lacteal carries droplets of fatty acids and
glycerol.

• The intestinal glands secrete intestinal
juices that have digestive enzymes.

The long ileum is adapted
to absorb nutrients
because its internal layer
is folded and covered by
tiny projections called
villi (singular: villus) (Figure 9.5).

On the surface of the villus
epithelium, there are many
tiny projections called
microvillus. Microvillus
provides a large surface
area  to increase the rate of
nutrient absorption (Figure 9.5). FIGURE 9.5 Adaptations of ileum and villi

to absorb digested food.

ileum

cross section of a small
 intestine

lacteal

villus

epithelial cells

blood capillaries

lymph vessel

nucleus

mucus

goblet
cells

microvillus
basement
membrane

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Lakteal

Kapilari darah

Petunjuk:

Glukosa

Asid amino

Asid lemak

Giserol

Titisan halus lipid

Galaktosa

Fruktosa

9.3.2

FIGURE 9.6 Absorption of digested food

Absorption of digested food is summarised in Figure 9.6 and Table 9.1.

ICT 9.2

Video: View inside the
small intestine

(Accessed on 21
August 2019)

1  Name the main structures for the absorption
of digested food.

2 Name the structure in the villus involved in
the transporting of the following nutrients:

(a) amino acids

(b) vitamins A and E

3 Explain the adaptations of the small intestine
to increase the surface area for absorption of
nutrients.

4 Explain how the following substances can be
transported across the plasma membrane.

(a) Glucose, galactose and amino acids
(b) Fatty acids and glycerol

9.2Formative Practice

TABLE 9.1 Method of food absorption in the ileum

Digested food
Absorbed
through

Methods of
absorption

Fructose

Epithelial cells
into blood
capillaries

Facilitated diffusion

Glucose and galactose Active transport

Amino acids Active transport

Vitamins B and C Absorbed with water

Water Osmosis

Fatty acids and glycerols
recombine through the
condensation process to
form tiny droplets of lipids
in the epithelial cells

Epithelial cells
into lacteal

Simple diffusion

Vitamins A, D, E, K
dissolve in the lipid

Simple diffusion

Millennial Career

A gastroenterologist
is a medical specialist
who specialises in
the human digestive
system.

Millennial Career

Gather information
about the
absorption of
alcohol and drugs.

Activity Zone

lacteal

blood capillaries

Indicator:

Glucose

Amino acids

Fatty acids

Glycerol

Lipid droplets

Galactose

Fructose

lacteal

blood capillaries

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Assimilation
The role of the circulatory system
The human circulatory system consists of the blood circulation system
and the lymphatic system to help transport nutrients to be assimilated.
In the assimilation process that occurs in cells, nutrients are used to form
complex compounds or structures of components. The blood capillaries
in the small intestine combine to form the hepatic portal vein that
transports blood to the liver.
Lacteals combine to form bigger lymph vessels in the lymphatic system.
Then, the contents of the lymph vessels enter the thoracic duct that
flows into the left subclavian vein. This lipid is then transported by
blood throughout the body.

Functions of liver in the assimilation of
digested food
The liver is the regulator that controls the quantity of nutrients that
enter the blood circulatory system. The liver carries out the following
functions.

9.4

9.4.1 9.4.2

METABOLISM OF DIGESTED FOOD

STORAGE OF NUTRIENTS

DETOXIFICATION

• Glucose is used for cellular respiration. Amino acids are used for
synthesising plasma proteins and enzymes.

• Through the deamination process, excess amino acids are turned
into urea to be excreted through the urine.

Excess glucose is converted to glycogen to be stored.

• Liver cells expel toxic substances from the blood.

• Toxic substances are expelled through the urine.

Liver cirrhosis
is a type of liver
disease caused
by factors such as
alcoholic drinks,
toxic substances
and hepatitis. Liver
cells are replaced
by scarred cells
that can cause
failure in the liver
functions. Hepatitis
is an inflammation
of the liver caused
by viral infection,
toxic substances
or autoimmune
reaction
(Photograph 9.1).

Biological Lens

Conduct a research
on the various
functions of the
liver and produce a
scrap book

Activity Zone

Normal liver Liver of a cirrhosis
patient

PHOTOGRAPH 9.1 Normal
liver and liver of a cirrhosis
patient

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9.4.2

1 State the meaning of assimilation.

2 Explain the functions of the liver in the assimilation of digested food.

9.3Formative Practice

AMINO ACIDS

• Amino acids are used
to synthesise new
protoplasm and also
repair damaged
tissues.

• Amino acids are used to
synthesise hormones
and enzymes.

GLUCOSE

• Glucose is oxidised through
cellular respiration to release
energy, water and carbon
dioxide.

• Excess glucose is kept as
glycogen in muscles.

• Energy is used for cell
processes such as protein
synthesis.

LIPIDS

• Lipids such as  phospholipid
and cholesterol are the primary
components that build the plasma
membrane.

• Excess fats are kept in adipose
tissues found underneath the skin
as stored energy.

• Fat is oxidised to release energy
when there is insufficient glucose.

AMINO ACIDS GLUCOSE

• The liver synthesises plasma protein and
enzymes from amino acids.

• Excess amino acids cannot be stored in
the body and are broken down through the
deamination process to form urea which is
then expelled.

• When the glucose supply is insufficient, the
liver converts amino acids into glucose.

• Glucose in the liver is used for cellular respiration
when required by the body and the excess is
converted to glycogen and stored in the liver.

• When the glucose level in the blood decreases and
the body needs energy, glycogen is converted to
glucose.

• When the glycogen supply reaches a maximum
level, the excess glucose is converted to fats.

FIGURE 9.7 Transportation of nutrients and
the assimilation in the liver and cells

ASSIMILATION PROCESS IN THE LIVER

ASSIMILATION PROCESS IN CELLS

li

carbohydrates protein lipid

small
intestines

fatty acids + glycerol

glucose

glucose

amino acid

amino
acids

lipid

urea
excess

excess

hepatic
portal vein

excreted by
the kidneys

cellular respiration

glycogen
is stored

I understand the difference between pitch and volume.

liver

synthesis of
protoplasm
(in the cell)

synthesis of
plasma proteins
and enzymes

plasma
membrane
synthesis

body cell

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9.5.1

9.5
The large intestine
has a huge population
of bacteria. There
are more than 1000
different species of
bacteria in the large
intestine and a healthy
balance between
beneficial and less
beneficial bacteria
is very important for
health and a stable
environment in the
alimentary canal.

Biological Lens

What is the effect
of antibiotics
on the large
intestine’s bacterial
population?

Brainstorm!

1   State the main function of the
large intestine.

2   What are the substances
absorbed in the large
intestine?

3 Explain the importance
of water absorption and
vitamins in the large intestine.

4 Explain the formation process
of faeces.

9.4Formative Practice

FORMATION OF FAECES

ABSORPTION OF WATER AND VITAMINS

• After the water is absorbed, the remaining waste is a semisolid called faeces. Faeces
contains dead cells from the inner layer of the intestine, waste products such as bile
pigments, bacteria and toxic substances.

• The walls of the large intestine secrete mucus to smoothen the movement of faeces until the
anus. The movement of faeces takes about 12 to 24 hours before entering the rectum.

• The faeces will accumulate in the rectum until the pressure in the rectum increases and
triggers the need to expel faeces from the body.

• The rectum muscles will contract to expel faeces from the anus. This process is called
defaecation.

Substances absorbed are

• water and mineral salts

• metabolic byproducts of some bacteria such
as vitamin B, vitamin K and folic acid. FIGURE 9.8 Large intestines

colon

caecum
appendix anus

rectum

Defaecation
Functions of the large
intestine
After the absorption of nutrients is
completed in the ileum, undigested food,
dead cells, epithelial cells, fibre and water
enter the large intestine and move slowly
through peristaltic action. Fibre consists
of cellulose walls of plant cells. The large
intestine carries out two main functions:
• absorption of water

and vitamins
• formation of faeces

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2.1 Activities ExperimentStudying the energy value of food samplesActivity 9.4

Balanced Diet
Energy value in a food sample
A balanced diet refers to a diet that consists of all seven food classes
(carbohydrates, lipids, proteins, vitamins, mineral salts, fibre and water)
in the correct proportion and balanced quantity according to individual
needs so that optimal health can be maintained.

9.6

4.2 J g-1 °C-1 refers
to the specific heat
capacity of water,
that is, the energy
required to increase
the temperature of 1 g
of water by 1 °C.

Across the fields

Problem statement
Which food sample has the highest energy value?

Hypothesis
Groundnuts have a higher energy value compared to
cashew nuts.

Variables
Manipulated: Types of food samples
Responding: Energy value of food sample
Fixed: Water mass

Materials
Distilled water, food samples (cashew nuts and groundnuts),
cotton wool and plasticine

Apparatus
Retort stand with a clamp, thermometer, boiling tube,
long needle, electronic weighing scale, barrier, measuring
cylinder and Bunsen burner

1 kilojoule = 1000 joule

Biological Lens

1 calorie (cal) = 4.2 joule (J)

9.6.1

ENERGY VALUE

• Energy value is the total amount of energy released when one
gram of food is oxidised completely.

• The energy value in food is measured in the form of heat energy,
that is, in kilojoule per gram (kJ g-1).

• Another unit of heat energy is calorie.

• 1 calorie or 4.2 joule is defined as the quantity of heat energy
needed to raise the temperature of 1 gram water by
1 degree Celsius (°C) at a pressure of 1 standard atmosphere.

•  Energy value of food (kJ g-1)

= Water mass (g) × 4.2 J g-1 °C-1 × Increase in water temperature (°C)
Mass of food sample (g) × 1000

barrier

thermometer

boiling tube

distilled
water

food sample

needle

plasticine

retort
stand

cotton
wool

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9.6.2

Procedure
 1 Weigh a cashew nut using an electronic weighing scale and record its mass.

2 Measure 20 ml of distilled water using a measuring cylinder and pour it into a boiling tube.

3 Clamp the boiling tube to the retort stand and put in the thermometer.

4 Fix the position of the thermometer using cotton wool.

5 Record the initial temperature of the distilled water.

6 Stick the cashew nut on the needle and hold the needle upright using plasticine.

7 Place the barrier around the apparatus set-up.

8 Light the cashew nut using a Bunsen burner and place it below the boiling tube.

9 Stir the water in the boiling tube slowly and record its highest temperature after the cashew nut
has completely burned.

10 Replace the water in the boiling tube.

11 Repeat steps 1 to 9 using groundnuts.

12 Calculate the energy value for each food sample using the following formula:

= Water mass (g) × 4.2 J g-1 °C–1 × Increase in water temperature (°C)
Food sample mass (g) × 1000

Energy value of
food (kJ g–1)

13 Record your results in the table below.

Results

Food
sample

Food
sample
mass (g)

Initial
temperature

of water
(°C)

Final
temperature
of water (°C)

Increase of
Temperature

(°C)

Energy value
of food
(kJ g–1)

Cashew nuts

Groundnuts

Discussion
 1 Which food sample shows the highest energy value?

2 State two precautionary steps for this experiment.

3 Compare the energy value of food samples obtained from this experiment with their theoretical
energy values. Are there any differences? If yes, explain why.

Conclusion
Is the hypothesis accepted? Suggest a suitable conclusion for this experiment.

The contents of vitamin C in fruit or vegetables juices
The nutrient content in various types of food is different. For example, the vitamin C
content in fruits and vegetables are different.

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9.6.2

Activities 2.1 Experiment
Determining the contents of vitamin C in fruit juice
and vegetable juice.

Problem statement
Which fruit juice or vegetable juice has the highest content of vitamin C?

Hypothesis
Orange juice has the highest content of vitamin C compared to lime juice and carrot juice.

Variables
Manipulated: Types of fruit and vegetable juices
Response: Volume of fruit juice or vegetable juice needed to decolourise DCPIP solution
Fixed: Concentration of DCPIP solution and concentration of an ascorbic acid solution

Materials
Orange juice, lime juice and fresh carrot juice, 0.1% ascorbic acid solution, 1% DCPIP solution and
distilled water

Apparatus
Syringe needles (1 ml and 5 ml), knife, 50 ml beaker, specimen tube, juicer and sieve

Procedure
 1 Put 1 ml of 1% DCPIP solution in a specimen tube.

2   Fill the 5 ml syringe needle with a 0.1% ascorbic acid solution.
Ensure that there are no air bubbles trapped in it.

3 Insert the tip of the syringe needle into the specimen tube and drip
ascorbic acid drop by drop into the DCPIP solution while stirring
slowly until the blue colour of the DCPIP solution is decolourised.

4 Record the volume of the 0.1% ascorbic acid solution needed to
decolourise the  blue colour of the DCPIP solution.

5 Repeat steps 1 to 4 twice to get the average volume for each
different juice.

6 Record the volume of each juice in the table below.

7 Calculate the concentration of vitamin C of each juice using the following formula.

Percentage of vitamin C =
volume of ascorbic acid solution

volume of juice used × 0.1%

Vitamin C concentration (mg ml-1) = volume of ascorbic acid solution
volume of juice used

× 1.0%

Results

Solution / Juice
Volume of solution/juice

required to decolourise DCPIP
solution (ml)

Vitamin C
concentration

(%)

Vitamin C concentration
(mg ml-1)

1 2 3 Average
0.1% ascorbic
acid solution

0.1

Orange juice
Lime juice
Carrot juice

specimen tube

ascorbic acid

DCPIP solution

Activity 9.5

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One of the factors that affect the loss of vitamin C content is temperature.  Therefore, fruit or
vegetables must be kept at a suitable temperature range to preserve vitamin C.

9.6.2

Discussion
 1 Which juice has the highest content of vitamin C?

2 Why is a 0.1% ascorbic acid solution used as the standard?

Conclusion
Is the hypothesis accepted? Suggest a suitable conclusion for this experiment.

Activities2.1 Experiment
Studying the effect of temperature on vitamin C in
orange juice

Activity 9.6

Problem statement
What is the most suitable ambient temperature to keep orange juice?

Hypothesis
Orange juice stored at a low ambient temperature has the highest content of vitamin C.

Variables
Manipulated: Ambient temperature
Responding: Volume of orange juice required to decolourise DCPIP solution
Fixed: Volume of DCPIP solution

Materials
Oranges, 1% DCPIP solution and ice

Apparatus
Specimen tube, knife, syringe needles (1 ml and 5 ml), beakers (50 ml and 100 ml),
Bunsen burner, tripod stand, sieve and wire gauze

Procedure
 1 Prepare 60 ml of orange juice.

2  Label the beakers A, B and C. Pour 20 ml of orange juice into each beaker.

3 Soak beaker A in ice, leave beaker B at room temperature and soak beaker C in boiling water
for 30 minutes.

4 After 30 minutes, determine the vitamin C content in the orange juice as shown in Activity 9.5.

5 Calculate the concentration of vitamin C in the orange juice at each different temperature.

Results
Record your results in an appropriate table.

Ensure that
the juice is not
exposed too long
to avoid oxidation.

Take Note!

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The cause of obesity
Obesity is caused by the storage of excess fats as a result of
imbalanced food intake and use of energy.

Effects of obesity
Individuals who are obese need to reduce the intake of carbohydrates
and fats as well as increase the intake of vegetables and fruits.
Otherwise, a diet with excessive saturated fats and high cholesterol
may cause diabetes mellitus and various cardiovascular diseases such
as atherosclerosis and hypertension which may result in heart attacks
(myocardial infarction) or stroke if not treated.

Diet modifications for specific individuals

9.6.3

Discussion
 1 Is there a difference in the vitamin C content for the juice at different temperatures?

2 What is the effect of temperature on vitamin C in the orange juice?

3 Based on the results, suggest the best way to ensure that you get a high content of vitamin C
from fruit juice or vegetable juice.

Conclusion
Is the hypothesis accepted? Suggest a suitable conclusion for this experiment.

A balanced diet for each individual will vary according to lifestyle,
health conditions and specific nutritional requirements.   Each
individual must make wise choices based on a nutrition guide.
For example, suggestions for nutritional needs can be made based
on Pinggan Sihat Malaysia. Pinggan Sihat Malaysia illustrates
the relative quantity of various food classes in a balanced diet
(Photograph 9.2).
Excessive food intake that is rich in saturated fats can cause health
problems such as obesity and cardiovascular diseases.

Cancer patients who are undergoing cancer treatment, need to modify
their diet to ensure they receive sufficient energy, reduce the risk of
infections and enable quick recovery.

Millennial Career

Nutritionists are
specialists in the
field of nutrition
who advise
specific individuals
on suitable diets.

Millennial Career

Plan meals based
on Pinggan Sihat
Malaysia for different
individuals such as
obese individuals,
cancer patients and
heart patients.

Activity Zone

PHOTOGRAPH 9.2
A sample serving based on
Pinggan Sihat Malaysia

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duodenum

jejunum

jejunum

gastric
sac

Part of the
stomach
that has
been
bypassed

Part of the
duodenum
that has been
bypassed

Health Issues Related to the
Digestive System and Eating
Habits

Adaptation of digestive organs
Obesity is a health issue on the rise throughout the world. Although
obesity can be controlled through diet management and routine
exercise programmes, at times, obesity requires medical treatment.
Specialist doctors may suggest surgical procedures to reduce body
weight such as gastric bypass (Figure 9.9). A gastric bypass involves a
reduction of the stomach size using various methods of surgery.
Among the short-term side effects of this surgery are acid reflux,
nausea, vomiting, expanded oesophagus, certain food prohibitions
and risk of infection. The long-term side effects are dizziness, low
blood sugar level, malnutrition, stomach ulcer and defaecation
problems.

9.7

FIGURE 9.9 Gastric bypass

food

digestive juice

9.7.1 9.7.2

Health issues related to defaecation
The food class that is most important in the defaecation process
is fibre. Intake of diet that is high in fibre such as fruits and
vegetables can smoothen bowel movements.  This can prevent
health problems such as constipation, colon cancer, rectum cancer
and haemorrhoid.
Some of the functions of fibre are to:
• stimulate peristalsis
• absorb and expel toxic substances
• regulate the absorption of glucose especially for diabetes

mellitus patients
• increase the population of beneficial bacteria in the large

intestine
Besides, the intake of a large amount of water can ensure that the
faeces stay soft and move easily along the large intestine to aid the
process of defaecation.

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Health issues related to eating habits
Apart from a balanced diet, eating habits also play an important role in fulfilling our energy
requirements and maintaining our health. Poor eating habits and an imbalanced diet can
cause numerous health problems such as gastritis, muscle dysmorphia, anorexia nervosa and
bulimia nervosa.

9.7.3

ANOREXIA
 NERVOSA

MUSCLE
 DYSMORPHIA BULIMIA NERVOSA

GASTRITIS

Gastritis refers to the
inflammation and corrosion of
the stomach epithelial layer
by gastric juice when there
is no food in the stomach.
Untreated gastritis can result
in gastric ulcers. The causes

of gastritis include eating
irregular quantities of food at

irregular hours and excessive
intake of alcohol or painkillers.

Anorexia
nervosa is
quite common
amongst
teenage
girls who are
obsessed with
their body weight.
Anorexics will avoid
food to achieve their
ideal body weight. They also
suffer from psychological problems
and nutrient deficiency because of their
normal digestive system is affected.

Some individuals
feel that their size
is small with not
enough growth.
So, they subject
themselves
to extreme
weightlifting
training and exercise.
Sometimes, they consume
steroids or muscle building
supplements. This health issue is called
muscle dysmorphia.

For people with bulimia
nervosa who are also
obsessed with controlling
their body weight, they
will eat a lot and vomit out

the food that they have
eaten or take laxatives that

cause diarrhoea. In the long
run, the patient may suffer from

dehydration, nutritional problems and
eventually cardiovascular disease or kidney failure.

1 In your opinion, why is fibre
important in the defaecation
process. Explain your
answer.

2 Predict the effect of
modifying digestive organs
such as gastric bypass on
human health.

9.5Formative Practice
Do a case study about
the following health issues
related eating habits:
•  diabetes type 2
•  obesity
•  acid reflux
•  pica

Activity Zone

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NUTRITION AND THE HUMAN DIGESTIVE SYSTEM

• Digestion
• Absorption
• Assimilation
• Defaecation

• Energy value
• Contents of vitamin C in

fruit or vegetables juices
• Diet modifications for

specific individuals

• The effects of modifying
digestive organs on human
health

• Health issues related to
defaecation

• Health issues related to eating
habits

Health Issues Related to the
Digestive System and Eating

Habits
Digestive System Balanced Diet

Have you mastered the following important concepts?
• Structure of the human digestive system
• Mechanism of digestion
• Process and products of carbohydrate digestion in the mouth
• Process and products of protein digestion in the stomach
• Digestions of carbohydrates, proteins and lipids in the small intestine
• Adaptations of ileum and villus in the absorption of digested food
• Assimilation of digested food and liver functions
• Defaecation
• Balanced diet and energy value in food samples
• Diet modifications for specific individuals
• Health issues related to the digestive system and eating habits

Summary

Self Reflection

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1 Some people cannot drink milk because it causes diarrhoea and a bloated stomach. Explain
why.

2 Amin had some meat dishes for lunch. Explain how the protein is digested in Amin’s
stomach.

3 An individual has the following eating habits:

Explain how this eating habit can affect the health of this individual.

4 Figure 1 shows the alimentary canal in humans.

FIGURE 1

(a) Name structures X and Y.

(b) (i) The enzymes in X are only effective in an alkaline environment. Explain how an
    alkaline environment is maintained in X.

(ii) Explain how Y is involved in the digestion of carbohydrates in X.

(c) Name the enzyme found in Z. Explain how this enzyme functions in the digestion of
proteins.

(d) A student enjoys eating a lot of oranges.  Explain the effect of eating too many oranges
on the digestion of starch in X.

Summative Practice 9

Overeating in a short period of time followed by intentional throwing
up on purpose after each meal.

X

Z

Y

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Essay Questions

5 Explain the processes that fat molecules undergo starting from the duodenum until it is
finally used by body cells.

6 A teenager had the following for his breakfast.

Explain what happens to the final digested products of his breakfast in his body cells.

7 (a)   Explain why a diet rich in fats is not good for health.

(b) Suggest suitable types of food for someone who wants to reduce weight and reduce
the risk of contracting cardiovascular disease. Explain your answer.

(c) Explain the processes of starch digestion, absorption and assimilation in the human
body.

Enrichment

8 Medicines in the form of capsules are not broken down in the stomach but absorbed easily
by the small intestine. When the blood sample of the patient is taken and analysed, it is
found that the molecular structure of this medicine is different from its original molecular
structure. Explain why.

9 How are drinks with added artificial sweeteners produced and marketed?

10 Nowadays, many individuals prefer ready-to-eat or frozen food products due to their busy
lifestyles. Predict the health risks that may arise if these foods are taken continuously for a
long period of time and in large quantities.

Buttered bread – 2 pieces
Hard-boiled eggs – 2

Fresh milk – 1 glass
Apple – 1

Complete answers are
available by scanning the
QR code provided

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• What are the components of the blood circulatory system?
• How does the heart pump blood?• How does the lymphatic system return tissue fluids into the blood circulatory system?

• What are the health issues related to the human circulatory and lymphatic systems?

Do you KNOW...

What is a
mechanical heart?

CHAPTER

10 Transport in
Humans and
Animals

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10.1  Types of Circulatory System

10.1.1 Justify the necessity of transport
systems in complex multicellular
organisms.

10.1.2 Identify substances that are
transported by the transport
system: • substances required by
a cell • waste products of a cell

10.1.3 Conceptualise types of circulatory
system in complex multicellular
organisms.
• open circulatory system
• closed circulatory system

10.1.4 Compare and contrast circulatory
systems in complex multicellular
organisms: • insects
• fish • amphibians • humans

10.2  Circulatory System of Humans

10.2.1 Describe components of the
human circulatory system:

• heart • blood vessel • blood
 10.2.2 Explain the composition of blood:

• blood plasma • blood cells
 10.2.3 Compare and contrast the types of

blood vessels:
• artery • vein • capillary

10.2.4 Label the structure of a human
heart and associated blood
vessels: • aorta • vena cava
• pulmonary artery and pulmonary
vein
• coronary artery and coronary
vein.
• semilunar valve
• bicuspid valve and tricuspid
valve • septum

10.2.5 Describe the functions of parts of
the heart.

10.3  Mechanism of Heartbeat

10.3.1 Describe the human heartbeat
mechanism:
• sinoatrial node (pacemaker)
• atrioventricular node
• bundle of His • Purkinje fibres

10.3.2 Communicate about forces that
cause the blood to circulate in
humans: • pumping of the heart
• contraction of skeletal muscles

10.4  Mechanism of Blood Clotting

10.4.1 Justify the necessity for blood
clotting mechanism.

10.4.2 Describe blood clotting
mechanism.

10.4.3 Describe health issues related to
blood clotting: • thrombosis
• embolism • haemophilia

10.5  Blood Groups of Humans

10.5.1 Describe ABO blood group.
 10.5.2 Correlate ABO blood group with

blood donation.
 10.5.3 Describe the Rhesus factor.
 10.5.4 Reason out the incompatibility of

Rhesus factor in pregnancies.

10.6  Health Issues Related to the Human
  Circulatory System

10.6.1 Justify the necessity for a healthy
circulatory system.

10.6.2 Communicate about
cardiovascular diseases.

10.7  Lymphatic System of Humans

10.7.1 Synthesise the process of
formation of tissue fluid and lymph.

10.7.2 Compare and contrast the
contents of lymph and:

• tissue fluid • blood
 10.7.3 Describe components of the

lymphatic system: • lymph
• lymphatic capillaries

• lymphatic vessels• lymph nodes
• lymphatic organs

10.7.4 Justify the necessity of the
lymphatic system:

• complements the blood
   circulatory system

• transports lipid-soluble
   substances
• body defence

10.8  Health Issues Related to the Human
  Lymphatic System

10.8.1 Describe health issues related to
the lymphatic system.

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body cells

The necessity for transport systems in
complex multicellular organisms
Each living cell requires essential substances such as oxygen and
nutrients, and expels cellular waste products such as carbon dioxide
and nitrogenous wastes.

In Chapter 2, you learned how unicellular organisms such as Amoeba sp.
get their essentials and expel wastes by diffusion from and to its external
surroundings. Unicellular organisms have a small body mass. Therefore,
the total surface area to volume ratio (TSA/V) of the organism is large.
As such, Amoeba sp. does not require a specialised transport system to
transport substances in and out of the cell.

What about multicellular organisms? Can multicellular organisms
obtain all essential substances and expel wastes by simple diffusion like
unicellular organisms?

Large complex multicellular organisms cannot obtain essential
substances and expel wastes by diffusion because their TSA/V is small.
The distance between the external environment and the cell is too far for
direct substance exchange. So, how do complex multicellular organisms
get essential substances for their cells?

Types of Circulatory System 10.1

10.1.210.1.1

FIGURE 10.2 Substance
exchange for multicellular
organisms

external environment
is far away from cells

external environment

epidermis

Substance
exchange can occur
by diffusion because
the cells are in the
environment.

Substance
exchange cannot
occur by diffusion
because the
cells are too far
away from the
environment.

FIGURE 10.1 Substance
exchange for unicellular
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ICT 10.1

Activity: Studying the effects of
changes in total surface area
to volume ratio (TSA/V) on the

diffusion rate.

• In an open circulatory system,
haemolymph flows directly into the
body cavity (haemocoel) and bathes the
cells.

• Haemolymph is a blood-like nutritious
liquid found in most invertebrates such
as insects and molluscs.

• In a closed circulatory system, blood is
always contained in a continuous closed
blood vessel and is distributed to the
whole body.

• The exchange of substances that are
essential to cells such as oxygen and
nutrients occurs across the walls of
blood capillaries.

Types of circulatory systems in multicellular
organisms
The circulatory system in multicellular organisms is divided into two
types: open circulatory system and closed circulatory system.

To address this problem, multicellular organisms have an internal
transportation system. In vertebrates, the transportation system is
called the blood circulatory system.

Before studying further the blood circulatory system, conduct an
experiment to study the effects of changes in TSA/V on the diffusion
rate.

OPEN CIRCULATORY SYSTEM CLOSED CIRCULATORY SYSTEM

10.1.3

haemolymph vessel

heart

haemocoel

cells

open-ended vessel

ttt

blood vessel

cells

heart
blood blood capillary

haemolymph

haemolymph vessel

heart

haemocoel

cells

open-ended vessel

ttt

blood vessel

cells

heart
blood blood capillary

haemolymph

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FIGURE 10.5 The blood circulatory system of fish

anterior

aorta

ostium

posterior

FIGURE 10.3 Dorsal view of
insect heart

FIGURE 10.4 The open
circulatory system in insects

aorta

anterior

aorta

ostium

posterior

aorta heart

ostium
haemocoel

• The circulatory system of insects is
an open circulatory system. This
means that one or more hearts pump
haemolymph through the blood vessels
into the haemocoel.

• Haemolymph flows out from the heart
into the haemocoel when the heart
contracts.

• In the haemocoel, substance exchange
between haemolymph and body cells
occurs through diffusion.

• When the heart relaxes, haemolymph
flows back into the heart through tiny
openings called ostium.

Circulatory System of Insects

mixed blood

mixed blood

vein

atrium

artery

heart

gill capillaries

systemic capillaries

ventricle

oxygenated blood
Indicator:

deoxygenated blood

mixed blood

CIRCULATORY SYSTEM

10.1.4

• The heart of the fish has two chambers,
that is, an atrium (plural: atria) and a
ventricle.

• Blood that leaves the ventricle is pumped
to the gill capillaries to enable gaseous
exchange.

• The gill capillaries carry blood to the
blood vessels that transport oxygenated
blood to systemic capillaries.

• In the systemic capillaries, oxygen
diffuses into the tissues while carbon
dioxide diffuses from the tissue into the
capillaries.

• The deoxygenated blood is then returned
to the heart atrium through the veins.

• As the blood flows in one direction, the
fish circulatory system is known as a
single circulatory system.

Circulatory System of Fish

OPEN CIRCULATORY SYSTEM

heart

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10.1.4

Indicator:
oxygenated blood

mixed blood
deoxygenated blood

CLOSED CIRCULATORY SYSTEM

1 Deoxygenated
blood from body is
transported to the
right atrium.

2 Oxygenated blood
from lungs and skin
is transported by
the pulmonary vein
to the left atrium.

4 The ventricle
then pumps the
blood through the
pulmocutaneous (lungs
and skin) and systemic
circulations.

3 Blood from both
atria enters one
ventricle. Although
there is some mixing
of oxygenated and
deoxygenated blood
in the ventricle, most
of the oxygenated
blood remains on
the left side of the
ventricle while the
deoxygenated blood
remains on the right
side of the ventricle.

FIGURE 10.6 The blood
circulatory system of amphibians FIGURE 10.7 The blood circulatory system of humans

Pulmonary circulation
• Deoxygenated blood is transported

through the pulmonary artery to the
lungs for gaseous exchange.

• Oxygenated blood from the lungs is
returned to the left atrium and flows
into the left ventricle.

Systemic circulation
• Blood is pumped from the heart to all

the body tissues through the aorta.
• Then the deoxygenated blood returns

to the right atrium through vena cava.

• The heart of an amphibian has three chambers,
that is, two atria and a ventricle. Unlike the single
circulatory system of fish, blood flows in two
directions: pulmocutaneous circulation and
systemic circulation. Therefore, this system is
known as a double circulatory system.

• Amphibians are said to have an incomplete double
circulatory system because the deoxygenated
blood and the oxygenated blood are mixed.

• Pulmocutaneous circulation transports blood to
the lungs and skin, and the exchange of gases
takes place here. Systemic circulation transports
oxygenated blood to the body tissues and returns
the deoxygenated blood to the right atrium through
the veins.

Circulatory System of Amphibians

lung capillaries and skin

pulmocutaneous
circulation

right
atrium

left
atrium

ventricle
systemic circulation

systemic capillaries

pulmonary
vein

vena cava

pulmonary artery

aorta

systemic capillaries

lung capillaries

left
atrium

left
ventricleright

ventricle

right
atrium

• The human heart consists of four
chambers: two atria and two ventricles
that are separated completely.

• Humans have a double circulatory
system. This means that in one
complete circulatory cycle, blood
flows in the blood vessels through the
heart twice. As there are two different
circulations, humans are said to have
a complete double circulatory
system  because the deoxygenated
blood and the oxygenated blood do
not mix.

Circulatory System of Humans

4

21

3

oxygenated
blood
deoxygenated
blood

Indicator:

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10.1.4

TABLE 10.1 Similarities and differences between circulatory systems in complex multicellular organisms
Similarities

The circulatory system is found in all multicellular organisms.

The circulatory system consists of a heart to pump blood or haemolymph (in insects).

The circulatory system functions to transport nutrients and wastes.

The heart has valves that ensure blood flows in one direction.

Differences

Organism Insects Fish Amphibians Humans

Types of
circulatory
system

Open blood
circulatory system

Closed blood
circulatory system

Closed blood
circulatory system

Closed blood
circulatory system

Number of
circulations

–

Single (blood
flows in the blood
vessel and through
the heart once
in a complete
circulation)

Double
(blood flows in
the blood vessel
and through the
heart twice in
one complete
circulation)

Double
(blood flows in
the blood vessel
and through the
heart twice in
one complete
circulation)

Number of
heart cavities

The heart is made
up of many cavity
segments

Two (one atrium
and one ventricle)

Three (two atria
and one ventricle)

Four (two atria and
two ventricles)

Separation of
oxygenated
blood and
deoxygenated
blood

– –

Incomplete (some
oxygenated blood
is mixed with the
deoxygenated
blood in the
ventricle)

Complete
(oxygenated blood
does not mix with
deoxygenated
blood in the
ventricle)

1 State two differences between the circulatory
systems of fish and humans.

2 Explain why the blood circulatory system of
amphibians is considered as a closed and
incomplete blood circulatory system.

3 The flatworm is a multicellular organism.
However, the flatworm does not require a
specialised transportation system to move
substances in and out of the cell. Explain
why.

4 Explain why insects need one separate
system (the tracheal system) to transport
oxygen.

Formative Practice 10.1

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There are three main components in the circulatory system of humans.
• Blood: A type of connective tissue that is made up of blood plasma,

blood cells and platelets. Blood acts as a medium of transportation.
• Heart: Functions as a muscular pump that circulates blood to the

whole body.
• Blood vessels: Consist of arteries, capillaries and veins that

are connected to the heart, and transport blood to all
the body tissues.

Structure of the heart
Do you know that your heart is as big as your fist? The
heart is located between the lungs in  the thorax cavity
and contains four chambers, namely the left atrium,
right atrium, left ventricle and right ventricle. The left
chamber is separated from the right chamber by a muscular
wall  called septum.

Atrium receives blood that returns to the heart
while the ventricle pumps blood out of the
heart. The ventricle has thicker walls and
contract stronger than the atrium.

The muscular wall of the left ventricle
is much thicker than the muscular wall
of the right ventricle. This is because
the left ventricle has to generate greater
pressure to pump blood out of the
aorta to the whole body while the right
ventricle only has to pump blood to the
lungs.

Circulatory System of
Humans 10.2

A group of researchers
in Malaysia have
produced a device
called MyThrob that
can be used as a
smart examination
and monitoring tool
for heart diseases.
The device studies the
original algorithm that
can detect abnormal
heartbeat and is
suitable to be used for
monitoring at home.

Malaysian Innovation

10.2.1 10.2.4 10.2.5

coronary arteries

coronary veins

Coronary arteries
transport oxygenated
blood for heart tissues
while coronary veins
transport deoxygenated
blood.

arteri koronari

vena koronari
TABLE 10.8 The circulatory system of humans

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aorta

pulmonary artery

pulmonary veins

left atrium

bicuspid valve
coronary vein

septum
left ventricle

vena cava

right ventricle

coronary artery

tricuspid valve

semilunar valves

right atrium

FIGURE 10.9 Longitudinal section of a human heart

10.2.510.2.4

aorta

arteri pulmonari

vena pulmonari

atrium kiri

injap bikuspid

septum

vena kava

ventrikel kanan

injap trikuspid

arteri coronari

atrium kanan

injap sabit

The tricuspid valve
(located between the
right atrium and the right
ventricle) ensures that
blood which flows into the
right ventricle does not
flow back into the right
atrium. This valve consists
of three leaflets.

The pulmonary  artery transports
deoxygenated blood from the heart
to the lungs while the  pulmonary
veins transports oxygenated blood
from the lungs to the heart.

The semilunar
valves at the base of
the pulmonary artery
and the base of the
aorta ensures that
blood which flows
out of the heart does
not flow back into the
ventricle when the
ventricle relaxes.

Aorta is the main blood artery that transports
oxygenated blood to the whole body while the vena
cava is the main vein that transports deoxygenated
blood back to the heart.

The septum separates the left part of the heart
from the right part of the heart and ensures that
the oxygenated blood does not mix with the
deoxygenated blood.

The bicuspid
valve (located
between the
left atrium
and the left
ventricle)
ensures that
blood which
flows into the
left ventricle
does not flow
back into the
left atrium. This
valve consists
of two leaflets.

What would happen
to an individual
if the bicuspid
valve does not
close completely
when the ventricle
relaxes?

Brainstorm!

Video: Animation of
the heart valves

(Accessed on
21 August 2019)

ICT 10.2

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Composition of human blood
The human blood consists of 55% plasma and 45% cell components.
Plasma is the medium of transportation in the body. The components
of blood cells consist of red blood cells or erythrocytes, platelets and
white blood cells or  leucocytes  (Photographs 10.1 and 10.2).

Perfluorocarbon (PFC)
emulsions can be
potentially used as
artificial blood. Studies
have shown that PFC
has the capacity like
blood to transport
oxygen and carbon
dioxide.

Biological Lens

TABLE 10.2 Blood plasma components and the main function of each component
Component Main function

Water Blood plasma consists of 90% water. Water is a medium of
transportation and a solvent for respiratory gas, ions, digestive products
and excretory substances.

Plasma proteins • Fibrinogen plays a role in blood clotting.
• Albumin controls blood osmotic pressure.
• Globulin is a type of antibody that is involved in the body’s defence.

Solutes – nutrients such
as glucose, excretory
substances such as
urea and respiratory gas

• Nutrients are important for energy, growth and maintenance of health.
• Excretory substances are toxic substances that need to be disposed

off from the body.
• Oxygen is required in the respiration of cells.

Hormones and enzymes Hormones control physiological activities in the body. Enzymes are
involved in the metabolic processes of cells.

platelet

leucocyte

erythrocyte

PHOTOGRAPH 10.2
Main structural components of
blood

10.2.2

PHOTOGRAPH 10.1 Main components of blood

Plasma (forms 55% of the blood
volume)

Erythrocytes (forms 45%
of the blood volume)

Leucocytes and platelets (less
than 1% of the blood volume)

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Table 10.3 shows the characteristics and functions of each blood cell type.

TABLE 10.3 Characteristics and functions of blood cell types
Blood cell type Characteristics Functions

Erythrocyte
(red blood cell)

• Has an elastic plasma membrane
• The biconcave disc shape

enables a large TSA/V for efficient
gaseous exchange

• It does not have a nucleus at
the mature stage so that more
haemoglobin can be loaded
into it

• It is produced in the bone
marrow of bones such as the
sternum and ribs

• Can live up to 120 days and is
destroyed in the liver or lymph
through the phagocytosis
process.

• Each erythrocyte has a
haemoglobin which is the red
pigment that gives blood its red
colour.

• Haemoglobin contains a heme
group. The heme group consists
of an iron atom which is the
binding site for oxygen.

• Haemoglobin combines with
oxygen to form oxyhaemoglobin
in high oxygen partial pressure
conditions.

• Oxyhaemoglobin releases oxygen
in tissues or cells when the partial
pressure of oxygen is low.

Platelet • Platelets are produced from
fragments or scraps of cell
cytoplasm that originate from the
bone marrows.

• The life span is less than one
week.

• Involved in the blood clotting
process

FIGURE 10.11 Platelet

7.5 m2.0

pandangan sisi

pandangan atas

mside view

top view

FIGURE 10.10
 Erythrocyte structure

10.2.2

The red blood
cell of frogs has
a nucleus and is
larger than the
red blood cell of
humans. What are
the advantages and
disadvantages of
nucleated red blood
cells?

Brainstorm!

Haemoglobin

iron

oxygen

polypeptide

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10.2.2

Neutrophil
• The nucleus is made up of

two to five lobes.
• Ingests bacterial cells and

dead cells or tissues from
wounds by phagocytosis

Lymphocyte
• Contains a large nucleus with very little

cytoplasm
• Produces antibodies to destroy bacteria and

viruses that enter the body
• Can also produce

antitoxins against toxins
that are produced by
bacteria or viruses

Eosinophil
• The nucleus is made up of

two lobes.
• Releases enzymes that

fight inflammation and
allergy reaction

Monocyte
• The biggest leucocyte
• Spherical-shaped nucleus
• Ingests bacteria and dead cells or

tissues by phagocytosis

Basophil
• The number of basophils

is lowest in the blood
• It contains heparin that

prevents blood clotting

Blood cell type Characteristics and functions

• The shape is irregular and is not fixed
• Contains nucleus
• Does not contain haemoglobin
• Produced in the bone marrow
• Life span is less than five days
• Leucocyte can diffuse out of the capillary pore and fight pathogens in

tissue fluids. It is divided into two types: granulocytes (contain granules)
and agranulocytes (no granules).

• Granulocytes include neutrophils, eosinophils and basophils.
Agranulocytes include lymphocytes and monocytes.

Agranulocyte

PHOTOGRAPH 10.3 Photomicrograph of leucocytes

Granulocytes

Leucocyte
(white blood

cell)

L

E

U

C

O

C

Y

T

E

S

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10.2.3

Human blood vessels

FIGURE 10.12 Relationship between artery, blood capillaries and vein

Arteries are blood vessels that transport
blood out of the heart. The function of the
artery is to quickly transport blood at a high
pressure to the tissues.
The blood in the artery is under high
pressure because of the pumping action of
the heart.
The aorta is the main artery that leaves
the heart. The artery expands when blood
is received from the heart. Therefore, the
artery wall is elastic to stop it from breaking
due to the high-pressured blood that flows
through it.
The branches of an artery become small
vessels known as arterioles when they
reach the body tissues. The arteriole
continues to branch out and ends at the
capillaries. The group of capillaries is called
capillary network.

Capillaries are
blood vessels with
thin walls, as thick
as one cell. Blood
capillaries allow the
exchange of gases to
occur between blood
and cells through
diffusion. Nutrients,
excretory substances
and hormones
diffuse through blood
capillaries.

Capillaries rejoin to
form larger blood
vessels called
venules. The venules
combine to form
veins that transport
blood back to the
heart. Vena cava is
the main vein that
carries deoxygenated
blood back to the
heart. The differences
between arteries,
capillaries and veins
are given in Table 10.4.

ARTERY BLOOD
CAPILLARIES

VEIN

endothelial cells

endothelium
endothelium

connective
tissue

venule
arteriole

smooth
muscle smooth muscle

connective
tissue

Blood capillary

Artery Vein

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lumen (middle space)

erythrocyte

connective
tissues

10.2.3

TABLE 10.4  Differences between arteries, capillaries and veins
Characteristics Artery Capillaries Veins

Wall Wall is thick, muscular
and elastic

Wall is as thick as one
cell, not muscular and
not elastic

Wall is thin, less muscular
and less elastic

Lumen Small Very tiny Large

Valve

No valve except for
semilunar valve at
the base of the aorta
and at the base of the
pulmonary artery

No
Contain valves to maintain
one-way flow of blood

Blood pressure High Low Very low

The direction of
blood flow

From the heart
to the entire body

From the artery to the
vein

From the whole body
to the heart

lumen

elastic
fibre

wall

Kapilari VenaArteri

Kapilari VenaArteri

wall (as thick as one cell)

lumen

Kapilari VenaArteri

lumen

wall

1 What is the function of the bicuspid valve?

2 Explain why some individuals feel nauseous
and faint immediately after donating blood?
Why do some blood donors need to take
iron pills?

3 State two differences between the structures
of erythrocyte and leucocyte.

4 Explain why the left ventricle has a thicker
muscular wall than the right ventricle.

Formative Practice 10.2

PHOTOGRAPH 10.4 Scanning electron microscope shows the cross section of an arteriole (4000x magnification)

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FIGURE 10.13 The location of sinoatrial node, atrioventricular node,
bundle of His and Purkinje fibres

Mechanism of Heartbeat
How is blood circulated to the whole body? In every contraction, the
heart acts as a pump that pumps blood to the whole body. How is every 10.3  heartbeat triggered and sustained?

The heart is made up of cardiac muscles (Photograph 10.5) that intersect
and are connected with one another. This arrangement allows electric
impulses to spread rapidly through the heart and at the same time,
stimulates the cardiac muscle cells to contract simultaneously and
uniformly. Cardiac muscles are myogenic. This means that the heart
contracts and relaxes without receiving any impulse signal from the
nervous system. If the cardiac muscles are stored in a warm oxygenated
solution that contains nutrients, these muscles will contract and relax
rhythmically on their own.

Blood circulation in humans
The produced force that enables blood to circulate in humans is
generated by the pumping of the heart and the contraction of the
skeletal muscles.

PHOTOGRAPH 10.5
Cardiac muscle tissue

The “Medtronic
Micra” pacemaker
is the smallest
artificial pacemaker
in the world. The
size is about the
size of a vitamin
pill and is placed in
the heart without
surgery. The artificial
pacemaker sends
small electrical
charges to stimulate
heartbeat.

Our World of Biology

10.3.1

left ventricleright ventricle

atrioventricular node bundle of His

Purkinje fibres

sinoatrial node

right atrium

left atrium

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Pumping of the heart

The contraction of the heart is initiated and
coordinated by the pacemaker. The pacemaker
is a group of specific heart muscle cells that
initiates the rate of heart contraction and is
located at the right atrium wall (Figure 10.14).

Electrical impulses
in the heart can
be detected by
putting electrodes
on the skin. The
electrocardiogram
is a record of the
electrical activity
that triggers every
heartbeat.

Across the fields

FIGURE 10.14 The sequence of heart contraction that causes the pumping of the heart

The sinoatrial node (SA) generates
electrical impulses. 1

Electrical impulses spread rapidly
in both the atria, causing the atria
to contract simultaneously. The
contraction of the atria helps to pump
blood into the ventricles.

2

The electrical impulses reach the
atrioventricular node. The electrical
impulses spread through the bundle of
His, and the Purkinje fibres up to the
apex of the heart.

3

The electrical impulses spread
from the apex of the heart to the
whole ventricle wall. As a result, the
ventricles contract to pump blood out
to the lungs and body.

4

atria

ventricles

atrioventricular node (AV node)

sinoatrial nodes
(SA nodes)

AR

10.3.2

The pacemaker generates electrical impulses
that spread rapidly through both walls of
the atrium and causes the atrium to contract
rhythmically. The main pacemaker is called
sinoatrial node (SA). The sequence of  heart
muscle contraction that causes the pumping is
shown in Figure 10.14.

Purkinje fibres

bundle of His

apex of
the heart

Purkinje fibres

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The first ‘lub’ sound is produced when
the tricuspid valve and the bicuspid valve
close.1

open valve

closed valve

muscles relax

veins

muscle
contraction
contricts vein

The blood flow in the veins is assisted by:

(a) contraction of the smooth muscles found in the venule and
vein walls;

(b) contraction of skeletal muscles around the veins. The
contraction of skeletal muscles presses and constricts the
veins, causing the valve to open and allow blood to flow
towards the heart. The valve is then closed to prevent the
blood from flowing back towards the foot (Figure 10.16).

FIGURE 10.15 The lub-dub sound of the heart

During heart pumping, the lub-dub sound can be heard. Do you know
what causes this lub-dub sound?
The lub-dub sound is the closing sound of the heart valves.

What would happen
to the valve in the
blood vessels of our
legs if we stand or sit
for too long?

Brainstorm!

Contraction of skeletal muscles around the veins

The pumping of the heart helps in the distribution and flow
of blood through the arteries, arterioles and blood capillaries.
However, the force produced by the pumping of the heart is
insufficient for the blood flow to continue through the veins and
return to the heart. Besides, the blood is forced to flow against
the force of gravity. The presence valve in the veins ensures that
the blood flows in one direction to the heart.

The second ‘dub’ sound is
produced when the semilunar
valves close.2

FIGURE 10.16 Contraction
and relaxation of the foot
skeletal muscles

10.3.2

tricuspid valve bicuspid valve

semilunar
valves

1 Name the main heart
pacemaker.

2 What does the term
myogenic mean?

3 Explain why a person who
stands too long may faint.

4 In what circumstances would
fingers turn pale?

Formative Practice 10.3

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The necessity for blood clotting mechanism
What happens when your finger is injured? Blood will flow from the
wound until you apply pressure directly on the wound. The pressure
you apply may appear to restrict bleeding temporarily; however, the
blood flow is actually stopped by the blood clotting process.

Why must the blood clot on the wound? Blood clotting will stop or
minimise the loss of blood on the injured blood vessel. Blood clotting
also prevents microorganisms such as bacteria from entering the
bloodstream through the damaged blood vessel. The blood pressure is
also maintained because excessive blood loss will lower blood pressure
to a dangerous level. How does blood clotting occur?

Mechanism of blood clotting
Blood clotting involves a series of chemical reactions that takes place in
the blood when someone is injured to prevent excessive bleeding.

Mechanism of Blood
Clotting 10.4

Scientists have
developed a
nanomagnetic
particle that
contains thrombin.
This nanoparticle
is injected into
the injured part
to trigger blood
clotting and to stop
bleeding.

STEM Bulletin

Prothrombin (inactive
plasma protein)

The coagulated platelets, damaged cells and clotting factors
in the blood plasma will form an activator (thrombokinase).
Thrombokinase, with the aid of calcium ions and vitamin K, converts
prothrombin to thrombin.

Fibrin is a threadlike protein fibre that
forms a network on the wound surface to
trap erythrocytes and to close the wound to
prevent blood loss.

Fibrin (insoluble)

TABLE 10.17
Mechanism of blood clotting

Thrombin (active plasma
protein that acts as an enzyme).
Thrombin catalyses the conversion
of fibrinogen to fibrin.

Fibrinogen (soluble)

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HAEMOPHILIA

• Haemophilia is an example of an illness that
prevents blood from clotting.

• Haemophilia is a hereditary illness caused by the
lack of certain clotting factors in the blood.

• Excessive bleeding due to small wounds or
bruises can result in death.

When you sit for
too long, the risk of
thrombosis in legs
will increase. Make
sure that you move
your legs once in a
while.

Our World of Biology

10.4.3

Work in groups
to collect and
interpret information
about thrombosis,
embolism and
haemophilia.
Present your
findings to the
class.

Activity Zone

THROMBOSIS

• Formation of a blood clot (thrombus).

• Thrombosis happens as a result of:

– damage in blood vessels, or

– sluggish blood flow that causes clotting factors to
  accumulate

EMBOLISM

• When a blood clot is transported by blood flow, the blood clot is
called embolus.

• If the embolus gets stuck in a tiny blood vessel, the blood flow will
stop.

1 At the end of the blood clotting mechanism,
fibrin will be formed to trap erythrocytes.
Explain the meaning of fibrin and its function.

2 Describe two health issues related to blood
clotting.

3 Explain the mechanism of blood clotting.

4 Explain why the formation of blood clots in
the blood vessel can cause a heart attack.

Formative Practice 10.4

Health issues related to blood
clotting

Under normal conditions, blood does not
clot in blood vessels that are not damaged
because of some anticoagulants such as
heparin. What happens when the blood
clotting mechanism of an individual does
not function?

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ABO blood group
Do you know your blood group? Human blood is classified into A,
B, AB and O groups. Donation and transfusion of blood is based on
the compatibility of the blood group of the donor and the recipient.
This is because the recipient has antibodies in the blood serum that
can act against the antigen on the red blood cells of the donor. Blood
transfusion from a donor to a recipient must take into consideration
the blood group type of the donor and the recipient (Table 10.6). If
the blood group of both the donor and receiver is not compatible,
the red blood cells of the recipient will experience agglutination
(coagulation).

Blood Groups of Humans  10.5

Rhesus Factor
Another antigen found on the surface of the red blood cells is the
Rhesus factor (Rh factor). The red blood cells of an individual
with the Rh factor or antigen D are known as Rh-positive. An
individual who does not possess the Rh factor or antigen D is known
as Rh-negative.

If the blood of a Rh-positive donor mixes with the blood of a Rh-
negative recipient, the blood of the recipient will react by producing
the Rhesus antibody or anti-D antibody. When the recipient receives
another dose of Rh-positive blood, the Rhesus antibody will cause the
agglutination of the donor blood cells. This situation could result in
the death of the recipient.

TABLE 10.5 Antigen and antibody in blood groups
Blood
group

Antigen on red blood cells  Antibody in the blood
serum

A Antigen A Anti-B

B Antigen B Anti-A

AB Antigen A and Antigen B No

O No Anti-A and Anti-B

TABLE 10.6  Compatibility of blood donor group with the recipient
Blood
group

Can donate blood to
blood groups

Can receive blood from
blood groups

A A and AB only A and O only

B B and AB only B and O only

AB AB only A, B, AB and O

O A, B, AB and O O only

10.5.1 10.5.2 10.5.3

Blood group A Blood group B

Blood group AB Blood group O

antigen A

antigen A
no antigens

antigen B

no antibodies

antigen B

anti-B antibody

anti-B antibody

anti-A antibody

anti-A antibody

red blood cell

red blood cell

red blood cell

red blood cellBlood group A Blood group B

Blood group AB Blood group O

antigen A

antigen A
no antigens

antigen B

no antibodies

antigen B

anti-B antibody

anti-B antibody

anti-A antibody

anti-A antibody

red blood cell

red blood cell

red blood cell

red blood cell

Blood group A Blood group B

Blood group AB Blood group O

antigen A

antigen A
no antigens

antigen B

no antibodies

antigen B

anti-B antibody

anti-B antibody

anti-A antibody

anti-A antibody

red blood cell

red blood cell

red blood cell

red blood cellBlood group A Blood group B

Blood group AB Blood group O

antigen A

antigen A
no antigens

antigen B

no antibodies

antigen B

anti-B antibody

anti-B antibody

anti-A antibody

anti-A antibody

red blood cell

red blood cell

red blood cell

red blood cell

FIGURE 10.18 Antigens and
antibodies in different blood
groups

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Usually, problems
will arise when an
Rh-negative mother
marries an
Rh-positive father
and conceives an
Rh-positive foetus.

10.5.4

Pregnancy and the Rhesus factor

Formative Practice 10.5
 1 State the blood group which is the universal

donor.

2 Predict what will happen if the blood
group of both recipient and donor is not
compatible.

3 Three babies P, Q and R have blood groups
B, O and AB respectively. Three pairs of
parents have the following blood groups:

The first pair of parents: B and O

The second pair of parents: A and B

The third pair of parents: AB and O

Match the babies with their correct parents.

4 An Rh-positive male marries an Rh-negative
female. The first Rh-positive child is alive but
the second child who is also Rh-positive did
not survive. Explain why.

As a result, the white
blood cells in the
mother’s blood will react
and produce anti-D
antibodies that will
flow back through the
placenta into the foetal
blood circulatory system.

During the last month of
pregnancy, fragments
of foetal blood cells
containing antigen D
cross the placenta
and enter the blood
circulation of the mother.

However, the
concentration
of antibodies
produced is
not enough
to affect the
first child. But
the anti-D
antibodies
will last in
the blood
circulatory
system of the
mother.

The problem arises when
the second child is also
Rh-positive. The anti-D
antibodies that are present
in the mother’s blood cross
the placenta and destroy
the red blood cells of that
foetus. The symptoms
of this disease are called
erythroblastosis fetalis.
The second foetus dies if
the blood is not replaced
with Rh-negative blood
through blood transfusion.

The antibodies will destroy
the red blood cells of the
Rh-positive baby before
or immediately after birth.

In a less serious situation,
the baby may suffer from
anaemia and mental
retardation. However,
this problem can now be
addressed by treating
the affected mother with
anti-Rhesus globulins after
the first pregnancy to stop
the formation of anti-D
antibodies.

Rh-positive
Rh-negative
Anti-D
antibodies

Indicator:

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The necessity for a healthy circulatory system
A healthy circulatory system is important to ensure optimum health.
How do we ensure that our circulatory system is healthy? Among the
practices for maintaining the circulatory system are a balanced intake of
food that is low in fat and regular exercise. The practice of not smoking
and not drinking alcoholic drinks also ensures a healthy circulatory
system.

Cardiovascular diseases
Do you know that cardiovascular diseases are the leading cause of
death in our country? Cardiovascular diseases include diseases related
to the heart and the blood circulatory system such as atherosclerosis,
arteriosclerosis, angina, hypertension, myocardial infarction (heart
attack) and stroke.

Health Issues Related to the
Human Circulatory System  10.6

10.6.1 10.6.2

Work in groups
and conduct a
case study on
the practices of
maintaining a healthy
human circulatory
system.

Activity Zone

• Atherosclerosis is the formation and deposition of plaque on the
artery walls.

• The plaque is formed from cholesterol, lipid, dead muscle tissues
and coagulated platelets.

• The plaque will clog and narrow the lumen in blood vessels.

• The restricted blood flow can cause hypertension.

• Hypertension causes fine arteries to break and the patient can suffer
from stroke if this happens in the brain.

• Stroke is also caused by blood clots (thrombus) that clog the flow
of blood in the brain.

• Atherosclerosis is the early stage of  arteriosclerosis.

• Arteriosclerosis occurs when calcium is deposited on the plaque
and causes the artery to become hard and lose its elasticity.

• If the lumen of the coronary artery (artery for the heart) is narrowed,
the insufficient oxygen supply to the heart muscles can cause
angina (severe chest pain).

• If the artery is completely clogged, myocardial infarction (heart
attack) will occur.

CARDIOVASCULAR DISEASES

Discuss a suitable
treatment for heart
failure.

Activity Zone

PHOTOGRAPH 10.6 Myocardial infarction (heart attack)

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What is the treatment for a patient who suffers from heart failure? What
are the risk factors that contribute to cardiovascular diseases and what
can we do to ensure that the cardiovascular system is healthy? Nanotechnology is

used in the diagnosis
and treatment of
atherosclerosis and
plaque formation
in arteries. In this
technique, nanoparticles
are designed to
resemble high-density
lipoprotein cholesterol
(HDL) (“good”
cholesterol) to help
reduce plaque.

STEM Bulletin

10.6.210.6.1

FIGURE 10.19 Formation and deposition of plaque on artery wall

dead cardiac
muscle tissues

Formative Practice 10.6
 1 What is the meaning of

myocardial infarction?

2 Explain how stroke happens.

3 In your opinion, what are the
factors that contribute to an
individual’s risk of getting
cardiovascular disease?

4 Explain how atherosclerosis
happens.

blood clot restricts the flow
of blood

artery

plaque is
formed in the
artery

coronary
artery

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10.7.1

oxygenated
blood at a high

pressure

arteriole

blood capillary

lymphatic capillary

deoxygenated
blood at a low
pressure

tissue fluid

blood plasma cell

Human Lymphatic System
The formation of tissue fluid
In addition to the blood circulatory system, there is one more system
in the body whose function is closely related to the blood circulatory
system. This system is called the lymphatic system. The formation of
tissue fluid is illustrated in Figure 10.20.

10.7
1 Blood that reaches the arterial end of the

blood capillary has a high pressure due to the
small diameter of capillaries and the pumping
force of the heart.

2 This pressure allows the blood
plasma to diffuse continuously
from the blood capillaries to the
intercellular space.

3 • Blood plasma that occupies the
intercellular space and constantly
bathes cells is called tissue fluid.

• The tissue fluid does not contain
any erythrocyte, platelet and
plasma protein because these
are too large to diffuse out of the
blood capillaries.

4 • Tissue fluid allows the exchange of
materials in the blood and cells to
occur.

• Nutrients and oxygen diffuse from
tissue fluid to body cells.

• Simultaneously, excretory products and
carbon dioxide diffuse from body cells
to blood capillaries through the tissue
fluid.

FIGURE 10.20 Exchange of substances between blood capillaries and body cells

Lymph formation and components of the lymphatic system
At the venule end of the blood capillary, blood plasma is hypertonic compared to the tissue fluid
surrounding it. Blood pressure is also lower. As a result, the reabsorption of water, mineral salts and
waste takes place in the venule capillary.

However, only 85% of the fluid that leaves the blood at the arteriole end of blood capillary diffuses
back into the venule end. What happens to the remaining 15% that is left in the intercellular space?
This remainder forms about 4 litres of fluid that is lost from capillaries each day. How does the blood
circulatory system regain this fluid?

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The lymphatic capillary wall consists of one layer of cells only. The lymphatic capillary differs from
blood capillary because one of its end is blocked or closed while the other end is connected to the
lymphatic  vessel (Figure10.21). Lymphatic capillaries found in intercellular spaces merge to form
a larger lymphatic vessel. Along the lymphatic vessel, there are lymph nodes at certain distances.

10.7.310.7.2

The lost fluid is collected and returned to the blood through the lymphatic capillary, which is the
smallest vessel in the lymphatic system. This fluid is known as lymph and is pale yellow in colour.
Table 10.7 and Table 10.8 show the similarities and differences between lymph with tissue fluid and
blood.

TABLE 10.7 Comparison between lymph and tissue fluid
Similarity

Both contain plasma without the plasma proteins, erythrocytes and platelets.

Differences

Lymph Tissue fluid

Higher content of fat and fat-soluble substances Low content of fat and fat-soluble substances

High content of lymphocytes Low content of lymphocytes

TABLE 10.8 Comparison between lymph and blood
Similarity

Both contain all the contents of plasma such as nutrients, hormones, enzymes, cellular wastes,
respiratory gases and leucocytes.

Differences

Lymph Blood

Does not contain plasma protein, erythrocyte and
platelet

Contains plasma proteins, erythrocytes and
platelets

FIGURE 10.21 Lymph formation

lymphatic
capillary

lymph

tissue
fluid

valve

arteriole

lymphatic  vessel

tissue
fluid

cell

venule

lymphatic capillary

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right lymphatic duct
tonsils

left subclavian
vein

right
subclavian
vein

spleen

appendix

lymph node

bone marrow

thoracic duct

lymphatic
vessel

thymus

The lymphatic system consists of organs such as lymph nodes, spleen, thymus gland, bone marrow,
tonsils and appendix (Figure 10.22). The lymphatic system does not have its own pump to circulate
the lymph along the lymphatic vessel. The flow of lymph is aided by heartbeat pulse, contraction of
skeletal muscles, peristalsis in the digestive tract and changes in pressure during inhalation and
exhalation of breath. In the lymphatic vessel, one-way valves ensure the lymph flows continuously
to the heart. These valves also prevent the lymph from flowing back.

Relationship between the blood circulatory system and the lymphatic system
All lymphatic vessels will eventually join with one of the two main lymphatic vessels which are the
thoracic duct dan right lymphatic duct  (Figure 10.22).

FIGURE 10.22 Lymphatic system
10.7.3

The right
lymphatic duct
receives lymph
from the right
hand, chest and
right side of the
head and neck.

The thoracic
duct receives
lymph from the left
side of the head,
neck and chest,
and all the body
parts below the
ribs.

lymph nodes

lymphocyte

valve
blood vessel

tissue fluid

lymphatic
capillary

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10.7.4

vein

Systemic circulation   Pulmonary circulation

FIGURE 10.23 Relationship between lymphatic system
        and blood circulatory system

FIGURE 10.24  The necessity of the
         lymphatic system

The thoracic duct will deliver its
contents into the left subclavian
vein while the right lymphatic duct
will transport lymph into the right
subclavian vein.

So the lymph collected from the whole
body will flow back into the blood
circulatory system. Figure 10.23 shows
the relationship between the lymphatic
system and the blood circulatory
system that complement each other.

right subclavian
vein

right lymphatic
duct

lymphatic
vessel

lymph
node

valve

lymph
node

lymphatic
capillaries

lymphatic
capillaries

systemic
capillaries

pulmonary
capillaries

artery

The necessity of the lymphatic system
The necessity of the lymphatic system is summarised in Figure 10.24.

COMPLEMENTS THE
BLOOD CIRCULATORY

SYSTEM

The lymphatic system returns
the excess tissue fluid in the
intercellular space into the
blood flow. The composition,
pressure and volume of blood are
maintained at a normal range.

BODY DEFENCE

Lymph nodes produce and store
lymphocytes that are involved in the
production of antibodies.

TRANSPORTATION OF FAT-
SOLUBLE SUBSTANCES

Fats and fat-soluble substances
diffuse into the lacteal in the villus
of the small intestine. Lacteals are
lymphatic capillaries. Lipid droplets
are transported to the thoracic
duct and blood circulatory system
through the left subclavian vein.

NECESSITIES OF
THE LYMPHATIC

SYSTEM

1 Name the two main lymphatic vessels.

2 State three main functions of the lymphatic
system.

3 State the differences between the composition
of blood plasma, tissue fluid and lymph.

4 After eating fatty food, the number of lipid
molecules in the lymph increases by 1%.
Explain why.

Formative Practice 10.7

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Have you ever wondered what would happen if our lymphatic system
does not function properly?  What would happen if the excess tissue fluid
is not returned to the blood flow? Tissue fluid that is not returned to the
blood circulatory system will accumulate in the intercellular space. This
will result in the swelling of the body tissues. This condition is known
as oedema (Photograph 10.7). Oedema may be caused by a number of
factors (Figure 10.25).

Health Issues Related to the
Human Lymphatic System 10.8

Why do our legs
swell after we sit for
too long?

Brainstorm!

PHOTOGRAPH 10.8
Swollen leg caused by
lymphatic filariasis

FIGURE 10.25 Causes of
oedema

10.8.1

PARASITIC INFECTION

• The parasite worm Brugia sp.
infects the lymphatic vessel
and prevents the flow of
lymphatic fluid.

• The infected part, for example,
leg will swell.

• The patient contracts
lymphatic filariasis (Photograph
10.8).

• This worm is transmitted
through mosquito bites.

DEFICIENCY IN
PLASMA PROTEIN

Deficiency of albumin
in the blood.

CAUSES OF
OEDEMA

1 How do parasitic infections happen?

2 Explain what would happen when the tissue
fluid fails to return to the blood circulatory
system.

3 Predict what would happen to the legs of a
patient who has been bedridden for a long
period of time? Explain your answer.

4 Lipid droplets or fat globules cannot diffuse
into the villus blood capillary but must diffuse
through the lacteal. Explain why.

Formative Practice 10.8

leg with oedemanormal leg

PREGNANCY

The body will produce more
body fluid to fulfill the needs of a
growing foetus.

PROLONGED BEDRIDDEN
PATIENTS

Paralysed or stroke patients with
limited mobility can suffer from
oedema in the legs.

PHOTOGRAPH 10.7
Oedema

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TRANSPORT IN HUMANS AND ANIMALS

Circulatory System Lymphatic System

Closed Circulatory System
Blood is contained in the
closed blood vessel that is
continuous and is distributed
to the whole body

Components of the
lymphatic system
• Lymph
• Lymphatic capillaries
• Lymphatic vessel
• Lymph nodes
• Lymphatic organs

The necessity of the
Lymphatic System
• Complements the blood

circulatory system
• Transportation of fat-

soluble substances
• Body defence

Health Issues Related to
the Human Lymphatic
System
• Lymphatic filariasis
• Parasitic infection
• Deficiency in plasma

protein
• Pregnancy
• Prolonged bedridden

patients

Fish
The fish heart has two
chambers: an atrium and a
ventricle

Amphibians
The heart of an amphibian
consists of three chambers:
two atria and one ventricle

Humans
The human heart consists
of four chambers: two atria
and two ventricles that are
completely separated

Circulatory
System of
Humans

• Blood
• Heart
• Blood vessel

Mechanism
of
Heartbeat

Mechanism
of Blood
Clotting

Health Issues
Related to Blood
Clotting

Open Circulatory
System
Haemolymph
flows into the
body cavities
(haemocoel) and
bathes cells

Insects
One or more hearts
pump haemolymph
through the
haemolymph vessel
into the haemocoel

Summary

• Thrombosis
• Embolism
• Haemophilia

• Blood type A
• Blood type B
• Blood type AB
• Blood type O
• Rhesus factor

Blood Groups of
Humans

• Arteriosclerosis
• Atherosclerosis
• Hypertension
• Angina
• Myocardial

infarction
• Stroke

Health Issues Related
to the Human
Circulatory System

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1 An accident victim with blood group B needs an immediate blood transfusion. Is it safe for
the patient to receive blood from individuals with the blood group O? Explain why.

2 An individual has a low number of erythrocytes. Explain the effect of this situation on his/her
health. Suggest the types of food that should be consumed by the individual to recover from
this situation.

3 The human heart has a pacemaker. The heart pacemaker that is damaged can be replaced
by an electronic pacemaker. Explain how the electronic pacemaker functions.

4 Name one example of nutrient found in blood and how the nutrient can be transported to
cells.

5 One of the lymphatic vessels of an individual is clogged.
  (a) Explain the effects on the lymphatic system of the individual.
  (b) Explain what will happen if the lymphatic vessel in the leg is clogged?

Have you mastered the following important concepts?
• The circulatory  system in a multicellular organism
• Components of the human circulatory system and to compare and contrast the types of blood

vessels
• Mechanism of the human heartbeat and the generation of force for blood circulation
• Mechanism of blood clotting
• The ABO blood system and Rhesus factor
• Health issues related to the circulatory system
• The formation of tissue fluid and lymph
• Describe components of the lymphatic system
• Health issues related to the lymphatic system

Self Reflection

Summative Practice 10

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6 Figure 1(a) shows a schematic of the blood circulatory system in humans and Figure 1(b)
shows the schematic of the blood circulatory system in fish.

Body

HEART

(a)

Head, neck, arm

Lungs

Gills Body

HEART

(b)

(a) Explain the blood circulatory system of fish.

(b) Based on Figure 1, compare the human and fish blood circulatory system.

(c) Explain the similarities between the two blood circulatory systems.

(d) Why does the blood flow in fish encounter more obstacles compared to the blood flow
in humans and explain how the fish can overcome this problem?

Essay Questions

7 Coronary heart disease is the main cause of death in our country. The following factors can
increase the risk of an individual contracting this disease:

• smoking
  • unbalanced diet
  • unhealthy lifestyle

Explain how these factors can contribute to coronary heart disease.

8 (a) Explain how the rhythmic contraction of heart muscles occurs.

(b) Ali’s leg feels numb after sitting cross-legged for an hour. Suggest the action to be
taken and give your reasons.

(c) Elly enjoys eating beef rendang and nasi lemak. Explain why this practice of eating in
the long term can affect her health.

FIGURE 1

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Enrichment

9 (a) A baby is born with a damaged bicuspid valve which cannot close tightly. Explain the
effect of this condition on the baby.

(b) A normal baby has a thick muscular heart wall that separates the left heart from the
right heart. If this muscle is not formed completely, predict the outcome on the quality of
blood that flows into the aorta.

10 How should an individual with a coronary artery that is clogged with cholesterol deposits be
treated?

11 Each year, thousands of people die from excessive blood loss caused by injuries during
accidents or war. One way to reduce the continuous outflow of blood from the injury is to
apply pressure on the wound with a bandage.  In your opinion, what adaptations can be
done to the bandage to make it more efficient in stopping blood loss temporarily until the
patient is admitted to the hospital?

Complete answers are
available by scanning the
QR code provided

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• What are the three lines of body defence in humans?
• How do antibodies react with antigens?
• What are the types of

immunity in humans?

Do you KNOW...

How do our bodies
fight bacteria and viral
infections?

CHAPTER

11 Immunity in
Humans

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11.1 Body Defence

11.1.1 Define:
  • immunity
  • antigen
  • antibody
 11.1.2 Describe the three lines of body

defence in humans:
  • the first line of defence:

– physical
   – chemical
  • the second line of defence:

– fever
   – inflammation

– phagocytosis
  • the third line of defence:

– antibody
   – memory cell

11.2 Actions of Antibodies

11.2.1 Discuss the actions of antibodies
on foreign antigens:

• neutralisation
  • agglutination
  • precipitation
  • opsonisation
  • lysis

11.3 Types of Immunity

11.3.1 Communicate about the types of
immunity:

• passive immunity
  • active immunity
 11.3.2 Compare and contrast passive

immunity and active immunity

11.4 Health Issues Related to Immunity

11.4.1 Describe health issues related
to Acquired Immuno Deficiency
Syndrome (AIDS).

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You may recall learning about the body defence system in Form 2. The
body defence system reacts when pathogens infect the body. A pathogen
is a microorganism that causes diseases. Examples of pathogens include
bacteria (singular: bacterium), viruses and parasites. Pathogens can only
cause diseases if they successfully infect body cells.

The body defence system recognises pathogens as foreign particles
known as antigens. Antigens are foreign particles that enter the body
and subsequently stimulate the immune response.

Antigens stimulate the lymphocytes to produce antibodies into the
blood flow to destroy the antigens. Antibodies are proteins found on
the lymphocyte surface or proteins released by lymphocytes into
the blood plasma. The interaction between antibodies and antigens
that cause antigens to be destroyed is called the immune response
(Figure 11.1).

Immunity is the body’s ability to fight
infections caused by pathogens or other
foreign objects, through specific attacks
on the pathogens.

When our body can fight a disease, we
are said to be immune to that disease.

There are three lines of defence to
fight against diseases in our body:
• The first line of defence
• The second line of defence
• The third line of defence

The first line of defence
The first line of defence consists of
the physical and chemical line-up
that prevent pathogens from entering

the body. The first line of defence is the defence line that is not
specific and acts to prevent pathogens from entering the body.
Figure 11.2 shows the organs and mechanisms involved in the first line
of defence.

Body Defence  11.1

11.1.211.1.1

FIGURE 11.1 Interaction between antibodies and
antigens

antibody
antigen

List the physical and
chemical defences
found in the first line
of defence.

Activity Zone

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Hydrochloric acid in the stomach destroys bacteria
present in food and drinks.

HYDROCHLORIC ACID

Lysozyme found in the secretion of tears,
nasal mucus and saliva, is an antimicrobial
protein that can dissolve and destroy some

types of bacteria.

LYSOZYME

FIGURE 11.2 The first line of defence

MUCOUS MEMBRANE

The mucous membrane that lines
the respiratory tract secretes a
sticky fluid called mucus. Mucus
contains lysozyme that destroys
bacteria found in the air that
enters the respiratory system.

11.1.2

The blood clotting mechanism prevents bacteria from
entering through wounds.

MECHANISM OF BLOOD CLOTTING

• It is the physical defence that prevents the entry of pathogens because it is tough and is difficult for
microorganisms to penetrate.

• The continuous shedding of dead cell layers on the skin surface makes it difficult for various types of
microorganism to grow.

• Acts as a chemical shield through the secretion of sebum. Oil and acid in the sebum prevent the
growth of various types of microorganisms.

• Sweat secreted by the skin contains lysozyme, a type of enzyme that breaks down the cell wall of
some bacteria.

SKIN

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FIGURE 11.3 The phagocytosis stages

bacterium

phagocyte

lysozyme

lysosome
phagosome

phagolysosome

bacterium decomposes

Phagocyte extends its pseudopodium
towards the bacterium and envelops the
bacteria

1

Bacterial ingestion
forms phagosome2

Phagosome combines with
lysosome that secretes lysozyme
into the phagosome

3

Bacterium in the phagosome
is destroyed by the
lysozyme

4

Phagocyte expels the
remains of the digested
microorganism out of
the cell

5

The second line of defence
• The second line of defence is fever, phagocytosis

and inflammation.
• The mechanism of the second line of defence is also not specific.

Fever
Fever is the second line of defence mechanism that fights infections.
Fever increases phagocytic activity and fights against microorganisms
that infect the body.

Phagocytosis
• The phagocyte is a leucocyte that can carry out phagocytosis.

Neutrophils and monocytes are phagocytes.
• Phagocytosis is the process by which microorganisms or

other particles such as dead cells are trapped and digested by
phagocytes.

• When an infection occurs, the phagocytes move to the infected area
and enter the tissue fluid through the pores of the capillary wall.

• When a phagocyte encounters a pathogen, the phagocyte will
engulf the pathogen and the lysozyme in the phagocyte will digest
the pathogen (Photograph 11.1).

• The stages of phagocytosis are summarised in Figure 11.3.

PHOTOGRAPH 11.1 The
electron micrograph shows
a phagocyte extending its
pseudopodium to engulf
bacteria

11.1.2

ICT 11.1

Video: Phagocytosis
(Accessed on 21 August 2019)

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Inflammation
Inflammation is the immediate response that destroys and
neutralises harmful actions of microorganisms and toxins at the early
stages of infection. The inflamed area will swell, turn red and feel
painful. The response to inflammation is described in Figure 11.4.

The third line of defence
If pathogens overcome the second line of defence, the third
line of defence will be activated. The third line of defence is the
immune response  of the lymphocytes.
• The lymphocytes formed in the lymph nodes produce

antibodies.
• The actions of antibodies are specific. Each type of antibody

can only combine with a certain type of antigen (Figure 11.5).
• When a person is infected with pathogens, a large number of

lymphocytes will accumulate in the lymph nodes to destroy the
antigens and foreign particles. This will cause the lymph nodes to
swell.

• The lymph nodes also contain macrophages that destroy bacteria, dead
tissues and foreign particles through phagocytosis.

• Lymphocytes are divided into two types, T lymphocytes and
B lymphocytes.

• The T lymphocyte attacks cells infected by pathogens. T lymphocytes
stimulate B lymphocytes to produce memory cells.

• If the same pathogen attacks, the memory cells will be stimulated to
produce antibodies immediately.

FIGURE 11.5 The antigen
molecule will combine
with the antigen receptor
site found in the antibody
molecule

phagocyte

bacterium

histamine

infected area
skin

platelets

Biological Lens

Pus is a combination
of microorganisms,
fragments of tissues
and white blood cells
that can be found in
seriously infected areas
or damaged tissues.

11.1.2

The damaged tissue releases
histamine. Histamine will
stimulate an immediate
inflammatory response.

1

• Histamine will cause the blood
capillaries to expand for more
blood to flow to the infected
area.

• Histamine also increases
the permeability of blood
capillaries to phagocytes.

• The phagocytes and clotting
factors will accumulate in the
infected area.

2

The blood clotting
mechanism is triggered.

3

The phagocytes carry out
phagocytosis.

4

FIGURE 11.4 Inflammatory responseFIGURE 11.4 Inflammatory response

antibody

antigens

antigen receptor
site

lymphocyte
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Antigens are destroyed by antibodies through several mechanisms as
illustrated in Figure 11.6.

Actions of Antibodies11.2

Antibodies bind with toxins produced by bacteria
and neutralise the toxin.

NEUTRALISATION

Antibodies coagulate the
pathogens and make them an
easy target to be trapped and
destroyed by phagocytes.

AGGLUTINATION
antibody

antigen

Formative Practice 11.1
 1 What is the meaning of immunity?

2 Name two characteristics of the skin that
  allows the skin to react as an effective first

line of defence.

3 How does the phagocyte destroy
pathogens that have penetrated the first line
of defence?

4 Differentiate between antigens and antibodies.

toxinantibody

Antibodies react with dissolved antigens
to form an insoluble complex
(precipitate) that is easily destroyed
by phagocytes.

PRECIPITATION

11.2.1

precipitation of
antigen molecules

antibody

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The Ministry of
Health (MOH)
recommends that
babies aged
2 to 3 months
be immunised
against diseases
such as diphtheria,
pertussis, tetanus,
poliomyelitis
and meningitis.

Our World of Biology

Types of Immunity11.3  There are two types of immunity: active immunity and passive
immunity. Active immunity means that lymphocytes produce their
own antibodies as a response to stimulation by the antigens. Passive
immunity means that the body receives antibodies from an external
source. Both of these types of immunities can be naturally or artificially
acquired.

opsonin antibodies
combine with
antigens

Antibodies combine with antigens and
cause bacteria to be broken down and
decomposed.

LYSIS

Antibodies combine with antigens and act as a marker
for phagocytes to recognise the antigens and destroy
them.

OPSONISATION

FIGURE 11.6 Action of antibodies on antigens

antigen
bacterium

11.3.1

antigen
bacterium

• Natural active immunity
Acquired after an individual
recovers from an infection

• Artificial active immunity
Acquired when an individual is
given a vaccine injection

• Natural passive immunity
Acquired through breastfeeding
and from the mother to the
foetus during pregnancy

• Artificial passive immunity
Acquired through an antiserum
injection

ACTIVE IMMUNITY PASSIVE IMMUNITY

IMMUNITY

bacterium undergoes lysis
(decomposition)

lysine antibody combines
with antigen

antigen

baterium

phagocyte traps the bacterium
that has been identified by the
antibody marker

antigenbacterium

nucleus

antibody

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• When someone is infected by pathogens,
lymphocytes will produce antibodies as
a response to these antigens.

• When an individual recovers from an
infection, that individual will gain a
permanent immunity against the disease.

• When the individual is attacked again by
the same pathogen, the lymphocytes that
stored memories of the pathogen, that
is, memory cells will rapidly produce
antibodies to react immediately against
the antigens.

Active immunity and passive immunity
Let us examine active immunity and passive immunity in greater detail.

• To protect oneself from being infected by
a highly infectious disease, an individual
can be immunised against the disease.

• Immunisation refers to the process that
stimulates immunity against a specific
disease through vaccine injections.

• Vaccine is a suspension of pathogens
that are weakened, dead or non-virulent.

• When a vaccine is injected into the body,
the vaccine will stimulate lymphocytes
to produce antibodies to fight the
pathogens.

• The first vaccine injection will usually
result in a low level of antibody
production which is insufficient to protect
an individual from the disease. A booster
dose must be administered to increase
the antibody production to a level of
immunity that can protect the individual
from the disease.

• If the individual is infected by actual
pathogens, the lymphocytes will produce
enough antibodies and immediately
destroy these pathogens.

• Examples of vaccines are the Salk
vaccine for poliomyelitis, BCG vaccine

(Bacille Calmette-Guerin) for
tuberculosis (TB) and HPV

vaccine for cervical cancer.

Why are only female
pupils given the HPV
vaccination (Human
papillomavirus)?

Brainstorm!

• Antibodies are produced naturally by lymphocytes.

• Active immunity remains for a long period of time.

ACTIVE IMMUNITY

NATURAL ACTIVE IMMUNITY ARTIFICIAL ACTIVE IMMUNITY

11.3.1

PHOTOGRAPH 11.2 An individual who has
recovered from chickenpox or influenza has gained a
natural active immunity

PHOTOGRAPH 11.3 Immunisation
protects a person from being
infected by infectious diseases

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• This immunity is acquired by a foetus
when the mother’s antibodies diffuse
through the placenta into the blood flow
of the foetus.

• Antibodies also protect the baby for
the first few months after birth through
antibodies that are found in the mother’s
milk or colostrum when breastfeeding.

• This immunity is acquired through an
antiserum injection or serum that
contains specific antibodies to fight
specific antigens.

• The antiserum injection gives immediate
protection but only for a short period of
time.

• Examples of antiserum are antitetanus,
anti-rabies and antiserum for poisonous
snakes.

11.3.1

• The body does not produce its own antibodies.

• Antibodies are obtained from an external source.

• Passive immunity does not persist and can only give immediate, short-
term and temporary protection.

PASSIVE IMMUNITY

NATURAL PASSIVE IMMUNITY ARTIFICIAL PASSIVE IMMUNITY

Injected in
a horse

The antitetanus
from the horse
serum is
concentrated and
purified

Tetanus toxoid
suspension

Injected into individuals
with high risk of tetanus

The individual
is protected from
tetanus infection

FIGURE 11.7  Antitetanus preparation

PHOTOGRAPH 11.4 Babies gain natural
passive immunity from the mother’s milk

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Similarities

• Protects the body from infectious diseases
• Involves interaction between antibodies and antigens

Differences

Aspect Artificial Active Immunity Artificial Passive Immunity

Acquired
through

Vaccine injection Antiserum injection

Injected
substance

Vaccine is a suspension of pathogens
that are weakened, dead or non-virulent.

Antiserum is a serum that contains
specific antibodies.

Purpose Prevention Treatment or when immediate
protection is required

Effect Does not give immediate protection Gives immediate protection

Immunity
period

Immunity lasts for a long period of time Immunity is temporary and does not
persist

When
injection is
given

Vaccine injection is administered before
being infected

Antibody injection is given in advance
if there is a high risk of infection or
immediately after being infected by a
disease

Antibody Antibodies are produced by the
lymphocytes

Antibodies are obtained from
antiserums

The need to
give a second
injection
(booster
dose)

Must be given to boost the level of
antibodies above the level of immunity as
a protection against the disease

Is only given when the antibody level
in the blood drops below the level of
immunity and the patient is still infected
by the disease

11.3.2

0 42 6 8

20

40

60

antibody level in blood
(arbitrary units)

time
(month)

level of immunity

first
injection

second
injection

FIGURE 11.8 The antibody level in the blood of a
person after the first and second vaccinations

the immunity level refers
to the concentration of
antibodies that is sufficient
to fight the disease

0 42 6 8

20

40

60

antibody level in blood
(arbitrary units)

time
(month)

level of immunity

first
injection

second
injection

FIGURE 11.9 The antibody level in the blood of
a person after the first and second antiserum
injections

TABLE 11.1 Comparison between artificial active immunity and artificial passive immunity

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11.4.1

Health Issues Related to
Human Immunity
Acquired Immunodeficiency Syndrome
(AIDS)
The human immunodeficiency virus (HIV) is a virus that attacks
the human immune system. HIV infection causes Acquired
Immunodeficiency Syndrome (AIDS).

An AIDS patient is easily infected by other diseases because of the
progressive destruction of the individual’s immune system. HIV
spreads in the lymphocyte and destroys the lymphocyte (Photograph
11.5).

An individual infected with HIV does not show any symptoms for the
first few years although HIV has been actively attacking the immune
system. Symptoms of the disease include chronic diarrhoea and fungi
infection which are only visible after 8 to 10 years. Since the immune
system of the individual is already weakened, the body can be easily
infected by diseases. Finally, the immune system is paralysed and the
patient will die from other infections.

HIV transmission
HIV enters the body through the transfer of
body fluids such as blood and semen or
across the placenta. Women infected
with HIV can transfer the virus to
the baby during pregnancy, birth or
breastfeeding.

11.4

Millennial Career

Immunologists
are specialists in
allergy diseases
and diseases that
involve the immune
system.

Millennial Career

PHOTOGRAPH 11.5  HIV attacks lymphocyte

1 What are the types of immunity that
decrease according to time? Explain why.

2 Propose immediate treatment that can be
given to someone who has been bitten by a
poisonous snake.

3 State one difference between artificial
passive immunity and artificial active
immunity.

4 In your opinion, why must we follow and
complete the immunisation plan in Malaysia?

Formative Practice 11.2

HIV is able to mutate
and change the cell
structure when it
spreads. This gives the
virus a high resistance
to drug therapy.

Biological Lens

HIV

lymphocyte

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Activities2.1 Conducting a research study on issues
related to the human immune system

Activity 11.1

Materials
Medical magazines and the Internet

Procedure
 1 Conduct a research study with a friend on:

• Systemic Lupus Erythematosus (SLE) • Allergy

2 Discuss your findings with friends from other groups and present the findings of each group.

11.4.1

Research
study

1 What is the meaning of AIDS?

2 Explain how HIV infection can
cause someone to suffer from
AIDS.

3 Why is a person who is
infected with HIV, may not
necessarily suffer from AIDS?

4 How can AIDS be prevented?

Formative Practice 11.3

Nevertheless, HIV infection in the foetus and newborn baby can be
avoided with proper medical treatment when the mother is pregnant
and during birth.

Individuals can be infected by HIV through unprotected sexual relations
with an infected individual. They can also be infected when they share
contaminated needles used to inject drugs or tattoo ink. In addition,
HIV  is also spread through HIV-infected blood transfusion.

There are a few types of diseases and conditions related to the immune
system. Conduct the following research study activity to find out more.

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The first line of
defence
• Physical
 –  Skin
• Chemical
 – Sebum
 – Sweat
 – Lysozyme
 – Mucous membrane
 – Hydrochloric acid
 – Mechanism of

blood clotting
The second line of
defence
• Fever
• Inflammation
• Phagocytosis
The third line of
defence
• Antibody
• Memory cell

Active immunity
• Active natural immunity (when someone is infected by

pathogens, lymphocytes will produce antibodies as a
response to the antigen)

• Artificial active immunity (a process that stimulates immunity
through vaccine injection)

Passive immunity
• Passive natural immunity (acquired by the foetus in the

mother’s womb and during breastfeeding)
• Artificial passive immunity (serum injection that contains

antibodies that fight against certain antigens)

• Neutralisation
• Agglutination
• Precipitation
• Opsonisation
• Lysis

• Acquired
Immunodeficiency
Syndrome (AIDS)

• Systemic Lupus
Erythematosus (SLE)

• Allergy

Body Defence Actions of
Antibodies

Types of
Immunity

Health Issues
Related to Human

Immunity

IMMUNITY IN HUMANS

Have you mastered the following important concepts?
• Definition of immunity, antigen and antibodies
• The first, second and third lines of defence in a human body
• Antibody action on antigen
• Active and passive immunities
• Health issues related to human immunity

Summary

Self Reflection

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Summative Practice 11
 1 Suggest an immediate treatment to an individual bitten by a very poisonous snake.

2 Explain how a mother who has HIV can infect a foetus in her womb.

3 (a) State the type of immunity a foetus receives from its mother.
  (b) Explain how the placenta helps in the immune system of the foetus.

4 Figure 1 illustrates the changes in the antibody levels in the blood of individuals X and Y for a
specific period of time.

the antibody level
in blood

time
(weeks)

level of immunity

first injection

Individual X

the antibody level
in blood

time
(weeks)

level of immunity

first injection

Individual Y

the antibody level
in blood

time
(weeks)

level of immunity

first injection

Individual X

the antibody level
in blood

time
(weeks)

level of immunity

first injection

Individual Y

FIGURE 1
  (a) (i) What type of immunity did individuals X and Y acquire?
   (ii) State the substance injected in individuals X and Y.
   (iii) Explain the differences in the content of the substances you mentioned in (a)(ii).

(b) (i) On the graph curves of individuals X and Y, mark with an arrow, the time of the
second injection is given.

(ii) Why do individuals X and Y need a second injection?
   (iii) Based on the graph curves for individuals X and Y, state two differences in the

immunity achieved by individuals X and Y.

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Essay Questions

5 Two individuals acquired immunity against chickenpox in different situations. Individual
X recovered from chickenpox. Individual Y was injected with a type of suspension and
received immunity against chickenpox after a few months.

Explain the immunity acquired by
  (a) individual X
  (b) individual Y

6 (a) A newborn baby needs to receive immunisation based on the Immunisation Plan
recommended by the World Health Organisation (WHO).

Explain why the immunisation programme is required.

(b) (i) Some vaccine injections require only one dose throughout the lifetime of an
individual. Explain why.

(ii) Sinti’s mother forgot to bring Sinti to the clinic for the third dosage of the hepatitis
vaccination. Explain the effects on Sinti’s immunity.

(iii) Aziman accidentally stepped on a rusty nail during a mountain climbing expedition.
 Describe the type of injection that is suitable to be administered by the doctor.
 Explain your answer.

(c) Explain how HIV can paralyse the immune system of a person infected by the virus.

Enrichment

7 Sometimes doctors prescribe antibiotics to treat some infectious diseases. Doctors will
advise taking all the antibiotics prescribed for the recommended period. Explain why it is
important to follow this step.

8 You visited a sick friend in a hospital. MRSA (methicillin-resistant Staphylococcus aureus) is
a strain of bacteria that is usually found in hospitals. This bacterial strain is immune to many
types of antibiotics due to the numerous types of antibiotics used to treat patients in the
hospital. Suggest steps that you can take to prevent the infection of MRSA.

Complete answers are
available by scanning the
QR code provided

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12.1  Coordination and Response

12.1.1 Make a sequence and
describe the components in
human coordination:

•  stimulus  •  effector
  •  receptor  •  response
  •  integration centre
12.1.2 Identify and describe external

and internal stimuli.

12.1.3 List the types of sensory receptors
based on the stimuli involved:

• chemoreceptor
 • mechanoreceptor
 • photoreceptor
 • thermoreceptor
 • baroreceptor
 • nociceptor
12.1.4  Justify the necessity to respond to

external and internal stimuli.

Sophia
Robot

Can robots function
fully like humans in the
future?

Coordination
and Response
in Humans

CHAPTER

12

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12.2 Nervous System
12.2.1 Construct an organisational chart

and explain the structures of the
human nervous system:

• central nervous system
  – brain       – spinal cord
 • peripheral nervous system
  – sensory receptor
  – cranial nerve
  – spinal nerve
12.2.2 Explain the functions of parts of the

central nervous system related to
coordination and response:

•  brain
  – cerebrum       – hypothalamus
   – cerebellum     – pituitary gland

– medulla oblongata
• spinal cord

12.2.3 Communicate about the functions
of parts of the peripheral nervous
system in coordination and
response.

12.3 Neurones and Synapse
12.3.1 Draw and label structures of a

sensory neurone and a motor
neurone:

• dendrite        •  myelin sheath
 • axon        •  node of Ranvier
 • cell body
12.3.2 Analyse the functions of each type

of neurone in impulse transmission.
12.3.3 Explain the structure and function

of synapse.
12.3.4 Explain the transmission of impulse

across a synapse.

12.4 Voluntary and Involuntary Actions
12.4.1 Compare and contrast voluntary

and involuntary actions.
12.4.2 Describe the reflex actions

involving:
 • two neurones
 • three neurones
12.4.3 Draw a reflex arc.

12.5 Health Issues Related to the Nervous
System
12.5.1 Communicate about the health

issues related to the nervous
system.

12.5.2 Describe the effects of drug
and alcohol abuse on human
coordination and response.

12.6 Endocrine System
12.6.1 State the role of endocrine glands

in humans.
12.6.2 Identify and label the endocrine

glands in humans.
12.6.3 Analyse the functions of hormones

secreted by each endocrine glands:
 • hypothalamus
  – gonadotrophin-releasing

hormone (GnRH)
 • the anterior lobe of pituitary
  – growth hormone (GH)

– follicle-stimulating hormone
        (FSH)

– luteinizing hormone (LH)
  – thyroid-stimulating hormone

(TSH)
  – adrenocorticotropic hormone

(ACTH)
 • the posterior lobe of pituitary

– oxytocin hormone
  – antidiuretic hormone (ADH)
 • thyroid – thyroxine hormone
 • pancreas
  – insulin hormone
  – glucagon hormone
 • adrenal
  – adrenaline hormone
  – aldosterone hormone
 • ovary
  – oestrogen hormone
  – progesterone hormone
 • testis
  – testosterone hormone
12.6.4 Discuss involvement of the nervous

system and endocrine system in a
“fight or flight” situation.

12.6.5 Compare and contrast the nervous
and the endocrine system.

12.7 Health Issues Related to the Endocrine
System

12.7.1 Predict the effects of hormonal
imbalances on human health.

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Organisms have the ability to detect changes in their environments
and respond to these changes. This ability is called sensitivity while
the change that stimulates the response is known as a stimulus (plural:
stimuli). The stimulus is divided into two types, that is, external stimulus
and internal stimulus.
 (a) Stimuli from the external environment include light, sound

smell, taste, surrounding temperature, pressure and touch.
 (b) Stimuli from the internal environment include changes in

blood osmotic pressure, changes in body temperature and
 changes in blood sugar level.

Mammals can detect stimuli via the special sensory cells known as
receptors. When a receptor detects a stimulus such as sound, the
stimulus is converted to nerve impulses. Nerve impulses are sent to the
brain through nerve cells or neurones. The brain is the integration centre
that translates nerve impulses and coordinates an appropriate response.
Response refers to the way organisms react after detecting a stimulus.
The part of the body that responds is called the effector. Examples of
effectors are muscles and glands. Figure 12.1 and Figure 12.2 explain the
main components and pathways involved in detecting and responding
to changes in external and internal environments.

Coordination and Response  12.1

Impul
ses

are
 se

nt t
hro

ugh
 the

moto
r ne

uro
ne

to t
he

effe
cto

r

Stimulus from the external environment
(example: the sound of phone ringing)

Detected by sensory
receptors in the sensory
organs and transformed into
nerve impulses

In the integration centre (the brain),
nerve impulses are interpreted and
a response is triggered

Nerve
 im

pulses a
re se

nt

through the se
nsory n

eurone

to the integration ce
ntre

Effector (hand muscles)
produces a response
(answering the telephone)

FIGURE 12.1 Main components and pathways involved in detecting and
responding to changes in the external environment

12.1.1 12.1.2216

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Stimulus from
the internal
environment
(example: blood
pressure increases
during running)

Detected by receptors
(baroreceptor) in the aortic
arch and carotid artery

Integration centre
(cardiovascular
control centre in the
medulla oblongata)

The effectors
react (weakened
contraction of cardiac
muscles and the
expansion of blood
vessels’ diameter)
to reduce the blood
pressure to the
normal range

FIGURE 12.2 The main components and pathways involved in detecting
and responding to changes in the internal environment

Nerve impulses
are sent through
the sensory
neurone to the
integration centre

The cardiovascular
control centre sends
nerve impulses through
the motor neurone to
the effectors

12.1.1 12.1.2

Conduct a role play
activity to explain
coordination and
responses.

Activity Zone

Receptors and effectors work together to bring suitable changes
depending on the stimulus detected.
Coordination is a stimuli detection process by receptors that ends in
appropriate responses by effectors. Coordination ensures that the overall
activities and systems of an organism function and are synchronised
perfectly as a complete unit. The role of coordination and response is
conducted by two separate systems, that is, the nervous system and the
endocrine system.
Both systems work together to coordinate and control responses.

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Types of receptors
Sensory receptors found at the end of the nerve fibres detect information
in the external and internal environments. The location of receptors will
depend on the type of stimulus detected. Each type of receptor is usually
sensitive to a specific stimulus. For example, the sensory receptors that
detect external stimuli are found in special sensory organs such as eyes,
nose, tongue and skin. The sensory receptors that detect internal stimuli
are present in specific internal organs such as the pancreatic cells that
detect blood sugar level.

FIGURE 12.3 Detection of external stimulus by the photoreceptor

All receptors can
be considered as
energy converters,
that is, receptors can
convert one form of
energy into another.
For example, the
eye photoreceptor
converts light energy
into electrical signals,
which is a form
accepted by the
nervous system.

Across the fields

integration centre
(the brain)

light stimulus

receptor (photoreceptor)

12.1.3

TABLE 12.1 Types of sensory receptors and stimulus involved
Sensory receptor Stimulus

Photoreceptor Light

Thermoreceptor Change in temperature

Chemoreceptor Chemical substances

Baroreceptor Change in pressure

Mechanoreceptor Touch and pressure

Nociceptor Pain

sensory neurone
(optic nerve)

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Necessity of response
Why do organisms have to respond to stimuli and internal
stimuli? The ability of organisms to detect changes in the
external environment and its response to the stimuli is very
important for the survival of organisms. For some animals, a
sudden change in climate conditions motivates the animals to
look for new shelters.
The ability of organisms to detect changes in the internal
environment is also crucial so that the information can be
transmitted to the integration centre. The integration centre
will then transmit this information to the effectors to respond
to the changes. For example, when the body temperature
increases above the normal range, this information will
be transmitted to the integration centre by a receptor. The
integration centre will send nerve impulses to the effectors
to decrease the temperature back to its normal range. In
conclusion, humans and animals need to respond to adapt to
the changes in the environment.

PHOTOGRAPH 12.1 Animals migrate when they
sense changes in the climate

12.1.4

PHOTOGRAPH 12.2
A fast  response is
necessary to save a
goal

1 What is the meaning of response?

2 Which sensory organ has the
mechanoreceptor as a sensory receptor?

3 In your opinion, why is coordination crucial
to humans?

4 You feel a mosquito bite on your leg and
you hit it. Desribe the pathway involved in
detecting and responding to the stimulus of
the mosquito bite.

12.1Formative Practice

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Nervous System
The human nervous system is made up of a network of nerve cells or
neurones. This system is divided into two main subsystems: the central
nervous system and the peripheral nervous system (Figure 12.4).
The central nervous system includes the brain and spinal cord. The
peripheral nervous system consists of 12 pairs of cranial nerves and 31
pairs of spinal nerves. The cranial nerves send nerve impulses from and
to the brain. Spinal nerves send nerve impulses from and to the spinal
cord.

12.2

FIGURE 12.4 A schematic diagram showing
the organisation of the human nervous
system

PERIPHERAL
NERVOUS
SYSTEM

brain

spinal
cord

spinal
nerve

sensory
receptor

cranial
nerve

12.2.1

CENTRAL
NERVOUS
SYSTEM

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AR

FIGURE 12.5 Human brain

12.2.2

Brain
Do you know that the brain is made up of more than 100 billion neurones?
The brain is the coordination and control centre for humans. The main
components of the brain are the cerebrum, hypothalamus, cerebellum,
medulla oblongata and pituitary gland (Figure 12.5).

spinal
cord

HYPOTHALAMUS

• Coordinating homeostasis.

• It is the control centre that
regulates body temperature,
water balance, blood
pressure, and senses hunger,
thirst and fatigue.

• The hypothalamus connects
the nervous system to the
endocrine system through the
pituitary gland.

• Controls the secretion of a
few types of pituitary gland
hormones.

CEREBRUM

Maintains body
balance and
coordination of
muscle contraction
for body
movement.

CEREBELLUM

• Located at the anterior of the cerebellum.

• Controls involuntary actions such as
heartbeat, breathing, food digestion,
vasoconstriction, blood pressure,
peristalsis, vomiting, coughing, sneezing
and swallowing.

MEDULLA OBLONGATA

• The largest and most complex structure present in the frontal part of the brain.

• The surface is folded to increase the surface area to hold more nerves.

• It is the centre that controls emotions, hearing, sight, personality and controlled actions.

• The cerebrum receives information and stimulus from the receptor.

• This information is analysed, integrated and correlated to produce sensory perception.

• The response is determined and instructions are given to the effectors.

• The cerebrum is also responsible for higher mental abilities such as learning, memorising, linguistic
skills and mathematics skills.

• Located at the base of the
hypothalamus.

• The main gland in the endocrine system.

• This gland secretes hormones that
control the secretion of hormones by
other endocrine glands.

PITUITARY GLAND

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12.2.312.2.2

Spinal cord
The spinal cord is contained within the vertebral column and is
surrounded by cerebrospinal fluid that protects and supplies the spinal
cord with nutrients. The spinal cord is made up of white matter and
grey matter (Figure 12.6). In a cross section, the grey matter looks like
a butterfly or the letter ‘H’. Grey matter comprises mainly of cell bodies
and is surrounded by white matter. White matter consists of axons
covered in myelin sheath and extends up and down the spinal cord. The
spinal nerve extends from the spinal cord through two short branches
or roots which are the dorsal root and ventral root.
The function of the spinal cord is to
(a) process a few types of sensory information and to send
 responses through the motor neurones
(b) control reflex action
(c) connect the brain with the peripheral nervous system
The detailed functions of the spinal cord structure is summarised in
Figure 12.6.

DORSAL ROOT

In a newly operated
section of the spinal
cord, the white
matter appears
white and the grey
matter appears
grey. Can you
explain why?

Brainstorm!

FIGURE 12.6 Cross section showing the detailed structure of the spinal cord, white matter and grey matter

motor
neurone

grey matter

white matter (contains
myelin-coated axon)

relay neurone

sensory
neurone

The dorsal root contains the axon
of the sensory neurone that sends
nerve impulses from the sensory
receptor to the spinal cord.

VENTRAL ROOT

The ventral root contains the motor neurone that sends
nerve impulses from the spinal cord to the effector.

SPINAL NERVE

The spinal nerve contains
the sensory neurone and
motor neurone.

DORSAL ROOT GANGLION

The sensory neurones’ cell bodies are
clustered in the dorsal root ganglion

Peripheral nervous system
The peripheral nervous system consists of the somatic nervous system and autonomic nervous
system. The somatic nervous system regulates all controlled actions. The autonomic nervous system
controls involuntary actions such as heartbeat and contraction of the blood vessel. The function of
the peripheral nervous system is to connect sensory receptors and effectors to the central nervous
system.
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A person suffering
from a stroke is
having difficulty in
moving his left hand.
Which part of the
brain is damaged?

Brainstorm!

Neurones and Synapse
The nervous system is made up of millions of nerve cells known
as neurones. The basic structure of a neurone consists of a cell
body, axon, dendrite, myelin sheath, a node of Ranvier and a
synaptic knob (Figure 12.7). There are three types of neurones
which are sensory neurones, relay neurones and motor neurones
(Figure 12.8).

12.3

FIGURE 12.7 The basic
structures and functions of the
the parts of the neurone

12.3.1 12.3.2

DENDRITE

Dendrites are short branches
of the cell body. Dendrite
receives nerve impulses from
other neurones or the external
environment and sends them to
the cell body.

AXON

Axon is an elongated branch
of the body cell. Axon carries
impulses out of the cell body to
other neurones or effectors.

NODE OF RANVIER

Certain neurones have parts that
are not insulated by the myelin
sheath at regular gaps along
the axon. This gap is known as
a node of Ranvier. The node
of Ranvier helps to accelerate
the flow of nerve impulses by
allowing the nerve impulses
to jump from one node to the
following node.

direction
of impulse
flow

1 Explain the role of the brain in
body coordination.

2 Compare the functions of the
cerebellum and the medulla
oblongata.

3 State one difference between
the functions of the somatic
nervous system and the
autonomic nervous system.

4 Explain why we cannot resist
sneezing.

12.2Formative Practice

CELL BODY

A cell body consists of a nucleus
and many cytoplasmic projections
called dendrites. The cell body
integrates signals and coordinates
metabolic activities.

Myelin sheath is an insulating
membrane that coats the axon.
Function of the myelin sheath:

• protects neurones from
injury

• functions as an insulator for
electrical impulses

• provides nutrients to the
axon

MYELIN SHEATH

SYNAPTIC KNOB

The synaptic knob is a swelling
at the end of the axon branch.
The synaptic knob sends signals
to muscle cells, gland cells or
other neurone dendrites.

muscle
cells

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FIGURE 12.8 Types and functions of neurones

• Present in the dorsal root of the spinal
nerve.

• Carries nerve impulses from the
sensory organ receptors to the
central nervous system.

• The cell body is found in the dorsal
root ganglion.

• Dendrites receive nerve impulses from
receptors and send them to the cell
body.

• The nerve impulses are transferred from
the cell body through the axon to the
next neurone.

• Can be found in the ventral root of
the spinal nerve.

• Receives nerve impulses from
the relay neurone of the central
nervous system and sends nerve
impulses to effectors such as
muscles or glands to produce the
appropriate response.

• The cell body is present in the grey
matter of the spinal cord.

• Nerve fibres found in the central
nervous system.

• Connects the sensory neurone to
the motor neurone.

• The cell body can be found in
clusters in the grey matter of the
central nervous system.

• Sends nerve impulses from the
sensory neurone to the central
nervous system and from the
central nervous system to the motor
neurone.

SENSORY NEURONE

MOTOR NEURONE

RELAY NEURONE

12.3.312.3.2

cell
body

dendrite
nucleus axon

direction of impulse flow
synaptic
knob

Structure and functions of synapses
Information is sent along the neurone through electrical signals known as nerve impulses. Impulses
are positively charged waves that flow along the axon to the synaptic knob. There is a narrow gap
called synapse that separates the synaptic knob from neurone dendrites that receive the impulses.
Electrical signals that carry information must be transferred across synapses for impulses to be
transmitted to the following neurone.

Motor neurone

dendrite

direction of impulse flow

cell body

nucleus
axon synaptic

knob  Sensory neurone

direction of impulse flow

dendrite

cell body
nucleus

synaptic knob

Relay neurone

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12.3.4

Synapses play an important role in allowing nerve impulses to travel
in one direction. Therefore, synapses control the types of impulses that
pass through them.

Transmission of impulse across a synapse
Impulses are transmitted chemically across synapses. The chemical
substances involved are neurotransmitters that are kept in synaptic
vesicles that are found at the end of the synaptic knob. Two examples
of neurotransmitters found in most synapses are acetylcholine and
noradrenaline. Other examples are serotonin and dopamine.
The process of transmitting impulses through synapses is slow as it
occurs chemically. At first, the electrical signal will be changed to a
chemical signal in the form of a neurotransmitter, then the chemical
substance is converted again to an electrical signal on the membrane of
the receiving neurone. The transmission of impulses across synapses is
shown in Figure 12.9.

The cobra’s poison
can cause paralysis by
preventing the action
of the neurotransmitter.

Biological Lens

ICT 12.1

Video: Synapse
(Accessed on 21 August 2019)

FIGURE 12.9 Transmission of impulses across synapses

1 When electrical impulses reach
the synaptic knob, synaptic
vesicles are stimulated to release
neurotransmitters into the synapse.

Synaptic knobs contain numerous mitochondria to generate the energy required for the transmission
of nerve impulses.

1

2
3

synapse

neurotransmitter

mitochondrion

synaptic knob

synaptic
vesicle

receptor
protein

receiving
neurone

2 The neurotransmitters
diffuse through the
synapse and combine
to a specific receptor
protein which is a
receptor on the dendrite
of the receiving neurone.

3 The binding of the
neurotransmitter and
the receptor stimulates
the initiation of the next
impulse so that impulse
can be transmitted
through the neurone.

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12.4  Voluntary and Involuntary
Actions
Responses produced are either voluntary action or involuntary
action. What are the pathways of information transmission involved in
both actions? What are the differences between voluntary action and
involuntary action? Table 12.2 shows the comparison between voluntary
and involuntary actions.

12.4.1

TABLE 12.2 Comparison between voluntary action and involuntary action
Voluntary action Involuntary action

Similarity

Both actions involve stimulation, impulse, neurone and an effector organ.

Differences

Actions that we are conscious of and
done on our own will

Actions that occur automatically
and occurs without us being
conscious

Involves the somatic nervous system
Involves the autonomous nervous
system

Controlled by the cerebral cortex
Controlled by the medulla
oblongata and hypothalamus

Involves the reaction of the skeletal
muscles

Involves the reaction of the
smooth muscle and glands

Design a simulation
model of the nerve
coordination using an
electric circuit.

Activity Zone  1 What is the function of motor
neurones?

2 Why do synaptic knobs
contain a lot of mitochondria?

3 How are electrical impulses
transmitted through synapses?

4 Predict what would happen to
the transmission of impulses if
the neurone does not have a
myelin sheath.

12.3Formative Practice

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VOLUNTARY ACTIONS INVOLVING SKELETAL MUSCLES

• Voluntary actions such as walking, talking or brushing teeth are conscious actions.

• For example, you can voluntarily raise your hand to answer a question.

• The voluntary actions involving the skeletal muscles are controlled by the cerebral cortex.

• Since the information reaches the cerebral cortex, that is, our level of consciousness, our
perception of the surroundings can be produced.

• The information pathway in voluntary action is demonstrated in Figure 12.10.

12.4.2

Involuntary actions involving skeletal muscles:
reflex response
Three-neurone reflex arc
• Several situations require immediate and spontaneous action.
• If you accidentally prick your finger on a sharp pin, you will move your finger

immediately without much thought.
• This is known as a reflex action.
• A reflex action is a fast response a stimulus without being controlled by the brain.
• The nerve pathway involved in a reflex action is called the reflex arc

(Figure 12.11).
• The reflex action of moving the finger from the sharp pin involves three neurones

and communication between the neurones in the peripheral nervous system and
the spinal cord.

FIGURE 12.10 The pathway of information transmission in voluntary
actions that involve skeletal muscles

Stimulus occurs
when the teacher
questions pupils.

1

motor
neurone

sensory
neurone

The pupil’s receptor
receives the stimulus
and transmits the
nerve impulse to the
cerebrum through
the sensory neurone.

2

The cerebrum interprets
the nerve impulse to be
sent to the effector.

3

The effector (skeletal
muscles) receives the
information.

4
The pupil raises his
hand to answer the
question (response).

5

relay neurone

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Sensory receptor stimulated

pin

cell body of sensory neurone
dorsal root

spinal cord

ventral
rootspinal

nerve
motor neurone

sensory neurone

relay neurone

cell body of motor neurone

central canal

grey matter

white matter

effector

1

2

3

4

5

dorsal root ganglion

The importance of reflex actions
• Reflex actions produce spontaneous responses without waiting for

instructions from the brain.
• The additional  time that is needed by the brain to analyse

information before triggering a response can lead to serious injuries.
• Since reflex actions involve the spinal cord, the brain can focus on

higher-level thinking.

When a finger
is pricked by
a sharp pin,
the sensory
receptor
detects the
stimulus and
triggers a
nerve impulse.

In the spinal
cord, the
nerve impulse
is transferred
from the
sensory
neurone
through the
synapse to the
relay neurone.

From the relay
neurone, the
nerve impulse
is transferred
to the motor
neurone.

The motor
neurone
transfers the
nerve impulse
from the spinal
cord to the
effector (muscle
tissue) so that
the finger can be
moved quickly.

1 2 3 4 5

FIGURE 12.11 The reflex arc that involves three neurones and a spinal cord

The nerve
impulse is
transmitted
along the
sensory
neurone to
the spinal
cord.

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12.4.2 12.4.3

Two-neurone reflex arc
Another reflex action is the knee jerk or patellar reflex (Figure 12.12).
This reflex uses the nerve pathway that involves two neurones, that is,
the sensory neurone and the motor neurone. The doctor sometimes
tests the effectiveness of someone’s nerve system by tapping on the knee
using a rubber hammer (Photograph 12.3).

PHOTOGRAPH 12.3
Doctor testing knee jerk reflex

FIGURE 12.12 The reflex arc in knee jerk involving two neurones

spinal cord

white
matter

grey matter

dorsal root

sensory
neurone

dorsal root
ganglion

stretch
receptor

quadriceps
muscle

ventral
root

motor
neurone

biceps femoris
muscle

leg jerks
forward

tendon below
the kneecap

1

2

4

3

When the tendon below
the kneecap is knocked,
the quadriceps muscle
stretches and stimulates the
stretch receptors to trigger
nerve impulses.

1. The quadriceps muscle
contracts causing the leg to
jerk to the front.

1. The sensory neurone
transmits the nerve
impulses to the motor
neurone in the spinal cord.

1

4

2

Reflex actions such
as coughing protects
the lungs from foreign
particles from the
external environment.
The pupil reflex
protects the retina from
damage.

Our World of Biology

Draw a reflex arc.

Activity Zone

1. The motor neurone then
transmits impulses from
the spinal cord to the
quadriceps muscle.

3

1 State the sequence of impulse transmission
in the knee jerk reflex arc.

2 One example of reflex action is pulling the
hand away from a hot object. Define the
reflex action and state its importance.

3  Differentiate between voluntary and
involuntary actions.

4  Someone who loses a leg due to a certain
disease will still feel pain in the area where
the limb was amputated. Explain why.

12.4Formative Practice

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Health Issues Related to the
Human Nervous System
Nervous system disease
We should be thankful for having a central nervous system that
functions well. However, the central nervous system can become
damaged and stop functioning efficiently.
A few examples of health issues related to the nervous system are given
below.

12.5
The risk of
Alzheimer’s disease
is higher among
individuals who
rarely challenge
their minds to study
and think critically.

Our World of Biology

12.5.1

PARKINSON’S DISEASE

It is the shrinkage of the nervous system that causes tremors in the
limbs, jaw, foot and face. The patient will also have difficulty maintaining
body posture and balance.

ALZHEIMER’S DISEASE

This disease causes the loss of ability to reason and to take care of
oneself. The patient is usually confused, forgetful and disoriented even
in a familiar place. If the deterioration of the brain continues, the patient
will lose the ability to read, write, eat, walk and talk.

ATTENTION-DEFICIT HYPERACTIVITY DISORDER (ADHD)

A type of brain disease that causes someone to become hyperactive,
unable to concentrate and gets easily bored.

LOU GEHRIG/AMYOTROPHIC LATERAL SCLEROSIS (ALS)

This disease is caused by the deterioration and death of motor
neurones that control the movement of muscles such as chewing,
walking and talking.

AUTISM

A type of disease related to the development of nerves in the brain.
Autism causes an individual to experience problems communicating
and interacting.

MULTIPLE SCLEROSIS

A progressive disease as a result of an abnormality in the immune
system that attacks the myelin sheath in the brain and spinal cord. The
damaged myelin sheath prevents the transmission of impulses from and
to the brain. EPILEPSY

The occurrence of
abnormal activities
in certain parts of
the brain causing the
nerve cells to produce
unusual signals. A
person suffering from
epilepsy may become
unconscious and
experience muscle
spasms.

BRAIN PARALYSIS
(CEREBRAL PALSY)

Brain paralysis occurs
because of brain
damage before or after
a baby is born. It could
also possibly occur in
children between the
ages of 3–5 years old.
This disease causes
failure in muscles and
the ability of motor
neurones to function
properly.

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12.5.2

Activities2.1 Research
study

Traditional methods of treatment for health
issues related to the nervous system

Activity 12.1

Materials
Medical magazines, Internet

Procedure
Conduct a research study on the use of traditional methods (acupuncture, reflexology
and others) in the treatment of health issues related to the nervous system.

Discussion
What are the traditional methods that can treat health issues related to the nervous system?

The effects of drug and alcohol abuse on
human coordination and response

There are many types of drugs used for medical purposes, for example,
marijuana is used by doctors in small quantities to reduce nausea in cancer
patients after undergoing chemotherapy treatment. However, drug abuse
other than for medical purposes can cause serious side effects and
would most likely be fatal. Among the effects of drug abuse on
drug addicts are:
• addiction
• an addiction that causes withdrawal symptoms

such as shivering, sweating and vomiting if the
drug is not taken

Table 12.3 shows the effects of drug and alcohol on
human coordination and response.

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12.5.2

TABLE 12.3 Drugs and alcohol and their effects on the nervous system
Substance Effects

Stimulant drugs (stimulants) • Increases the activity of the central nervous system

• Excessive use causes temporary euphoria which is followed by
depression

Sedative drugs (depressants) • Delays the transmission of nerve impulses

• Calms the mind

Hallucinogenic drugs • Causes the user to hallucinate

• Relief from pain and anxiety

Narcotic drugs • Delays the normal functions of the brain

Alcohol • Disrupts coordination and thinking

• Delays the transfer of nerve impulses

1 State the symptoms of Alzheimer’s disease.

2 Explain how drugs affect the coordination of
one's nerves.

3 Why do doctors use drugs in the treatment of
cancer patients who undergo chemotherapy?

4 Explain why a drunk individual is not
allowed to drive a vehicle.

12.5Formative Practice

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Endocrine System
The coordination system of the body needs cooperation between
the endocrine system and the nervous system. Both systems play an
important role in maintaining homeostasis.  Even though both systems
have different functions, they interact and complement each other to
regulate and coordinate all processes and activities in the body. What is
the endocrine system?

Endocrine System of Humans
The endocrine system is made up of glands that secrete chemical
substances, that is hormones. The endocrine glands are ductless glands.
So, the hormones are secreted directly into the blood flow. Even though
the hormones are transported throughout the body in the blood, the
hormones only influence and affect specific target cells. The hormones
bind with specific molecule receptors on the membrane surface of target
cells and produce specific responses.
The endocrine system of humans is made up of many glands. The
glands secrete different hormones involved in specific physiological
processes. The functions of hormones can be divided into three main
functions: reproduction, growth and homeostasis. Figure 12.13 shows
the endocrine glands.

12.6

FIGURE 12.13 The endocrine glands in the endocrine system of humans

Millennial Career

Endocrinology is a
branch of medicine
that is related to
the diseases of the
endocrine system
and problems with
hormone secretion.

Millennial Career

12.6.1 12.6.2

hypothalamus

pituitary gland

thyroid gland

adrenal gland

pancreas

ovary

testis

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TABLE 12.4 The functions of hormones that are secreted by the posterior
lobe of the pituitary gland

The functions of hormones secreted by each endocrine
glands
The pituitary gland is the main gland of the endocrine system because it secretes hormones that
control the secretion of other endocrine glands. The pituitary gland is located at the bottom of the
hypothalamus in the brain. The pituitary gland is made up of two lobes, which  are the anterior lobe
and the posterior lobe. Each lobe secretes hormones that have certain functions (Table 12.4 and
Table 12.5).

12.6.3

TABLE 12.5 The functions of hormones that are secreted by the anterior lobe of the pituitary gland
Anterior Lobe of the Pituitary Gland

Hormone
Target Tissues/

Organs
Function

Luteinizing hormone
(LH)

• Ovary • Stimulates ovulation, development of corpus luteum,
and secretion of oestrogen and progesterone

• Testis • Stimulates secretion of testosterone

Growth hormone
(GH)

Soft tissue, bone Stimulates growth, protein synthesis and fat metabolism

Adrenocorticotropic
hormone (ACTH)

Adrenal cortex Stimulates the adrenal cortex to secrete hormones

Thyroid-stimulating
hormone (TSH)

Thyroid gland Stimulates thyroid to secrete thyroxine

Follicle-stimulating
hormone (FSH)

• Ovary • Stimulates the development of follicles in the ovary

• Testis • Stimulates spermatogenesis

Posterior Lobe of the Pituitary Gland

Hormone
Target Tissues/

Organs
Function

Antidiuretic
(ADH)

Kidney tubule
Stimulates the
reabsorption of water

Oxytocin

• Uterine muscles

• Mammary
glands

• Stimulates the
contraction of uterine
muscles during birth

• Stimulates the
production of milk from
the mammary gland

hypothalamus

anterior lobe

posterior lobe

The hormone that regulates the secretion of other hormones is known as the stimulating hormone.
This includes thyroid-stimulating hormone (TSH) and adrenocorticotropic hormone (ACTH). For
example, TSH stimulates the thyroid gland to secrete thyroxine.
Hormones that act directly on target organs include growth hormone, oxytocin and antidiuretic
hormone (ADH). For example, GH acts directly on the bone.
The hypothalamus secretes gonadotrophin-releasing hormone (GnRH). GnRH stimulates the
pituitary gland to secrete FSH and LH into the blood.

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12.6.3

FIGURE 12.14 The functions of hormones
secreted by other endocrine glands

TESTIS

Hormone: Testosterone

Target tissues/organs:
Gonad, skin, muscles and
bones

Function: Stimulates the
development of secondary
sexual characteristics in the
male and spermatogenesis

THYROID GLAND

OVARY

Hormone: Thyroxine

Target tissues/organs: All
tissues

Function:

• Increases the metabolism rate

• Increases body temperature

• Regulates growth and
development

PANCREAS

Hormone: Insulin

Target tissues/organs: Liver,
muscles and adipose tissues

Function: Reduces blood
glucose level and promotes the
conversion of excess glucose
to glycogen

Hormone: Glucagon

Target tissues/organs: Liver,
muscles and adipose tissues

Function:

• Increases the blood glucose
level

• Promotes the conversion of
glycogen to glucose

Hormone: Oestrogen

Target tissues/organs: Gonad, skin, muscles and bones

Function:

• Stimulates the development of secondary sexual
characteristics in the female and maturity of the follicles

• Repairs and stimulates the thickening of the uterus wall

Hormone: Progesterone

Target tissues/organs: Gonad

Function: Stimulates the development of the uterus wall and
the formation of the placenta

MALE FEMALE

ADRENAL GLAND

Hormone: Aldosterone

Target tissues/organs:
Kidney

Function: Increases the
reabsorption of salt in kidneys

Hormone: Adrenaline

Target tissues/organs:
Muscle tissues, liver and heart

Function:

• Increases the level of
sugar and fatty acids in
the blood

• Increases the respiratory
rate and heartbeat

• Increases the rate of
metabolism and contracts
blood vessels

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Involvement of the nervous system and endocrine system in
a ‘fight or flight’ situation
Have you ever been in a state of ‘fight or flight’ situation? For example, when a dog or a goose
suddenly  chases you? How do you feel in a situation like this? Your heart will beat fast and your
palms will sweat. What causes this condition?

12.6.4

In an emergency or a ‘fight or flight’ situation, the hypothalamus transmits nerve impulses directly
to the adrenal medulla and the adrenal medulla cells are stimulated to secrete adrenaline and
noradrenaline. These two hormones act quickly to produce the required responses in a ‘fight or
flight’ situation. This includes an increase in:
• heart rate
• respiratory rate
• blood pressure
• blood glucose level
• metabolic activity
The heart pumps more oxygen and glucose to the brain and skeletal muscles because additional
energy is needed to fight or run quickly. In an emergency, both the endocrine system and the nervous
system work together to produce an immediate response to deal with the dangerous situation. When
this mechanism manages to control this ‘fight or flight’ situation, bodily changes that have occurred
return to the normal range.
What are the similarities and differences between the endocrine system and the nervous system?
Figure 12.15 compares and contrasts the two systems.
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FIGURE 12.15 Similarities and differences between the nervous system and the endocrine system

12.6.5

Contains target tissues
or organs

Produces a response to
a stimulus

Functions to regulate
all activities of the body

It is made up of a
network of millions
of neurones

The duration
of the effect is
short

Signal is in the
form of electrical
impulses through
neurones

Nerve response
is quick and
immediate

The effect of an
impulse produces
the response of
an organ

Consists of
ductless endocrine
glands

The duration of
the effect is long

Signal is delivered
by organic chemical
substances, which
are hormones,
through blood flow

The effect of
hormones
produces
responses in
several organs

NERVOUS
SYSTEM

ENDOCRINE
SYSTEM

The endocrine system plays a key role in maintaining the homeostasis of the body. However, an
imbalance in hormone production can occur in some individuals when the endocrine gland secretes
excessive or insufficient hormone. What is the effect of hormone imbalance to the individual?

1  Name the hormone that is related to the
function given.

2 State three characteristics of hormones.

3 Compare between the nervous system and
the endocrine system.

4 A pupil finds herself being followed by a van
and suspects there is an attempt to kidnap
her. In a state of panic, the pupil is able to
run fast and far away from the van. Explain
the ‘fight or flight’ in this situation.

12.6Formative Practice

Hormone Function

Stimulates the contraction of
uterine muscles during birth

Stimulates water absorption
by the kidneys

Increases the metabolism rate
of most of the body cells

The response
is slow and
prolonged

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Health Issues Related to the
Human Endocrine System12.7

A diabetes mellitus patient does not produce enough
insulin or cannot use the insulin produced. As a result,
the level of glucose in the blood is high. The patient
urinates frequently, is always thirsty, experiences
numbness in the soles of the feet, has  blurred vision, is
tired and their wounds heal much slower. Whereas, the
excessive secretion of insulin causes hypoglycaemia
where the blood glucose level is too low. Among the
symptoms of hypoglycaemia are fatigue, difficulties
sleeping at night, disordered thoughts, fear, emotional
instability, faints easily and headache.

DIABETES MELLITUS

For diabetes insipidus patients,
the posterior lobe of the pituitary
gland fails to secrete the
antidiuretic hormone (ADH). As
a result, patients will produce a
large amount of urine and often
feel thirsty. Since a large amount
of water is lost through the urine,
the individual will experience
dehydration if they do not drink
enough water every day.

DIABETES INSIPIDUS

An adult will experience hypothyroidism
if there is inadequate thyroxine secretion.
Symptoms include extremely slow
heartbeat, extremely sensitive to cold,

tiredness and gain weight easily.

HYPOTHYROIDISM

dry, rough and
sparse hair

thin eyebrows

bloated,
dry skin

oedema

Hyperthyroidism refers to a situation that occurs when too
much thyroxine is secreted. Symptoms include excessive
sweating, heat intolerance, increased frequency of defaecation,
fear, heart palpitations and weight loss. Sometimes, the thyroid
gland will grow two or three times larger than its original size
(Photograph 12.5).

HYPERTHYROIDISM

PHOTOGRAPH 12.5 Enlarged thyroid
gland

12.7.1

PHOTOGRAPH 12.4 An individual who has
hypothyroidism

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12.7.1

PHOTOGRAPH 12.6 The hands of a 12-year-old
boy with gigantism. Observe that his hands are
bigger than that of a normal adult

PHOTOGRAPH 12.7 Chandra Bahadur Dangi from Nepal
(0.55 m), the shortest man in the world and Sultan Kosen
(2.47 m), the tallest man in the world

hands of a child with
gigantism

hands of a normal
adult

Low secretion of the growth hormone (GH)
during the period of growth delays the
growth of bones and causes a condition
called dwarfism (Photograph 12.7). Organs
also fail to develop and parts of the body
ratio remain as that of a child.

DWARFISM

1 State the factors that cause a person to
contract diabetes insipidus.

2 State two symptoms experienced by people
with diabetes mellitus.

3 Goitre is a disease that causes the
enlargement of the thyroid gland. In your
opinion, why are goitre patients encouraged
to eat seafood?

4 Suggest a treatment for children with
stunted growth due to growth hormone
deficiency.

12.7Formative Practice

Excessive secretion of the growth hormone
(GH) during childhood causes gigantism
which is a condition characterised by the
abnormal elongation of bones (Photograph
12.6). The individual grows to become
extremely tall.

GIGANTISM

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COORDINATION AND RESPONSE IN HUMANS

• Stimulus
• Receptor
• Integration

centre
• Effector
• Response

Central nervous
system
Interpreting
information and
sending a response
to an effector
through the motor
neurones
• Brain
• Spinal cord

Peripheral nervous system
Linking the sensory receptor and
effector with the central nervous
system
• Sensory receptor
 – Chemoreceptor: Detects chemical

substances
   – Mechanoreceptor: Detects

touch and pressure stimulation
  – Photoreceptor: Detects light
  – Thermoreceptor: Detects change

in temperature
   – Baroreceptor: Detects change in

pressure
   – Nociceptor: Detects pain
• Somatic nervous system
 Controlling voluntary actions
• Autonomous nervous system
 Controlling involuntary actions

Coordination
and Response

Nervous
System

• Sensory neurones
• Relay neurones
• Motor neurones

• Endocrine gland
• Hormone
• Involvement of

the nervous
and endocrine
system in a “fight
or flight” situation

• Compare and
contrast the
nervous and the
endocrine system

• Dwarfism
• Gigantism
• Hyperthyroidism
• Hypothyroidism
• Diabetes mellitus
• Diabetes insipidus

Voluntary action
Actions that we are
conscious of and
done on our own
will

Involuntary action
Action that occurs
automatically
and involves an
autonomous
nervous system
and controlled
by the medulla
oblongata

• Multiple sclerosis
• Alzheimer's disease
• Parkinson's

disease
• Lou Gehrig/

Amyotrophic
Lateral Sclerosis
(ALS)

• Attention Deficit
Hyperactivity
Disorder (ADHD)

• Autism
• Brain paralysis

(Cerebral palsy)
• Epilepsy

Neurones and
Synapse

Type of Action

Endocrine System

Health Issues Related to
the Human Nervous System

Health Issues
Related to the

Human Endocrine
System

Summary

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Have you mastered the following important concepts?
• Sequence of components in the coordination of humans
• Structure of the human nervous system
• Functions of the brain
• Function of a neurone in the transmission of impulse
• Structure and functions of synapses
• Transmission of a nerve impulse across a synapse
• Voluntary and involuntary actions
• Reflex arc involving two neurones and three neurones
• Health issues related to the nervous system
• Effects of drug and alcohol abuse on coordination
• Functions of hormones secreted by endocrine glands
• Compare and contrast the nervous and the endocrine system
• The effects of hormonal imbalance on human health

1 Compare the functions of the cerebellum and the medulla oblongata.

2 Define reflex action and state its importance.

3 Name the main endocrine gland in the endocrine system of humans. Why is this gland
considered the main gland?

4 State the effects of excessive and insufficient growth hormones (GH) in humans.

Self Reflection

Summative Practice 12

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5 Figure 1 shows the cross section of a part of the nervous system.

(a) (i) Name structure X.

(ii) State the function of structure X.

(b) Why is part Y swollen?

(c) Complete Figure 1 with neurones
involved in a reflex action. Mark the
direction of impulse on the neurone.

(d) If the spinal nerve is cut at Z, what is the
effect on the organ that is connected to
it? Explain why.

6 Figure 2(a) shows part of a motor neurone and Figure 2(b) shows a cross section of a
synaptic knob.

FIGURE 2
  (a) Name the parts labelled V, T and U.

(b) Name the chemical substances in U.

(c) The synaptic knob contains a lot of V. What is the function of V?

(d) Draw an arrow that shows the direction of impulse flow along axon S.

(e) Explain

(i) why does the transmission of impulse involve the pathway of impulse through T.

(ii) how transmission of impulse occurs.

(f) Based on Figures 2(a) and (b), explain why transmission of impulse through a neurone
occurs in one direction only.

FIGURE 1

Z

X
Y

Impulse direction from
nearby neurones

axon S

T

U

V

(a)                       (b)

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Essay Questions

7 Explain the effects of stimulant drugs and sedative drugs on the transmission of impulse
through the synapse.

8 (a) (i) Compare and contrast the nervous system and the endocrine system.

(ii) Nora accidentally stepped on a nail. She screamed while holding on to her injured
foot. Describe Nora’s reaction when she stepped on the nail.

(b) After tea time, Azman went to the playground to ride his bicycle. While riding his
bicycle, Azman is conscious of his action. However, he is not conscious of what is
happening to the food that he had just eaten. Describe why Azman is conscious of his
action riding the bicycle but is not conscious of the food he had just eaten.

Enrichment

9 How does the brain decide in determining how much energy is needed to lift a piece of
paper compared to a book?

10 Explain why we have to understand and display a lot of patience when taking care of an
Alzheimer’s or Parkinson’s patient.

Complete answers are
available by scanning the
QR code provided

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13
CHAPTER

Homeostasis
and the Human
Urinary System

•	 What	does	homeostasis	mean?	•	 How	are	your	body	temperature,		blood	sugar	level,	the	partial	pressure	of	carbon	dioxide	and	blood	pressure	regulated?
•	 What	is	the	structure	and	function	of		the	kidney?
•	 How	is	urine	formed?
•	 How	does	the	negative	feedback	mechanism	in	homeostasis	happen?•	 What	are	the	health	issues	related	to	the	urinary	system?

Do you KNOW…

How can
diabetes cause
kidney failure?

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13.1 Homeostasis

13.1.1  Explain the meaning of homeostasis.
13.1.2  Justify the necessity to maintain

physical and chemical factors in
the internal environment.

13.1.3 Describe the involvement of various
organ systems in maintaining an
optimal internal environment.

13.1.4 Apply the knowledge of
homeostasis concept in
regulation of:

• body temperature
  • blood sugar levels
  •  the partial pressure of carbon

dioxide
  • blood pressure

13.2 Urinary System

13.2.1 Identify the structure and functions
of a kidney.

13.2.2 Draw, label and explain the
structure of a nephron and
collecting duct.

13.2.3 Describe the formation of urine:
  • ultrafiltration
  • reabsorption
  • secretion
13.2.4 Synthesise the concept of

homeostasis by using negative
feedback mechanism in
osmoregulation.

13.2.5 Conduct an experiment to study
the effects of different volumes of
water intake on urine formation.

13.3  Health Issues Related to the Urinary
System

13.3.1 Describe health issues that are
related to the urinary system.

Glomeruli
and renal
tubules

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Homeostasis
Homeostasis
Homeostasis is the regulation of physical and chemical factors of the
internal environment within normal ranges for the cell to function in
optimum conditions.

Physical and chemical factors of the internal
environment

The physical factors that need to be regulated are temperature,
osmotic blood pressure and blood pressure. The

chemicals that need to be regulated are pH value,
the concentration of minerals and blood sugar

concentrations.
Any deviation from the normal range triggers
the homeostatic mechanism which involves
negative feedback. Homeostasis regulates the
internal environment in order for it to be in a
constant state although the external environment
changes a lot. This ensures that cell activity
continues to function at the optimum level.

Figure 13.1 shows the negative feedback mechanism
of homeostasis.
In homeostasis,
(a)  a factor that exceeds the normal range is

brought down to the normal range
(b)  a factor that falls below the normal range is

increased to the normal range

The organ system involved in maintaining an optimal
internal environment
In the body, various organ systems function and interact with each other
to maintain an optimum internal environment.

13.1

13.1.313.1.213.1.1

FIGURE 13.1 Deviation from the normal range triggers
the mechanism of homeostasis to return a factor’s value
to the normal range

Value decreases
Value in

cre
as

es

Homeostatic
mechanism

Regulatory
system

Regulatory
system

Normal
range

Normal
range

V
al

ue
 in

cre
ases         Value decreases

•	 Body temperature is regulated by the integumentary system
(skin and sweat glands), nervous system, circulatory system,
muscle system and endocrine system.

•	 Blood	 sugar	 levels are regulated by the endocrine gland,
circulatory system and digestive system.

•	 The	partial pressure of carbon dioxide in the blood is regulated
by the respiratory system, circulatory system and nervous system.

•	 Blood pressure is regulated by the circulatory system and nervous
system.

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Regulating body temperature
Maintaining the body temperature at a fixed range is important so that cell metabolism reactions
that are catalysed by enzymes occur at optimum levels. Temperatures that are too high will denature
enzymes, while temperatures that are too low will slow down the metabolic activity of the cell, and
prevent it from carrying out cell processes.
These changes in body temperature are detected by the thermoreceptors in the skin and the
hypothalamus. Figure 13.2 shows the regulation of body temperature by different effectors when
the body temperature increases beyond normal ranges. Figure 13.3 shows the regulation of body
temperature by different effectors when the body temperature decreases below normal ranges.

13.1.4

The adrenal glands are
less stimulated to secrete
adrenaline. Metabolic rate
decreases.

Arterioles in
the skin dilate
(vasodilation)
to allow more
blood to flow to
the skin surface.
More heat is lost
to the external
environment
through radiation.

Erector muscles
are less stimulated
so they do not
constrict and the
fine hair will lower
towards the skin
surface. As a result,
a thin layer of air is
trapped between
the fine hair. Heat
can be released
quickly.

The sweat glands are
stimulated to produce more
sweat. Heat is absorbed to
evaporate sweat, and this cools
the skin.

Skeletal muscles
contract and relax
less. The body
does not shiver.

erector
muscles relax

fine hair
lowers
towards the
skin surface

adrenal gland

kidney

The thyroid gland is not
stimulated and the secretion
of thyroxine is reduced.
Metabolic rate decreases.
No excess heat is generated.

Thermoreceptors in the hypothalamus

Thermoreceptors in the skin

detected by

Body
temperature
rises above
normal
ranges

epidermis
(skin)

heat loss through the epidermis

arteriole
dilates

Regulation of Body Temperature by Effectors through Physical Methods

Regulation of Body Temperature by Effectors through Chemical Methods

skeletal muscles

FIGURE 13.2 Body temperature regulation when temperature increases

hypothalamus
(temperature
control centre)

pituitary gland

thyroid
gland

larynx

trachea

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Skeletal muscles will contract and
relax so the body will shiver. This
generates heat which in turn raises
the body temperature because the
constriction of muscles requires
energy.

FIGURE 13.3 Body temperature regulation when temperature decreases

Arterioles in the
skin are stimulated
to constrict
(vasoconstriction).
The result is less blood
flow to the surface of
the skin. With that,
less heat is lost to the
external environment
through radiation.

Erector muscles are
stimulated so they
contract, causing fine
hair to stand erect. A
thick layer of air trapped
between the fine hairs
acts as an insulator that
prevents loss of heat
from the skin.

The sweat gland
is not stimulated.
Sweating does
not happen.

skeletal muscles

The adrenal glands are
stimulated to secrete more
adrenaline. This hormone
speeds up the conversion
of glycogen to glucose.
Metabolic rate increases.
The oxidation of glucose
releases heat to warm
the body.

The thyroid gland is
stimulated to secrete
more thyroxine which will
increase the metabolic
rate. More heat is
generated for the body.

13.1.4

Thermoreceptors in the hypothalamus

Thermoreceptors in the skin

detected by
Body
temperature
drops below
normal ranges

Regulation of Body Temperature by Effectors through Physical Methods

Regulation of Body Temperature by Effectors through Chemical Methods

erector
muscles
contract

fine hairs
raised

adrenal gland

kidney

kelenjar
peluh

liang
peluh

sweat
gland

sweat
pore

hypothalamus
(temperature
control centre)

pituitary gland

epidermis (skin)

arteriole
constricts

thyroid
gland

larynx

trachea

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Regulation of blood sugar levels
The pancreas is responsible for maintaining blood sugar (glucose)
levels within the normal range of 75–110 mg/100 ml. Langerhans cells
in the pancreas produce and secrete insulin and glucose continuously
into the bloodstream to regulate blood sugar levels. The actions of both
these hormones and the mechanism of homeostasis work together to
maintain the blood sugar levels within the normal range as described
in Figure 13.4.

FIGURE 13.4 Regulation of blood sugar levels

Failure in the production, secretion and intake of insulin by target
cells can cause diabetes mellitus. The blood sugar level of diabetic
patients is usually high and unstable after a meal. The patient also feels
thirsty, tired, fatigued and suffers weight loss. Diabetes mellitus can be
controlled through insulin injections, pills that lower blood sugar levels
and a proper diet.

Scientific studies
have confirmed that
cinnamon can lower
blood sugar levels.

Malaysian Innovation

13.1.4

ICT 13.1

Video: Regulating blood sugar
levels in normal individuals

and diabetic patients
(Accessed August 21 2019)

•	 Insulin stimulates the
muscle cells to use
glucose in the process of
cell respiration.

•	 Insulin stimulates the
conversion of excess
glucose into glycogen to
be stored in the liver and
muscle cells.

•	 In adipose cells, insulin
converts excess glucose
to fat.

•	 Glucagon stimulates liver
cells to convert glycogen to
glucose.

•	 Glucagon also promotes
the breakdown of fat to
release fatty acids that can
be metabolised to produce
energy.

Alpha cells (α) in pancreatic
Langerhans cells are stimulated to
secrete glucagon into the blood.

Beta (β) cells in pancreatic Langerhans
cells are stimulated to secrete insulin
into the blood.

Blood sugar levels drop (in between meals)

pancreas

negative
feedback

adipose cells

liver

Blood sugar levels
go back to normal

Blood sugar levels increase (after a meal)

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During vigorous
activity, the
partial pressure
of carbon
dioxide increases
because of cellular
respiration.

pH values of blood and tissue
fluid that flood the brain
(cerebrospinal fluid) decreases.

This change in pH is
detected by the central
chemoreceptor in the
medulla oblongata
(sensory cells that are
sensitive to chemicals)
and peripheral
chemoreceptor in the
neck (carotid body
and aortic body)
(Figure 13.6).

Respiration
control centre and
cardiovascular
control centre
inside the medulla
oblongata.

Intercostal muscles,
diaphragm and
cardiac muscles
contract and relax
quickly.

Breathing rate, heart
rate and ventilation
rate increase. This
causes more carbon
dioxide gas to be
expelled from the
lungs.

Partial pressure of
carbon dioxide and
blood pH levels go
back to normal.

Nerve impulses
triggered and
sent

nerve impulse
sent

FIGURE 13.5 Process of regulating partial pressure of carbon dioxide in the blood

Noni fruit (Morinda
citrifolia) is believed
to be able to lower
high blood pressure.
Juice extracted from
this fruit has been
marketed on a large
scale.

Our World of Biology

13.1.4

Regulation of partial pressure of carbon dioxide
in the blood
Breathing is an involuntary action that is regulated by the respiratory
control centre in the medulla oblongata. The respiratory control centre
helps maintain homeostasis by controlling the partial pressure of carbon
dioxide in the blood (Figure 13.5).

cerebrum

medulla
oblongata

intercostal muscles

diaphragm

Carbon dioxide dissolves in blood plasma to
form carbonic acid. Carbonic acid is broken
down into hydrogen ions and bicarbonate ions.

Carbon
dioxide

Water Carbonic
acid

Hydrogen
ion

Bicarbonate
ion+                             +

FIGURE 13.6 Aortic body, carotid body and
baroreceptor

carotid
artery

aortic body

carotid body

baroreceptors
in the carotid
artery

baroreceptor in
the aortic arch

heart

aortic
arch

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Blood pressure returns
to the normal ranges.

blood pressure increases
blood pressure
drops

When an individual’s
blood pressure drops, for
example, if there is serious
bleeding.

The cardiovascular control
centre in the medulla
oblongata is less stimulated.

•	 Arterial vasoconstriction
occurs. This adds resistance
to the flow of blood in the
bloodstream.

•	 Stronger contractions of cardiac
muscles occur.

•	 Vasodilation occurs. This
reduces the resistance of
the flow of blood in the
bloodstream.

•	 Weak contractions of cardiac
muscles occur.

Blood pressure returns
to the normal ranges.

Blood pressure regulation mechanism
Baroreceptors or pressure receptors are located in the aortic arch and
carotid artery (Figure 13.6). The carotid artery is the artery in the
neck that supplies blood to the head. These receptors detect the pressure
of blood flowing through them and continuously send impulses to
the cardiovascular control centre in the medulla oblongata to regulate
blood pressure (Figure 13.7).

Vasoconstriction

Vasodilation

FIGURE 13.7 Blood pressure regulation

13.1.4

When an individual’s blood
pressure increases, for example
during vigorous activities.

Baroreceptors in the aortic arch
and carotid artery are stimulated.

The cardiovascular control centre
in the medulla oblongata is
stimulated.

Baroreceptors in the aortic
arch and carotid artery are
less stimulated.

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Urinary System
The human urinary system plays an important role in homeostasis.
The urinary system is made up of the kidneys, ureters, bladder and
urethra (Figure 13.8). The function of the urinary system is to excrete
nitrogenous compound wastes such as urea, as well as regulate the
volume of body fluids, blood osmotic pressure, ion concentration in
body fluids, electrolyte content and blood pH.

Structure and function of the kidneys
The kidneys consist of the cortex and medulla. Urine that is formed in
the kidneys flows into the pelvis.
The kidneys have two main functions:
 (a) excretion
 (b) osmoregulation
As an excretory organ, the kidneys excrete toxic wastes (nitrogenous
compounds) such as urea, uric acid, ammonia and creatinine.
As an osmoregulatory organ, the kidneys control:
•	 the total volume of water in body fluids
•	 the concentration of ions in body fluids
•	 blood osmotic pressure, which is the concentration of dissolved

materials and volume of blood and body fluids
•	 electrolyte content and pH of blood and body fluids

13.2

Do you know that the
right kidney is located
lower than the left
kidney? This difference
in position is because
the liver takes up a lot
of space above the
right kidney.

Biological Lens

13.2.1

1 What is the meaning of homeostasis? Explain how homeostasis
happens.

2 An employee had to work in hot conditions because the power
supply in his office got cut off. Describe the response of the
effectors in regulating his body temperature.

3 A 40-year-old man was diagnosed by a doctor as unable
to produce enough insulin. Describe what has happened to
the man.

4 Ahmad has just finished a 100 m sprint run. Explain how his blood
pressure is lowered back to normal range.

13.1Formative Practice

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kidney

renal vein
renal artery

ureter

bladder

urethra

FIGURE 13.8 Urinary system and cross section of the kidney

13.2.1

cortex

medulla

pelvis

The renal artery carries
oxygenated blood from the
heart to the kidneys.

The renal vein carries
deoxygenated blood from
the kidneys back to the heart.

Urine flows to the bladder
through the ureter.

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blood flow

flow of filtrate
passive transport

active transport

osmosis

H2O

glucose, amino acids

urea

Indicator:

•	 Each kidney is made up of millions of functional units called nephrons (Figure 13.9).

•	 Each nephron is made up of the following structures:
	 •	Bowman’s	capsule	 	 	 	 •	Glomerulus	 	 	 	 •	Renal	tubule

•	 Bowman’s capsule is cup-shaped and contains a cluster of blood capillaries called glomerulus.
The glomerulus is formed from the afferent arteriole branching from the renal artery. The glomerulus
merge again to form the efferent arteriole.

•	 The renal tubules are composed of the proximal convoluted tubules, loop of Henle and distal
convoluted tubule.

•	 The loop of Henle is a long U-shaped tubule that extends to the renal medulla. The distal
convoluted tubule of several nephrons join together into a collecting duct.

•	 The produced urine will flow from the collecting duct into the ureter.

NEPHRON

FIGURE 13.9 Structure of the nephron and urine formation

13.2.313.2.2

Formation of urine
There are three major processes involved in the production of urine, which are ultrafiltration,
reabsorption and secretion.

Cl–
Na+

K+

Cl–
Cl–

Na+
Na+

H+

NaCl
osmosis
pengangkutan aktif
pengangkutan pasif
aliran hasil turasan
aliran darah

H
2
O

glukosa, said amino
urea

Petunjuk:

blood flow

renal vein

afferent arteriole

glomerulus

efferent arteriole

renal artery

cortex

medulla

proximal
convoluted tubule

filtrate from
glomerulus

Bowman’s
capsule

loop of Henle

blood capillary
network

urine to
ureter

collecting
duct

processed filtrate
from other nephrons

distal convoluted tubule

renal fluid

1

2 4

3

5

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13.2.2 13.2.3

•	 In the loop of Henle, water is reabsorbed through osmosis. Sodium ions are reabsorbed through
active transport.

•	 In distal convoluted tubules, more water, sodium and chloride ions are reabsorbed.

•	 The amount of water and salts reabsorbed depends on the water and salt content in the blood.

REABSORPTION AT THE LOOP OF HENLE AND DISTAL CONVOLUTED TUBULES3

•	 Secretion is the process of secreting
waste materials in the blood that were not
filtered earlier into the renal tubules.

•	 This process is opposite to the process of
reabsorption.

•	 Secretion occurs along the renal tubule and
collecting duct, but is most active at the
distal convoluted tubule.

•	 Secretion occurs through simple diffusion
and active transport.

•	 Substances that are secreted include
hydrogen ions (H+), potassium ions (K+),
ammonium ions (NH4

+), urea, creatinine,
toxic substances and some drugs.

•	 Secretion gets rid of toxic wastes and helps
to regulate the levels of ions in the blood.

SECRETION4
•	 When the renal fluid reaches the collecting

duct, only a small amount of salts are left,
and most of the water has been absorbed
back into the bloodstream.

•	 The remaining renal fluid is now called
urine, flows down the collecting duct.
Here, a small amount of urea diffuses
out into the surrounding fluid and blood
capillaries due to its small molecular size.

•	 Urine contains water, urea, NaCl salt, uric
acid and creatinine.

•	 After leaving the collecting duct, urine flows
through the ureter, bladder, urethra and is
finally excreted.

URINE FORMATION5

•	 Blood entering the glomerulus is under high hydrostatic pressure because the diameter of
the afferent arteriole is larger than the diameter of the efferent arteriole. This pressure causes
ultrafiltration to occur, that is, fluid seeps through the walls of the glomerulus capillaries into the
cavity of Bowman’s capsule.

•	 The fluid that enters Bowman’s capsule is known as the glomerular filtrate.

•	 The glomerular filtrate has the same composition as blood plasma but does not contain red blood
cells, platelets and plasma proteins.

•	 Red blood cells and plasma proteins remain in the blood flowing to the efferent arteriole because
the size of these substances is too large to seep out of the glomerulus.

•	 Reabsorption of the glomerular filtrate occurs along the renal tubule. The dissolved substances
permeate across the renal tubular walls into the blood capillary network.

•	 In the proximal convoluted tubule, sodium ions (Na+) are actively pumped into the blood capillary
network and chloride ions (Cl–) are passively absorbed.

•	 The reabsorption of 100% glucose and amino acids also occurs through active transport.

•	 The movement of dissolved substances into the blood capillary network reduces the concentration
of dissolved substances in the glomerular filtrate but increases the concentration of dissolved
substances in the blood capillaries. As a result, water enters the blood capillaries through osmosis.

REABSORPTION AT THE PROXIMAL CONVOLUTED TUBULES2

ULTRAFILTRATION IN BOWMAN’S CAPSULE1

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13.2.4

Mechanism of homeostasis and osmoregulation
The body’s water content constantly changes depending on the intake of food and drinks.
Osmoregulation is the process of regulating water and salts in the body so that the blood osmotic
pressure can be maintained at a normal range. Osmoregulation is achieved by regulating the
volume of urine produced by the kidney. Figure 13.10 illustrates the osmoregulation of blood
osmotic pressure.

Osmoreceptors in the hypothalamus are
less stimulated.

Low ADH concentrations cause the walls of
the distal convoluted tubule and collecting
duct to become less permeable to water.

Less water is reabsorbed from the renal fluid
into the blood capillary.

Less concentrated urine is generated in high
volumes.

4

5

6

The pituitary gland is less stimulated.
So, less ADH is secreted from the
pituitary gland.

3

2

Blood osmotic pressure drops to below
normal range.

1 Blood osmotic pressure increases above
the normal range.

1

FIGURE 13.10 Osmoregulation of blood osmotic pressure

The pituitary gland is stimulated. So, more
ADH is secreted from the pituitary gland.

High ADH concentrations cause the
walls of the distal convoluted tubule and
the collecting duct to become more
permeable to water.

More water is absorbed from the renal fluid
into the blood capillary.

Urine that is very concentrated and low in
volume is generated.

4

5

6

3

Osmoreceptors in the hypothalamus are
stimulated.

2

NORMAL BLOOD OSMOTIC PRESSURE

Drinking too much water. Drinking too little water or loss of water due
to vigorous activity.

7 Blood osmotic pressure
returns to normal.

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13.2.5

Carry out the following activity to better understand how consuming different volumes of water can
affect urine production.

Problem statement
What is the effect of consuming different volumes of water on the volume of urine produced?

Hypothesis
The higher the volume of water consumed, the higher the volume of urine produced.

Variables:
Manipulated: Volume of water consumed
Responding: Volume of urine collected
Constant: Type of drink, age of pupil and time interval of urine collection

Specimen
Form 4 pupils

Materials
Boiled water that has been cooled

Apparatus
Cup, beaker to collect urine, stopwatch and measuring cylinder

Procedure
 1 Pupils should not eat or drink after 12 midnight the night before the experiment.

2 Pupils are divided into four groups according to their average weight.

3 Pupils are required to urinate before starting the experiment.

4 Each pupil is required to drink the following volumes of water:

(a) Group 1: drink 250 ml of water  (b) Group 2: drink 500 ml of water

(c) Group 3: drink 750 ml of water  (d) Group 4: drink 1000 ml of water

5 During the experiment, pupils should be at rest and are not allowed to carry out vigorous
activities.

6 Collect and measure the urine for each pupil after 20 minutes, 40 minutes and 60 minutes.

7 As soon as the urine is measured, it must be discarded into the toilet.

8 Record the average volume of urine collected for each group, for each time interval in the
following table.

9 Calculate the total volume of urine produced per group.

Results

Group
Volume of water
consumed (ml)

Average volume of urine collected
(ml)

Total volume of urine
produced  (ml)

20 minutes 40 minutes 60 minutes

1 250

2 500

3 750

4 1000

When identifying pupils for
this study, choose pupils
who are of approximately the
same weight.

Take Note!

Aktiviti2.1 To study the effects of consuming different
volumes of water on urine production

Activity 13.1 Experiment

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13.2.5

Discussion
 1 What is the relationship between the volume of water consumed and the production of urine?

Explain your answer.

2 How does the volume of urine change over time?

3 Explain how the volume of urine collected varies between an individual who drank 100 ml of
distilled water, and an individual who drank 100 ml of 5% sodium chloride solution.

Conclusion
Is the hypothesis accepted? State a suitable conclusion.

13.2Formative Practice

1 In which part of the kidney can the
proximal convoluted tubule, loop of Henle
and distal convoluted tubule be found?

2 Suggest two possible activities that can
cause the walls of the collecting duct to
become more permeable to water.

3 State how Na+ ions, water and glucose are
reabsorbed into the proximal convoluted
tubule.

4 An individual suffers damage in one kidney.
Does the individual need to undergo
haemodialysis? Suggest steps that this
individual needs to take in order to go
through his daily life without problems.

Materials
Internet, reference materials

Procedure
 1 In groups of four, gather information about haemodialysis.

2 Discuss the following.
  (a) Study the reasons of renal failure that cause a person to undergo haemodialysis.
  (b) Explain how haemodialysis works.

3 Make a report on your findings and present it to the class.

4 You can also carry out an activity to raise funds for haemodialysis centres through awareness
campaigns about the importance of helping patients in need of treatment.

Discussion
 1 Why would someone need haemodialysis?

2 How does haemodialysis work?

3 What is the effect on patients who do not receive treatment?

Aktiviti2.1 Gather information on and discuss
haemodialysis

Activity 13.2 Collecting
information

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kidney stone

13.3

13.3.1

ICT 13.2

Activity: Gather information and
discuss health issues related to

the urinary system

FIGURE 13.11 Formation of kidney stones in the kidney

Kidney stones can block the ureter
and reduce the production of urine.
To reduce the likelihood of kidney
stone formation, you should drink a
lot of water every day. Why?

Health Issues Related to the
Urinary System
Kidney failure can be caused by illness, bacterial infections or accidents.
Diabetes mellitus is the leading cause of renal failure, followed by
high blood pressure. Both these conditions damage the glomerulus.
Other than that, some individuals may face the problem of kidney
stone formation. Kidney stones are hard masses made of uric acid,
calcium oxalate or crystalline calcium phosphate.

1 Azman suffers from the formation of kidney
stones. Explain the effects of kidney stones
on his health.

2 Suggest two reasons why a person would
have kidney stones.

13.3Formative Practice

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HOMEOSTASIS AND THE HUMAN URINARY SYSTEM

Kidney stones

Homeostasis Urinary	System Health	Issues
Related	to	the
Urinary	System

Summary

Body temperature
Regulated	by	the	integumentary
system,	nervous	system,
circulatory	system,	muscular
system	and	endocrine	system

The partial pressure of
carbon dioxide in the blood
Regulated	by	the	respiration
system,	circulatory	system	and
nervous	system

Blood pressure
Regulated	by	the	circulatory	system
and	nervous	system

Blood sugar level
Regulated	by	the	endocrine
system,	circulatory	system	and
digestive	system

Regulation	of	physical	and
chemical	factors	of	the	internal
environment	within	normal
ranges	so	that	the	cell	functions
at	optimum	levels

Kidney:
•	Helps	regulate	water	and
salts	in	the	body

•	The	nephron	is	composed
of	the	Bowman’s	capsule,
glomerulus,	proximal
convoluted	tubule,	loop	of
Henle	and	distal	convoluted
tubule

The process of urine
formation
•	Ultrafiltration
•	Reabsorption
•	Secretion

Mechanism of homeostasis
and osmoregulation
•	Osmoregulation	of	blood
osmotic	pressure

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1 In which part of the kidney can the loop of Henle be found?

2 State the condition of urine that will be produced after an individual

(a) drinks plenty of water

(b) eats too much salty food

3 State a test that you can perform in the laboratory to determine whether a person has
diabetes.

4 Explain the role of the liver when blood sugar levels decrease.

5 Table 1 shows the concentration of amino acids in blood plasma and urine.

TABLE 1

Contents

Concentration in blood plasma that
enters the kidneys (g per 1000 ml)

Concentration in urine
(g per 1000 ml)

Amino acids 85 0

Have you mastered the following important concepts?
•	 The meaning of homeostasis
•	 The need to maintain the physical and chemical factors within the internal

environment
•	 The involvement of various organ systems in maintaining an optimum internal

environment
•	 The concept of homeostasis in regulation
•	 Structure and function of the kidneys
•	 Structure of the nephron and collecting duct
•	 The process of urine formation
•	 The concept of homeostasis and negative feedback in osmoregulation
•	 Health issues related to the urinary system

Self Reflection

Summative Practice 13

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(a) Explain the difference in the concentration of amino acids in blood plasma and urine.

(b) Both kidneys of a patient have failed. This condition causes water imbalance and an
accumulation of urea in the blood. State the effect of kidney failure on the regulation of
water balance in the blood.

6 (a) A patient suffered a disease that required the pancreas to be removed. Explain the
effect of removing the pancreas on the production of enzymes and hormones, and
subsequently on digestion and blood glucose levels in the individual.

(b) What advice can be given to the patient to help him deal with the health problems
caused by the removal of his pancreas?

7 Figure 1 shows the structure of a nephron and collecting duct.

J

FIGURE 1

(a) Name the process that happens in J.

(b) Name two substances that are not filtered out through the glomerulus.

(c) Explain how the process you named in (a) occurs.

(d) Explain why the fluid flowing in the loop of Henle does not contain glucose even though
glucose is present in Bowman’s capsule.

(e) Mammals have different kidney structures depending on the presence of water in
their habitats. The concentration of urine produced depends on the length of the loop
of Henle. The longer the loop of Henle, the higher the salt concentration in the fluid
surrounding the loop of Henle. Based on this information, what can you predict about
the loop of Henle in animals living in a humid environment compared to animals living in
a dry environment?

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Essay Questions

8 Describe how the body temperature of a worker who has been in a cold room for 6 hours is
regulated.

9  Breathing is an involuntary process that is controlled by the respiratory control centre in the
medulla oblongata. Explain what happens to a climber’s breathing rate when he is at the
peak of a high mountain.

10 Explain the role of erector muscles, fine hair and sweat glands in maintaining the body
temperature on hot days.

11 (a) (i) Explain the importance of maintaining the body temperature at 37 °C.

(ii) Describe two physical ways in which the body reacts to regulate body temperature
after a person bathes with cold water.

(b) In your opinion, what is the effect on urine excretion if the food consumed contains
large quantities of protein?

(c) Explain how the pituitary gland regulates blood osmotic pressure when a person drinks
too little water.

Enrichment

12 Explain how saltwater fish can survive without experiencing dehydration.

13 Why is a urine test conducted to determine if a person has taken drugs?

14 Modern technology has greatly helped patients with kidney problems. For example,
haemodialysis machines have helped many patients with kidney failure to survive. Currently,
research is underway to produce bioartificial kidneys. This device is believed to be able
to carry out all the functions of a healthy kidney. In your opinion, what qualities should a
bioartificial kidney have in order to function like a real kidney?

Complete answers are
available by scanning the
QR code provided

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How are the
fibres of the silk
spider web used
to aid the support
system?

Support and
Movement in
Humans and
Animals14

CHAPTER

•	 What	are	the	types	and	characteristics	of	bones	that	form	the	human	skeleton?
•	 What	are	the	types	of	joints	found	in	the	human	skeletal	system?
•	 How	do	human	arms	and	legs	move?•	 How	do	fish,	birds,	worms	and	grasshoppers	move?
•	 What	are	the	health	issues	related	to	the	human	musculoskeletal	system?

Do you KNOW…

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14.1 Types of Skeletons

14.1.1 List the types of skeletons in
humans and animals:

• hydrostatic skeleton
  • exoskeleton
  • endoskeleton
14.1.2 Justify the necessity of skeletons

in humans and animals.

14.2 Musculoskeletal System of Humans

14.2.1 Identify the bones that form the
human skeletal system:

• axial skeleton
  • appendicular skeleton
14.2.2 Characterise the types of

vertebrae in the backbone:
  •  cervical vertebrae (including the

atlas and axial)
  • thoracic vertebrae
  • lumbar vertebrae
  • sacral vertebrae
  • caudal vertebrae
14.2.3 Compare and contrast

the types of vertebrae.
14.2.4 State the types of joints

in the human skeletal
system:

• immovable joints
  • slightly moveable joints
  • freely moveable joints
14.2.5 Draw, label and explain the

human forearm hinge joint
structure:

• bones
  • cartilages
  • skeletal muscles
  • tendons
  • ligaments
  • synovial membrane
  • synovial fluid

14.3  Mechanism of Movement and
Locomotion

14.3.1 Explain the movement
mechanisms in:

• human forearm
  • human leg (walking)
14.3.2 Describe briefly the locomotion

mechanisms in animals

14.4  Health Issues Related to the Human
Musculoskeletal System

14.4.1 Describe the health issues
related to the human
musculoskeletal system:

• osteoporosis
  • osteomalacia
  • rickets
  • arthritis
  • scoliosis
14.4.2 Justify the practices to maintain

a healthy musculoskeletal
system.

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1 Why do organisms need to
maintain their body shapes?

2 State two functions of the
skeletal system to humans.

3 For animals that move on the
ground, what is the advantage
of having legs below the body
(for example, rats) compared
to having legs at the side of the
body (for example, crocodile)?

14.1Formative Practice

Types of Skeletons14.1

What are the
advantages and
disadvantages
if humans have
exoskeletons like
insects?

Brainstorm!

The skeletal system provides support to humans and animals. There
are three types of skeletons, namely, the exoskeleton, endoskeleton and
hydrostatic skeleton.

Exoskeleton Endoskeleton Hydrostatic skeleton

Types of skeletons

The necessity of skeletal systems in
animals and humans
Humans and animals need the skeletal system to enable them to move
from one place to another in search of food, partners, or to escape from
predators and threats.
Most multicellular organisms need support because of their soft body
tissues. The exoskeleton found in insects and crabs, support and protect
body organs and enable these animals to move. Animals with soft
tissues such as earthworms need a hydrostatic skeleton to maintain a
rigid body shape. The endoskeleton functions to maintain body shape,
support soft body tissues and protect internal organs from injury. You
will learn more about the human skeletal system in the following unit.

ICT 14.1

Activity: Carry out a
brainstorming activity

on the necessity of
support and movement in

humans and animals

Exoskeleton in grasshoppers

Hydrostatic skeleton in
earthworms

14.1.1 14.1.2

Endoskeleton in humans

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Musculoskeletal System
of Humans
Skeletal system
The human skeletal system is made up of the axial skeleton and
appendicular skeleton.

Axial skeleton
The axial skeleton comprises the skull, vertebral column, ribs and
sternum (breastbone).

Appendicular skeleton
The appendicular skeleton includes the pectoral girdle, pelvic girdle,
upper and lower limbs.

14.2

FIGURE 14.1 Human skeletal system

14.2.1

skull

claviclepectoral
girdle

upper limb

lower limb

sternum

ribs

vertebral column

ilium

ischium
pubis

femur

patella

tibia

fibula

phalanges
metatarsals
tarsals

scapula

humerus

ulna

radius

carpus

phalanges

metacarpals

rib cage

pelvic girdle

Axial skeleton

Indicator:

Appendicular
skeleton

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Human vertebral column
The vertebrae (singular: vertebra) on
different parts of the vertebral column
differ in size and shape (Figures 14.2–14.7).
Each vertebra has an opening known as the
neural canal. The spinal cord is located in
the neural canal.

Thoracic vertebrae (Figure 14.2)

•	 Possess a long spinous process

•	 Spinous and transverse processes serve as attachment sites
for muscles and ligaments

•	 The transverse processes (except on the 11th and 12th
thoracic vertebrae) have facets for articulation with the ribs.

Lumbar vertebrae (Figure 14.3)

•	 The biggest and strongest
vertebrae

•	 Possess a short spinous
process

•	 Possess a large centrum to
bear the weight of the lower
back of the body

FIGURE 14.3 Lumbar vertebrae

centrum

caudal

neural
canal

spinous
process

facet

transverse
process

Sacral vertebrae (Figure 14.4)

Five vertebrae fused together
to form a triangular bone

Caudal vertebrae (Figure 14.4)

Four bones fused together to form
a triangular structure which is
pointed at one end.

FIGURE 14.4 Sacral and caudal vertebrae

passage for the
nerves and blood
vessels

cervical
vertebrae

lumbar
vertebrae

process for articulation
with the last lumbar
vertebra

14.2.2

Carry out a
brainstorming
activity to explain
the importance of
skeleton to humans
and animals.

Activity Zone

spinous process

neural canal

facet (articulation with
the vertebra above it)

FIGURE 14.2 Thoracic vertebraecentrum

transverse process

facet (articulation
with the ribs)

sacrum

caudal

thoracic
vertebrae

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Based on the characteristics shown, can you compare and contrast the different vertebrae? What
are the differences between lumbar and thoracic vertebrae? What are the characteristics found on
cervical vertebrae but not found on other vertebrae?

Cervical vertebrae (Figure 14.7)

Possess short spinous process, small centrum,
wide and short transverse process, and a pair of
transverse foramina.

Atlas vertebra (Figure 14.5)

•	 The first cervical vertebra.

•	 The vertebra has a large neural
canal, a small spinous process,
a pair of transverse foramina
(singular: foramen) but with no
centrum.

•	 The vertebra articulates with the
skull.

Axial vertebra (Figure 14.6)

•	 The second cervical vertebra.

•	 The axial vertebrae has a large spinous
process, small transverse process and a pair
of transverse foramina.

•	 It has an odontoid process that articulates with
the facet of the atlas vertebra’s neural canal.

FIGURE 14.5 Atlas vertebra

neural canal

facet

spinous process transverse
process

transverse
foramen

atlas vertebra

axial vertebra

cervical vertebra

FIGURE 14.7 Cervical vertebrae

transverse
process

spinous process

facet

centrum

transverse
foramen

neural canal

14.2.2 14.2.3

All vertebrae have spinous and transverse processes, centrum (except the atlas
vertebra) and neural canal.

SIMILARITY BETWEEN VERTEBRAE

CERVICAL VERTEBRAE

•	 Short spinous process

•	 Wide and short transverse process

•	 Small centrum

•	 A pair of transverse foramina

THORACIC VERTEBRAE

•	 Long spinous process

•	 Long transverse process

•	 Medium-sized centrum

•	 No transverse foramen

LUMBAR VERTEBRAE

•	 Short spinous process

•	 Short transverse process

•	 Large centrum

•	 No transverse foramen

DIFFERENCES BETWEEN VERTEBRAE

FIGURE 14.6 Axial vertebra

spinous process

neural canal
neural arch

odontoid process

transverse
process

transverse
foramen

facet

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How are these bones joined together to form the skeleton? Bones are too
rigid to be bent without breaking. Flexible connective tissues form joints
that hold the bones together so that movement can take place. We will
learn about the different kinds of joints in the following section.

Joints
Joints are points where two or more bones meet, or cartilage and
bones meet. Most joints allow the bones to move relative to each other.
Different types of joints allow different types of movements. The joints
are divided into three types, namely,
•	 immovable joints (for example, suture at the cranium of the skull)

(Figure 14.8)
•	 slightly moveable joints (for example, cartilage discs between the

vertebrae, and cartilage between the first rib and sternum) (Figure 14.9)
•	 freely moveable joints (for example, hinge joint and ball-and-socket

joint) (Figure 14.10)

cartilage disc

vertebra

sternum
clavicle

first rib

cartilage

suture

suture

FIGURE 14.8 Immovable joint
FIGURE 14.9
Slightly moveable joints

Dissect a chicken
wing to observe the
joint’s structure.

Activity Zone

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14.2.4

FIGURE 14.12 Hinge joint at the knee

FIGURE 14.11 Ball-and-socket joint at the hip

The ball-and-socket joint allows rotational movement in all directions
(Figure 14.11). It allows the arm and leg to swing in a circular
motion. Examples of ball-and-socket joints are the shoulder joints
between the humerus and pectoral girdle, and the hip joint
between the femur and pelvic girdle.

BALL-AND-SOCKET JOINT pelvic girdle

femur

The hinge joint allows the movement of bones in one plane
(Figure 14.12). For example, the knee joint allows the lower leg
to swing back and forth, similar to a hinge on a door. The hinge
joint can also be found at the elbow and phalanges of the fingers
and toes.

HINGE JOINTfemur

fibula
tibia

bone
The capsule is the fibrous
tissue that encloses and
provides protection to the joint.

Cartilage serves as a cushion
to the joint, absorbs shocks and
reduces friction between bone
ends. The cartilage also protects
the bones from wearing out.

The synovial fluid serves as a
lubricant that reduces the friction
between the ends of bones.

Freely moveable joints
The ball-and-socket joint and hinge joint are two examples of freely moveable
joints that allow free movements. The general structure of a freely moveable joint
and the functions of its parts are shown in Figure 14.10.

The synovial membrane
secretes synovial fluid into the
synovial cavity.

bone

FIGURE 14.10 Freely moveable joint

PHOTOGRAPH 14.1 Joint

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Movement and Locomotion
The mechanism for the movement of the human forearm involves biceps
and triceps. Figure 14.14 shows the action of both antagonistic muscles
resulting in the movement of the forearm.

14.3

Electroactive plastic
polymer is used to
produce synthetic
muscle. The plastic is
used in the production
of human-like robots
and enables the robots
to walk. The synthetic
muscle contracts in
response to electric
current. It is also used
to help those with
missing limbs.

STEM Bulletin

14.3.1

Skeletal muscle

•	 Comprises bundles of muscle fibres, with a large
supply of nerves and blood vessels

•	 The muscles work in pairs and act in opposite
directions, that is if one muscle contracts, the
other relaxes, and vice versa. These types of
muscles are known as antagonistic muscles.

•	 The biceps and triceps are examples of
antagonistic muscles. The muscle that straightens
the limbs when it contracts is called the extensor.
For example, the triceps. The muscle that bends
the limbs when it contracts is called the flexor.
For example, biceps.

Tendon (connects bone and muscle)

•	 Consists of strong fibres, not elastic but flexible.

Ligament (connects bone to bone)

•	 Bones are held together at the joints by the ligament which consists
of strong, elastic and tough connective tissue bundles.

•	 The ligament provides support and strength to joints and allows
bones to be bent at the joints.

1 Name the bones that form
the axial skeleton of the
human body.

2 State the function of cartilage
and synovial fluid in the joint.

3 State the differences between
the structure and function of
tendon and ligament.

4 Explain the differences
between the ball-and-socket
joint and hinge joint.

14.2Formative Practice

FIGURE 14.13 Skeletal muscle,
tendon and ligament

Apart from joints and bones, support and movement also depend on the
skeletal muscle, tendon and ligament.

humerus

ligamentcartilageulna

radius
synovial
membrane

synovial
fluid

skeletal muscle

tendon

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•	 When the biceps contracts, the pull force is
transmitted to the radius through the tendon.

•	 At the same time, the triceps relaxes.

•	 The radius is pulled upwards, causing the arm
to bend.

ARM BENDING

FIGURE 14.14 The action of the muscles results in the movement of the forearm

14.3.1

What would happen if
(a) you only have the

quadriceps femoris?
(b) the muscle is

attached directly to
the bone?

Brainstorm!

scapula

tendon

humerus

triceps
relaxes

tendon

radius

biceps contracts

ulna
tendonelbow joint

•	 When the triceps contracts, the pull force is
transmitted to the ulna through the tendon.

•	 At the same time, the biceps relaxes.

•	 The ulna is pulled downwards, straightening
the arm.

ARM STRAIGHTENING

The right calf muscle contracts, lifting the heel. The ball
of the foot pushes against the ground.

1

At the same time, the biceps femoris contracts, bending the
foot at the knee joint. The right leg is lifted.

2

As the right leg leaves the ground, the body weight is now supported
by the left leg which is still on the ground. The quadriceps femoris
(extensor) contracts to straighten the leg.

3

The tibialis contracts to bring down the heel. As the right heel touches
the ground, body weight is shifted to the right leg. The whole sequence
is repeated by the left leg.

4

calf muscle

tibialis

FIGURE 14.15 The action of antagonistic muscles during walking

1 2 3 4

biceps relaxes

triceps contracts

quadriceps femoris contracts,
straightening the calf

biceps femoris contracts and
pulls the femur

Leg movement is produced by the action of the antagonistic muscle
pair. The biceps femoris is the flexor whereas the quadriceps femoris
is the extensor (Figure 14.15).

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Mechanism of locomotion in animals

14.3.2

•	 The fish vertebral column is flexible and can be moved from side to side by the contraction and
relaxation of myotome, W-shaped muscle segments.

•	 These antagonistic muscles act in opposite directions. This enables a fish to whip its tail. As the
myotome on the right contracts, the one on the left relaxes.

•	 The tail will be whipped to the right (Figure 14.17).

•	 On the contrary, when the right myotome contracts, the left relaxes and the tail is whipped to the left.

•	 Alternating waves of contraction and relaxation occur along the myotome.

•	 The action causes parts of the body to move from side to side, pushing water backwards and
sideways, and hence moving the fish forward.

•	 The fins are used to control a fish’s movement and direction.

FISH

FIGURE 14.17 Fish locomotion mechanism

Tail movement pushes the
fish forward

Muscles on the right side contract,
pulling the tail to the right

Tail whips to the left

Muscles on the left side
contract, pulling the tail
to the left

Tail whips to the right

FIGURE 14.16 (a) Cross section and (b) longitudinal section of a fish

(a)

myotome

(b)

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wings move up

wings move
down

pectoralis
minor contracts
and pulls the
wing uppectoralis major

contracts and
pulls the wing
down

pectoralis minor
relaxes

air pressure
provides
upthrust

pectoralis minor
relaxes

sternum

FIGURE 14.18 Bird’s locomotion

14.3.2

•	 The action of the large and strong antagonistic muscles on a bird’s
chest assist in the flapping of the wings.

•	 The mechanism of a bird’s wing movement is shown in Figure 14.18.

•	 When the pectoralis major contracts and the pectoralis minor relaxes, the wings
are pulled down.

•	 When the pectoralis minor contracts and the pectoralis major relaxes, the wings
are pulled up.

BIRD (FLIGHT)

The alternate contractions and relaxations of the circular and longitudinal muscles result in
a wave of peristalsis along the body of the earthworm (Figure 14.19).

EARTHWORMS

FIGURE 14.19 Longitudinal and circular muscles of an earthworm

longitudinal muscle

circular muscle

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•	 The antagonistic muscles of a grasshopper, that is the flexor and
extensor are attached to the inner surface of the exoskeleton
(Figure 14.21).

•	 The flexor bends a joint while the extensor straightens it.

•	 The muscular and long hind legs of a grasshopper are adapted for
jumping/leaping (Figure 14.22).

GRASSHOPPER (JUMP/LEAP)

posterior anterior

chaetae

FIGURE 14.21 The flexor and
extensor of the hind leg

The posterior longitudinal muscle contracts
and the circular muscle relaxes; the
earthworm becomes shorter and thicker.

The chaetae at the
posterior segment
anchor to the ground
while the chaetae at the
anterior segment release
their hold of the ground.

The circular muscle at the
anterior segment contracts and
the longitudinal muscle relaxes;
the earthworm becomes longer
and thinner. The anterior segment
(front end) extends forward.

The chaetae at the
anterior segment
anchor to the ground
while the chaetae at
the posterior segment
release their hold of the
ground.

The posterior segment which is
shortened is pulled to the front.

flexor
flexor

exoskeleton

exoskeleton

extensor
extensor

flexor
flexor

exoskeleton

exoskeleton

extensor
extensor

FIGURE 14.20 Locomotion of the earthworm

1

2 3 4

5

FIGURE 14.22 Locomotion of the grasshopper

At rest, the flexor on the hind leg
contracts, pulling the leg towards
the body. In this position, the hind
leg is folded into a Z shape and the
grasshopper is ready to jump/leap.

When the extensor
contracts, the hind
leg is straightened
backwards.

Subsequently, the
catapult-like ejection of
the hind legs projects
the grasshopper forward
and up into the air.

1

2 3
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Health Issues Related to the
Human Musculoskeletal System
The functions of the musculoskeletal system may be affected by disorders
such as osteoporosis (Photograph 14.2), osteomalacia, arthritis and scoliosis.

14.4

(a) Normal bone

(b)  The bone of osteoporosis
patient

PHOTOGRAPH 14.2
(a) Normal bone
(b) The bone of an osteoporosis
patient is thinner, more brittle
and porous.

FIGURE 14.23 Bone mass decreases with age. The symptoms of osteoporosis include fragile
bones, reduced height and stooped posture.

14.4.1

1 In your opinion, why do birds have hollow
bones?

2 Explain how the forearm is moved
upwards.

3 Explain the locomotion mechanism in fish.

4 Describe how a grasshopper performs a
jump/leap.

14.3Formative Practice

Osteoporosis (Figure 14.23) is a bone disorder characterised by weak
bones that may break easily. As a person ages, the rate of calcium
loss is higher compared to the rate of calcium absorption, causing a
loss in bone mass or density. Among the contributing factors are lack
of exercise and low intake of calcium, phosphorus and vitamin D.
Osteoporosis is common among women who reach menopause
because their oestrogen level is decreased.

Oestrogen is involved in calcium metabolism whereby it helps the body
to absorb calcium and reduces calcium loss from the bone.

A low oestrogen level can reduce bone density due to the loss of
calcium from bones (Photograph 14.2).

OSTEOPOROSIS

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The vertebral column of a
normal individual

The vertebral column of a
scoliosis patient

vertebral column

14.4.1

FIGURE 14.24 Normal bone and the bone of a rickets patient

Work in a group and
gather information
on osteoporosis,
osteomalacia, rickets,
arthritis and scoliosis.
Conduct a scientific
study on treatments
that may help
individuals with health
issues related to the
skeletal muscle.

Activity Zone

Build a walking aid
for an individual with
issues of muscle injury
and joint pain.

Activity Zone

Osteomalacia is a soft bone condition due
to lack of calcium, phosphorus and vitamin D.
Osteomalacia occurs among adults, especially
pregnant women. It is called rickets if it occurs
among children (Figure 14.24). Rickets causes
the softening and weakening of children’s
bones, resulting in bone defects.

OSTEOMALACIA

A common type of arthritis among the
elderly is osteoarthritis. Osteoarthritis is
caused by decreased synovial fluid, and
wear and tear of the cartilage in certain joints
(Photograph 14.3). The cartilage becomes
thinner, and the ligament shortens and loses
some of its elasticity. Joints, such as the
knee joint becomes swollen, painful and less
flexible. Arthritis restricts daily activities such
as walking.

ARTHRITIS

The backbone of a scoliosis patient is bent to the side, forming an ‘S’
or ‘C’ shape when viewed from the back (Figure 14.25). Scoliosis may
be caused by a genetic factor or abnormal growth of the backbone
during puberty development.

SCOLIOSIS

FIGURE 14.25 Normal
vertebral column and the
vertebral column of a
scoliosis patient

normal rickets
patient

What is the appropriate treatment to help individuals who experience
health issues related to the musculoskeletal system?

PHOTOGRAPH 14.3 (a) Normal joint (b) Deteriorating joint due
to osteoarthritis

(a) (b)

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Practices to maintain a healthy
musculoskeletal system
The following are practices to care for the musculoskeletal system.

GOOD BODY POSTURE

Posture refers to a person’s body position when sitting, lying,
walking and standing. We should not slouch when standing
or sitting. Slouching will exert pressure on the vertebral
column, resulting in the misalignment of the vertebral column.
This will prevent circulation of the blood, suppressing the
nerves and vital organs.

Good posture when using a computer

14.4.2

PROPER ATTIRE

Wear proper, comfortable and loose clothing so
as not to restrict blood circulation and affect the
musculoskeletal system. A suitable pair of shoes,
with low heels and cushion, provides support and
prevents injury to the vertebral column.

EXERCISE

Exercise strengthens the joint structure and
increases the flexibility of muscles and ligaments.
Exercise also increases bone strength and bone
mineral deposits among adults, as well as prevents
osteoporosis in the elderly.

BALANCED DIET

Consume a balanced diet,
especially foods rich in calcium
(milk), minerals (phosphate),
vitamin C and D. Vitamin D
aids in calcium absorption,
while vitamin C increases
bone mass.

Wear comfortable
attire and shoes

Kerjaya Milenia

Orthopaedics is a specialised medical
field that focuses on the diagnosis, care
and treatment of the musculoskeletal
system. Doctors who specialise in this
field are called orthopaedic surgeons.

Millennial Career

Engage in various sport
activities

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14.4.2

1 Suggest two ways to care for the
musculoskeletal system.

2   As a doctor, explain ways to help
scoliosis patients go through normal
daily life.

3 Define osteoporosis and explain the
measures that should be adopted at a young
age to prevent osteoporosis at old age.

4 Explain three practices that can help
maintain a healthy musculoskeletal system.

14.4Formative Practice

Headache

Shoulder and
neck pain

Breathing
difficulty and

back pain

FIGURE 14.26 Effects as a result of incorrect body posture when using smartphones

Discuss the effects
of the following
practices on the
musculoskeletal
system:
(a)  Wearing

high-heeled shoes
(b)  Sitting with your

wallet in your back
pocket

(c)  Carrying a heavy
bag

(d)  Incorrect body
posture when using
smartphones and
computers

Activity Zone

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Have you mastered the following important concepts?
•	 The types of skeleton in humans and animals
•	 Axial and appendicular skeletons
•	 Types of vertebrae in the vertebral column
•	 Types of joints in the human skeletal system
•	 Hinge joint structure
•	 How humans move their arms and legs when walking
•	 The	locomotion	mechanisms	of	animals	such	as	earthworms,	grasshoppers,	birds	and	fish
•	 Health issues related to the human musculoskeletal system
•	 Practices to maintain a healthy musculoskeletal system

Types	of
Skeleton

Human	Musculoskeletal
System

Mechanisms	of	movement
and	locomotion

SUPPORT AND MOVEMENT IN HUMANS AND ANIMALS

•	Hydrostatic
skeleton

•	Exoskeleton
•	Endoskeleton

Mechanisms of movement
•	Human	forearm	(biceps	and	triceps)
•	Human	leg	(biceps	femoris	and
quadriceps	femoris)

Mechanisms of movement in animals
•	Fish	–	myotome
•	Birds	–	pectoralis	major	and
pectoralis	minor

•	Earthworms	–	circular	and
longitudinal	muscles

•	Grasshopper	–	flexor	and	extensor

Practices in caring for the musculoskeletal system:	exercise,
balanced	diet,	good	body	posture	and	proper	clothing	and	shoes.

Axial skeleton:
skull,	vertebral	column,
ribs	and	sternum

Appendicular
skeleton:
pectoral	girdle,
pelvic	girdle,	upper
and	lower	limbs

Types of joints:
immovable	joints,
slightly	movable
joints,	freely
movable	joints

Joint structure:	bones,
cartilage,	skeletal	muscle,
tendon,	ligament,
synovial	membrane	and
synovial	fluid

Summary

Self Reflection

Health	Issues

Osteoporosis,	rickets,	scoliosis,	osteomalacia,	arthritis

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1 State the differences between cervical and thoracic vertebrae.

2 Figure 1 shows the locomotion of an earthworm.

direction of movement

T segment
S segment

FIGURE 1

Explain the muscle action in segments T and S that enables the earthworm to move in the
direction shown.

3 Why is it important for an organism to maintain its shape?

4 Describe the meaning of good posture. Why must we always practise good posture while
doing any activity?

5 Explain why muscle contractions require adequate blood supply.

6 Figure 2 shows two types of vertebrae,
X and Y in the human vertebral column.

(a) Name vertebrae X and Y.

(b) Explain the role of vertebrae during body
movement.

(c) Relate the thoracic vertebrae to the
breathing mechanism.

7 Figure 3 shows muscles P and Q, bone Y and tissue X
that are involved in the forearm movement.

(a) Name muscle P and Q, bone Y and tissue X.

(b) State two characteristics of tissue X that enable it to
function.

(c) If tissue X is torn due to an accident, what problems
will the victim face?

(d) Suggest a suitable food for a person with fractured
bone Y. In your opinion, explain why this particular
food is presumed suitable for the individual.

(e) Explain how all the parts labelled in Figure 3 react in the condition shown.

Summative Practice 14

bone Y

muscle Q
muscle P

tissue X

FIGURE 3

FIGURE 2
X Y

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Essay Questions

8 Figure 4 shows a human movement.

tendon
bone

knee

biceps femoris
quadriceps
femoris

calf muscle

FIGURE 4

Based on Figure 4, describe how muscles, bones, tendons, ligaments and joints enable the
above movement to happen.

9 Describe how the earthworm and fish skeletal systems are adapted for locomotion in their
respective habitats.

10 (a) Explain the property of muscles involved in human movement.

(b)  (i)  Explain the measures that can be practised to maintain a healthy musculoskeletal
system.

(ii)  Describe the factors that may put an individual at a high risk of developing
osteoporosis.

(c) Describe how muscles work together with the ligament and tendon to move the
forearm.

Enrichment

11 The long bones in mammals are not compact but hollow. Explain the advantages of hollow
bones.

12 Birds fly using wings. The wing movement allows birds to exert an upthrust. However, the
ability of birds to fly not only depends on its wings but also its support system. Explain how
the support system helps birds to fly.

13 The latest research in treating bone fracture includes the use of materials such as carbon
nanotube that serves as a scaffolding for bone tissue growth. If you are a scientist looking
for new material to treat damaged bones, what are the characteristics that the material
should have in order to replace broken bones?

Complete answers are
available by scanning the
QR code provided

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15
CHAPTER

Sexual
Reproduction,
Development and
Growth in Humans
and Animals

How does modern
technology help in
conception?

•	 What	are	the	features	of	the	anatomical	system	of	human	reproduction?
•	 How	is	gamete	formed?
•	 How	does	the	period	cycle	happen?
•	 How	does	the	development	of	the	human	foetus
happen?

Do You KNOW…

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15.1 Reproductive System of Humans

15.1.1  Characterise the anatomy of the:
  • male reproductive system
  • female reproductive system

15.2 Gametogenesis in Humans

15.2.1 Justify the necessity of
gametogenesis.

15.2.2 Describe gamete formation:
  • spermatogenesis
  • oogenesis
15.2.3 Identify the structure of:
  • sperm
      – head
      – middle piece

– tail
  • Graafian follicle
   – secondary oocyte
      – follicular cells
15.2.4 Compare and contrast between

spermatogenesis and oogenesis.

15.3 Menstrual Cycle

15.3.1 Analyse the changes in the levels of
hormones involved during:

• menstruation
  • follicle development
  • thickening of the endometrium
  • ovulation
  • corpus luteum formation
15.3.2 Correlate the changes in the levels

of hormones involved with:
  • pregnancy
  • miscarriage
15.3.3 State the meaning of premenstrual

syndrome and menopausal
syndrome

15.4 Development of a Human Foetus

15.4.1 Describe the fertilisation process
and the formation of zygotes.

15.4.2 Make a sequence and explain the
early development of an embryo
until implantation:

• two-celled embryo
  • morula
  • blastocyst

15.4.3 Explain the role of human chorionic
gonadotropin (HCG) hormone in the
early stages of pregnancy.

15.4.4 Communicate about the roles
of following structures in the
development of a foetus:

• placenta
  • umbilical cord
15.4.5 Justify the necessity for separate

foetal and maternal blood
circulatory systems.

15.5 Formation of Twins

15.5.1 Describe the processes in the
formation of twins:

• identical twins
  • fraternal twins
15.5.2 Compare and contrast identical

and fraternal twins.
15.5.3 Correlate cellular division with the

formation of conjoined twins.

15.6 Health Issues Related to the Human
Reproductive System

15.6.1 State the meaning of impotency.
15.6.2 Communicate about causes of

human impotency.

15.7 Growth in Humans and Animals

15.7.1 Explain the meaning of growth in
organisms.

15.7.2 Determine parameters to measure
growth in humans and animals.

15.7.3 Describe the growth of insects with
exoskeleton:

• complete metamorphosis
  • incomplete metamorphosis
15.7.4 Analyse the growth phases on

sigmoid growth curves of humans
and animals.

15.7.5 Analyse the intermittent growth
curve of animals with exoskeletons.

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Reproductive System of Humans
The male and female reproductive system
The continuity of a species is dependent on the increase in population
through the process of sexual or asexual reproduction. Sexual
reproduction involves the production of male and female gametes by
individuals who have reached sexual maturity. This process is completed
with the fertilisation of both gametes to create new life. The structure
and function of the male and female reproductive systems are shown in
Figure 15.1 and Figure 15.2 respectively.

15.1

FIGURE 15.1 Female reproductive system

15.1.1

•	 The uterus is an organ with thick
muscular walls.

•	 The inner wall of the uterus is lined with
endometrium tissue, which secretes
mucus and is rich in blood vessels.

•	 Embryo implants in the endometrium.

•	 The endometrial tissue which is thick
and rich in blood vessels supplies the
embryo with nutrients and oxygen.

UTERUS

A canal where sperms enter,
and also serves as a passage
for birth and menstruation.

VAGINA

The female reproductive
organ that produces ovum
(female gamete, plural: ova)
and the female sex hormones,
which are oestrogen and
progesterone.

OVARY

Narrow opening to the uterus which
secretes mucus to help sperm swim
up to the Fallopian tubes.

CERVIX

•	 A thin, muscular tube.

•	 The inner wall is lined with cilia.

•	 The action of the cilium,
combined with the peristalsis
of the Fallopian tube, helps in
delivering the secondary oocyte
or embryo to the uterus.

FALLOPIAN TUBE

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FIGURE 15.2 Male reproductive system

1 State the structures of the male reproductive
system.

2 Explain the functions of the seminal vesicle
and the scrotum.

3 State the structures of the female
reproductive system.

4 Explain the functions of the Fallopian tube
and uterus.

15.1Formative Practice

Secretes fluid filled with
nutrients for the sperms.

SEMINAL VESICLE

Secretes a fluid that helps in
sperm movement.

PROSTATE GLAND

A sac-like structure that holds
and protects the testis.

SCROTUM

Sperm is transported through
the sperm duct (vas deferens).

SPERM DUCT

A tube for the discharge of
sperm and urine from the
body.

URETHRA

•	 Located within the scrotum.

•	 Produces sperm (male
gametes) and the male sex
hormone, testosterone.

TESTIS

15.1.1

•	 The male sexual organ that is
rich in soft tissues and blood
vessels.

•	 Releases sperm into a
female’s vagina during
copulation.

PENIS

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Primordial germ cells will undergo cell division
to produce sperm. Sertoli cells within the
walls of the seminiferous tubules provide

nutrients throughout this process. Sperm is
transported from the seminiferous tubules
to the epididymis and flows out through
the sperm duct (vas deferens).

Spermatogenesis is stimulated by
the follicle-stimulating hormone
(FSH) and testosterone. This
process is also aided by the
luteinizing hormone (LH) which
stimulates testosterone secretion
in the testes.

FIGURE 15.3 Longitudinal section of the testes

Gametogenesis in Humans
The necessity of gametogenesis
The production process of reproductive cells (gametes) is called
gametogenesis. This process takes place in the gonads, which are the
testes in males, and the ovaries in females. Gametogenesis produces
gametes that are haploid (n). When fertilisation takes place, the nucleus
of the sperm will fuse with the nucleus of the ovum in the Fallopian tube
to form a diploid zygote (2n).

Spermatogenesis
Spermatogenesis is a process of sperm production that
takes place in the seminiferous tubules. Figure 15.3
shows a longitudinal section of the testes.

15.2

15.2.1 15.2.2

seminiferous tubules

sperm duct
(vas deferens)

Each seminiferous tubule consists of primordial
germ cells.

epididymis Figure 15.4 summarises the
spermatogenesis scheme.

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2n

2n 2n

2n 2n 2n 2n

2n

n n

n n n n

n n n n

2n

2n 2n

2n 2n 2n 2n

2n

n n

n n n n

n n n n

primary
spermatocytes

secondary
spermatocytes

spermatid

sperm

meiosis I

meiosis II

differentiation

FIGURE 15.4 Spermatogenesis

Primordial germ cells divide mitotically to
form diploid spermatogonium.

Each primary spermatocyte undergoes
meiosis I to form two secondary
spermatocytes (haploid).

Each secondary spermatocyte
undergoes meiosis II to produce two
haploid spermatids.

15.2.2

2n

2n 2n

2n 2n 2n 2n

2n

n n

n n n n

n n n n

2n

2n 2n

2n 2n 2n 2n

2n

n n

n n n n

n n n n

2n

2n 2n

2n 2n 2n 2n

2n

n n

n n n n

n n n n

primordial germ sel

repetitive mitotic
divisions

development

spermatogonium

MULTIPLICATION PHASE

GROWTH PHASE

MATURATION PHASE

Spermatids then undergo
differentiation to form sperms.

Spermatogonium expands to form
primary spermatocytes (diploid).

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2n

2n

2n

n n

n

nnnn

Oogenesis
Oogenesis is the process of secondary oocyte or female gamete production (Figure 15.5). This
process takes place in the ovaries. Unlike spermatogenesis, oogenesis begins in a female’s ovaries
before they are born.

2

FIGURE 15.5 Oogenesis

BEFORE BIRTH

15.2.2

primordial
germ cell

mitosis

oogonium

development

primary oocytes

primary oocytes primary follicle

meiosis I
completed

secondary oocytes (n)

ovulation

sperm

corpus
luteumovum

meiosis II

polar bodies die

released secondary
oocyte

secondary follicle

Graafian follicle

infant and
childhood stage

every month starting
from puberty until
menopause

1 Primordial germ cells undergo mitotic division
multiple times to form oogonium (diploid).

Oogonium develops into primary oocyte which
is encapsulated with one or more layers of follicular
cells, forming primary follicles. The growth of
the follicle is stimulated by the follicle-stimulating
hormone (FSH). Primary oocyte then undergoes
meiosis but the process stops at prophase I during
fetal development.

8 After ovulation, the remaining
follicle forms corpus luteum.

first polar
body (n)

AFTER BIRTH

PUBERTY

2n

2n

2n1

2

3

4
5

6

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15.2.2

without
fertilisation

upon
fertilisation

3 At birth, a baby girl already has millions of primary oocytes that remain dormant in prophase I
meiosis I. The number of oocytes will decrease at puberty.

4 Upon reaching puberty, the primary oocytes will continue meiosis I to form secondary
oocyte and a first polar body. Secondary oocyte will begin meiosis II which is then halted at
metaphase II. The first polar body will complete meiosis II and form two second polar bodies.

7 The secondary oocyte (immature ovum) will complete meiosis II once a sperm
penetrates it. Meiosis II produces ovum (n) and first polar body (n). Fertilisation takes
place when the sperm nucleus fuses with ovum nucleus and produces a diploid zygote
(2n). The rest of the polar bodies will die and will be disintegrated by the ovary.

5 A layer of follicular cells envelops the secondary oocyte and is called secondary
follicle. The secondary follicle will then develop into the Graafian follicle, which
releases oestrogen.

6 A mature Graafian follicle will approach the surface of the ovary and release a
secondary oocyte into the Fallopian tube. This process is called ovulation.

9 Corpus luteum continues to grow and
secretes oestrogen and progesterone.

10 Corpus luteum and secondary oocyte degenerate and
dies, and then is removed through menstruation.

secondary follicle

primary oocyte

Graafian follicle

secondary oocyte

corpus luteum

primary follicle

FIGURE 15.6 Oogenesis in the ovaries

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Differences

It takes place in the testis. It takes place in the ovaries.

Spermatogonium (diploid) produces four sperms
(haploid) after meiosis.

Oogonium (diploid) only produces one functional
secondary oocyte (haploid) and three non-
functioning polar bodies after meiosis.

Sperms are smaller and made up of the midpiece,
head and tail.

Secondary oocytes are large and spherical in
shape.

After meiosis I, two secondary spermatocytes are
produced.

After meiosis I, one secondary oocyte and one
polar body is produced.

Meiosis is completed.
Meiosis II is only completed when a sperm fertilises
the secondary oocyte.

Spermatids undergo differentiation to become
sperms.

Secondary oocyte does not undergo differentiation.

The production of sperm is continuous from
puberty until old age.

The production of the secondary oocyte is not
continuous. It starts in the female foetus and
remains dormant when the baby is born. The
process continues once the female reaches
puberty and stops during menopause.

Millions of sperms are formed every day.
Only one secondary oocyte is released from the
ovaries at every menstrual cycle.

Structure of sperm and Graafian follicle

The comparison between spermatogenesis and oogenesis
The comparison between spermatogenesis and oogenesis are summarised in Table 15.1.

TABLE 15.1 The comparison between spermatogenesis and oogenesis

follicle
cells

secondary
oocyte

A secondary oocyte is a large cell that is
surrounded by a gel-like substance and follicular
cells. The secondary oocyte and follicular cells
will form the Graafian follicle.

FIGURE 15.8 Graafian
follicle

tail

midpiece

head

FIGURE 15.7 Sperm

A sperm has three main parts: head, midpiece and tail. The head
contains a nucleus whereas the midpiece is packed with mitochondria which
generates energy for the sperm to swim to the Fallopian tube for fertilisation.

Spermatogenesis Oogenesis

Similarities

•	 Both are the processes of gametogenesis that take place in the reproductive organs.
•	 Produce gametes that are haploid which are involved in fertilisation.

15.2.3 15.2.4292

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TABLE 15.2 Functions of hormones in a menstrual cycle

Gland Hormone Function

Pituitary Follicle-
stimulating
hormone (FSH)

•	 Stimulates follicle growth in the ovary.

•	 Stimulates the release of oestrogen.

Luteinizing
hormone (LH)

•	 Stimulates ovulation.

•	 Causes the formation of the corpus
luteum.

•	 Stimulates the release of progesterone.

Ovary

Oestrogen

•	 Repairs and stimulates the thickening of
the endometrium.

•	 Stimulates follicle growth until it matures.

•	 Stimulates FSH and LH release prior to
ovulation.

Progesterone

•	 Stimulates the thickening of the
endometrium, making it thick, folded and
rich in blood vessels to prepare for the
implantation of embryo.

•	 Stops the release of FSH and LH to
prevent follicle growth and ovulation.

Changes in hormonal level, follicle growth, and changes in endometrial
wall thickness throughout one menstrual cycle are shown in Figure 15.9.

15.3.1

Menstrual Cycle
Role of hormones in menstrual cycle15.3

One of the side
effects of low
oestrogen is
calcium loss in the
body which leads
to a reduction
in bone density,
making it porous
and weak. This
condition is called
osteoporosis.

Biological Lens

Kerjaya Milenia

Obstetricians and
gynaecologists are
specialists in female
reproduction and
women’s health.

Millennial Career

The menstrual cycle involves the production of a secondary oocyte and
thickening of the endometrial wall throughout one cycle. In this cycle, the
endometrium will become soft, thick and rich with blood vessels. This is
to prepare the endometrium for embryo implantation. If fertilisation does
not take place, the secondary oocyte will die and the endometrium wall
will shed. This will lead to bleeding known as menstruation.

MENSTRUAL CYCLE

The functions of hormones in a menstrual cycle is shown in Table 15.2.

1 What could possibly happen if
gametogenesis does not take place?

2 Explain three differences between
spermatogenesis and oogenesis.

15.2Formative Practice

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FOLLICLE DEVELOPMENT

CHANGES IN ENDOMETRIAL
THICKENING

HORMONE LEVEL

FIGURE 15.9 Stages of events and hormonal level changes in one menstrual cycle

15.3.1

Graafian follicle secondary oocyte

Ovulation Corpus luteum
degenerates

Corpus
luteum

Development of
secondary follicle/

Development of primary
follicle

Days of menstrual cycle

Menstruation

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 days

FSH

LH

oestrogen

progesterone

hormone
level

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• Before a menstrual cycle begins, the level of hormones is low. With the absence of stimulation
from progesterone and oestrogen, the thickened endometrium will shed and menstruation
will begin (first day).

•	 A menstrual cycle begins a day before menstruation when the hypothalamus releases the
gonadotrophin-releasing hormone (GnRH).

•	 GnRH stimulates the pituitary gland to release the follicle-stimulating hormone (FSH) and
luteinizing hormone (LH) into the blood.

•	 FSH stimulates follicle growth in the ovary. Within the primary follicle, the oocyte grows into
the secondary oocyte, which is contained within the Graafian follicle.

•	 Growing follicles release oestrogen.

•	 Oestrogen encourages follicle maturation and also encourages endometrial wall repair.

•	 Low levels of oestrogen inhibit the release of FSH and LH via a negative feedback mechanism,
which in turn prevents the growth of new follicles.

DAY 0–5

• Oestrogen level rises and peaks on day 12, stimulating the hypothalamus to secrete GnRH via
a positive feedback mechanism.

• A high level of GnRH then stimulates the pituitary gland to secrete more FSH and LH.

• The LH level rises until it peaks on day 13, leading to ovulation and release of a secondary
oocyte from Graafian follicle on day 14.

• LH also stimulates the follicular tissue left behind to transform into the corpus luteum.

DAY 6–14

• LH stimulates the corpus luteum to secrete oestrogen and progesterone.

• The combination of oestrogen and progesterone inhibits the release of FSH and LH from the
hypothalamus via negative-feedback mechanism so as to stop the growth of new follicles.

• Progesterone stimulates endometrial wall thickening, enriching it with blood vessels in
preparation for embryo implantation, in the event that fertilisation takes place.

DAY 15–21

• If fertilisation does not take place, decreasing LH levels will cause the corpus luteum to
degenerate, which in turn stops the secretion of oestrogen and progesterone.

• Without stimulation from oestrogen and progesterone, the endometrium will shed and
menstruation will begin.

• Low levels of progesterone and oestrogen will no longer inhibit the hypothalamus and pituitary
gland, making way for GnRH to be secreted again, which then stimulates secretion of FSH and
LH. A new menstrual cycle will begin with new follicle growth.

• If fertilisation occurs, the corpus luteum will continue to grow and secrete progesterone and
oestrogen.

• This will cause the endometrial wall to continually thicken in order to support foetal growth.

DAY 22–28

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Role of hormone in pregnancy and
miscarriage
The corpus luteum will continue to produce oestrogen and progesterone
up to three to four months after pregnancy. Thereafter, the corpus luteum
will degenerate, and the production of oestrogen and progesterone will
be taken over by the placenta until birth.

Progesterone inhibits the secretion of FSH and LH. Therefore,
the menstrual cycle and ovulation do not occur throughout a

pregnancy.
The imbalance of progesterone and oestrogen levels may

lead to a miscarriage, due to the decrease of progesterone
level which causes the uterus to shrink.

15.3.2 15.3.3

Premenstrual syndrome or symptoms that appear prior to a
menstrual cycle usually manifests between 7 to 14 days before the first

day of the menstrual cycle. This syndrome occurs due to the imbalance
of oestrogen and progesterone hormones within the menstrual cycle.

Menopause occurs within the ages of 46 to 50 years old, when
ovulation and menstruation stop naturally. The increase in age
leads to reduced secretion of progesterone and oestrogen,
which then causes reduced stimulation of FSH and LH on the
ovaries.

At this stage, the ovaries stop producing ovum. After
menopause, a woman is not able to conceive a child anymore.

PREMENSTRUAL SYNDROME (Photograph 15.1)

MENOPAUSE (Photograph 15.2)

PHOTOGRAPH 15.1
Premenstrual syndrome symptoms

PHOTOGRAPH 15.2
Menopausal symptoms

Bad temper

Fatigue

Difficulty sleeping

Hot flushes

Low mood

Bad temper

Headache

Emotional
instability

Premenstrual syndrome and
menopausal syndrome

1 State the hormones involved in the
menstrual cycle and their functions.

2 Explain the functions of progesterone and
its effects on pregnancy.

3 Explain what would happen to the
corpus luteum if fertilisation does
not occur.

4 In your opinion, what is the best way
to overcome premenstrual syndrome?

15.3Formative Practice

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Development of a Human
Foetus
The process of fertilisation
Fertilisation can occur when one out of the millions of sperm succeeds
in penetrating the secondary oocyte in the Fallopian tube. This is
followed by changes to the secondary oocyte’s membrane that prevents
penetration from other sperms. Then, fertilisation occurs when the
sperm nucleus fuses with the ovum nucleus to form a diploid zygote.

Early development of an embryo until
implantation

15.4

AR

Each semen
ejaculation
contains between
300 to 500 million
sperms. However,
only about 300
to 500 sperms
successfully reach
the secondary
oocyte in the
Fallopian tube.

Biological Lens

15.4.215.4.1

implantation of
the blastocyst

morula
8 cells4 cells2 cells

fertilisation

zygote

unfertilised
secondary oocyte

ovary

FIGURE 15.10 Early development of an embryo and implantation of a blastocyst

endometrium

the thickened blastocyst wall
will develop into embryo

blastocyst

•	 While travelling down the Fallopian tube, the zygote undergoes
multiple divisions through mitosis.

•	 The first cell division produces a two-cell embryo. The following cell
divisions will finally produce a morula.

•	 The morula then transforms into a blastocyst (Figure 15.10).

•	 The blastocyst will then implant in the endometrium. This process is
called implantation. The blastocyst continues to grow into an embryo.

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The umbilical cord is a tube that contains the umbilical vein and
umbilical arteries.
•	 The umbilical vein carries blood rich in oxygen and nutrients

from the placenta to the foetus.
•	 Umbilical arteries carry deoxygenated blood (rich in carbon

dioxide) and nitrogenous waste such as urea from foetus to the
placenta.

PHOTOGRAPH 15.3
Pregnancy test detects HCG
in urine

15.4.3

Role of human chorionic gonadotropin
(HCG) hormone
The placenta also produces the human chorionic gonadotropin (HCG)
hormone during pregnancy. The level of this hormone increases at the
early stages of pregnancy and will double every two to three days for
the first four weeks of pregnancy. The main function of HCG is to
ensure that the corpus luteum continues to secrete oestrogen and
progesterone in the early stages of pregnancy. This hormone can be
detected in the urine of pregnant mothers.

Role of placenta and umbilical cord in
foetal development
The placenta is formed from the mother’s endometrial tissue and
embryonic tissue. It is connected to the foetus through the umbilical
cord which contains blood vessels that carries substance in and out of
the foetus.

15.4.4

umbilical vein

umbilical arteries

maternal blood

foetal blood capillaries

umbilical cord

FIGURE 15.11 Placenta and umbilical cord
placenta

placenta

foetal blood vessels

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15.4.515.4.4

The placenta is the exchange site of substances between mother and
foetus.

•	 Glucose, amino acids, hormones, antibodies and oxygen are
absorbed from the mother’s blood into the foetal blood capillaries.

•	 Carbon dioxide and nitrogenous waste such as urea are absorbed
from the foetal blood capillaries into the mother’s blood circulation.

The placenta also acts as an endocrine organ that secretes hormones
during pregnancy.

•	 In the fourth month of pregnancy, the corpus luteum will degenerate
and no longer secrete progesterone.

•	 The placenta will replace corpus luteum in producing progesterone
and oestrogen needed to maintain endometrial thickness.

Importance of placenta

Foetal and maternal blood
circulatory systems
The blood of the mother and the foetus do not mix as they are
separated by a thin membrane. This is important because:
(a) It protects the foetus from certain dangerous chemical

substances such as toxins and bacteria that can be
absorbed into the foetal blood circulation.

(b) It prevents the thin foetal blood vessels from bursting
due to the mother’s high blood pressure.

(c) It prevents agglutination or blood clots from
happening in the foetus, as the foetus might not be of
the same blood group as the mother.

The thin membrane layer is not able to prevent certain
substances from being absorbed, such as drugs and
medication, cigarette smoke and alcohol ingested by the
mother. Viruses such as HIV and rubella can also cross the
placenta and be absorbed into the foetal blood circulation,
which may disrupt the foetal development.

1 Explain the early developmental process of
the embryo.

2 What is the main function of the HCG
hormone?

3 Describe the function of the placenta.

4 State what might happen if maternal blood
mixes with foetal blood.

15.4Formative Practice

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(b) FRATERNAL TWINS

Formation of Twins
Process of twin formation
Twins refer to two or more children that are born from one pregnancy.
There are two types of twins:
•	 identical twins
•	 fraternal twins

15.5
(a) IDENTICAL TWINS

FIGURE 15.12 Development of (a) identical twins and (b) fraternal twins

15.5.1

1 placenta shared
with 2 foetus

1 placenta shared
with 2 foetus

2 sperms
2 ova

two separate
embryos are
formed

two sperms
fertilise two
ova

separate placentas

one sperm
fertilises one
ovum

embryo divides
into two

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Differences between identical and fraternal twins

Identical twins Fraternal twins

Product of fertilisation of one ovum and one
sperm forming one zygote.

Product of fertilisation of two sperms and two ova
forming two zygotes.

Embryo divides into two. Embryo does not divide into two.

One placenta is shared between two foetus. Each foetus has its own placenta.

The genetic makeup and physical appearances of
these twins are similar as they are from the same
zygote.

The genetic makeup and physical appearances
of these twins are different as they are from two
different zygotes.

The sex of both twins is the same. The sex of both twins may be the same or different.

Development of conjoined twins
Conjoined twins develop when there is incomplete
division of the embryo in identical twins. Although
two foetuses are formed from the embryo, some
of their physical parts are still fused together,
usually the chest, abdomen or buttocks.
Conjoined twins may also share one or two
internal organs.
The life of conjoined twins may be difficult
as they must always be together. They also do
not have any time alone. Their movements are
limited due to their physical state.
Most conjoined twins die before they are born
or have short lifespans. They may be able to be
separated through surgery. However, the success of
surgery depends on the joined part and what internal
organs are shared between them.

15.5.2 15.5.3

PHOTOGRAPH 15.4 Conjoined twins

1 State two differences between identical and fraternal twins.

2 State the characteristics of conjoined twins.

15.5Formative Practice

TABLE 15.3 Differences between identical and fraternal twins

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15.6.215.6.1

What are the benefits
and drawbacks
of science and
technological
contributions to human
reproduction? What
moral issues are related
to the application
of technological
reproduction? Discuss.

Activity Zone

What are the causes of impotency?

15.6Formative Practice

Health Issues Related to the
Human Reproductive System
Impotency
Impotency occurs when a husband and wife are unable to conceive. The
cause of this might be from the husband or wife, or both.

15.6
Testes do not
produce sperm

Erectile
dysfunction

Hormonal
imbalance Low sperm

count
Low quality sperm/
abnormal sperm

Ovaries do not
produce secondary
oocyte

Growth in
the uterus

Blocked
Fallopian tubes

Hormonal
imbalanceAbnormal

uterus

•	 Hormonal imbalance can be treated with hormonal therapy.

•	 Blocked Fallopian tubes or blocked sperm ducts can be treated via
surgery.

•	 In	vitro fertilisation (IVF) can be used for women who have blocked
Fallopian tubes.

TREATMENT FOR IMPOTENCY

CAUSES OF MALE IMPOTENCY

CAUSES OF FEMALE IMPOTENCY

FIGURE 15.13 Causes of male impotency

FIGURE 15.14 Causes of female impotencyICT 15.1

Video: IVF
(Accessed on 21 August

2019)

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Growth in Humans and
Animals15.7

Growth in organisms
Growth in organisms is an irreversible, permanent process
that involves the increase in the number of cells, size, volume
and weight of the organism’s body. Growth also involves
differentiation and cell specialisation as well as specialising the
shapes and functions of cells. Growth in organisms is important
for the development and maturation of bodily systems.

Measuring growth in humans
and animals
The parameters that are used in measuring growth are:
(a) Increase in size or volume, for example, changes in

height or length of an organism
(b) Changes in fresh weight or dry weight:
 (i)  Dry weight refers to the weight of an organism

after all the fluid is removed from its body. This is
done by weighing the organism after it has been
dried in the oven at 100 °C repeatedly until the
weight remains the same. The weakness of this
parameter is that the organism has to be killed.
However, this method is suitable for plants.

(ii)  Fresh weight can be taken whenever and organisms
do not need to be killed. However, this method is
less accurate because the amount of fluid in the
body is dependent on the organism’s fluid intake.
This parameter is measured for a certain amount
of time.

Growth of Insects
Organisms with exoskeletons like insects undergo growth
differently. Insects go through two different types of growth
which are complete metamorphosis and incomplete
metamorphosis.

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15.7.3

FIGURE 15.16 Incomplete metamorphosis

Insects like butterflies undergo complete metamorphosis. In complete
metamorphosis, there are four different stages of growth, which are egg,
larvae, pupa and adult. Figure 15.15 shows complete metamorphosis.

egg

INCOMPLETE
METAMORPHOSIS

nymph

nymph

casts off outer cuticle
during ecdysis

ecdysisadult
grasshopper

COMPLETE
METAMORPHOSIS

egg

caterpillar (larvae)

The caterpillar starts to
become a pupa.

Nymph (young insect) hatches
from egg

Ecdysis occurs a few
more times until the
insect becomes an adult

Rapid development
at this stage.

pupa

adult butterfly

The butterfly matures
into an adult butterfly.

A caterpillar hatches
from an egg and
eats leaves to grow.

A butterfly emerges
from the pupa with
soft and folded wings.

FIGURE 15.15 Complete metamorphosis

Grasshoppers undergo incomplete metamorphosis, where the insect
undergoes a few stages of ecdysis before becoming an adult. Figure 15.16
shows incomplete metamorphosis.

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•	 The growth rate is low
because it involves little
cell division and cell
elongation.

•	 It is the phase of
adjustment to new
sources available in the
environment.

LAG PHASE

•	 Highest growth rate.

•	 Cell division and
elongation occurs
actively.

•	 Organism’s size
increases rapidly.

EXPONENTIAL PHASE

•	 Organism reaches maturity.

•	 Zero growth rate.

•	 The rate of cell division is similar to the rate of cell death.

•	 Cell division only happens to replace impaired or dead
tissues.

MATURITY PHASE

•	 Negative growth rate.

•	 Organism goes through ageing.

SENESCENCE PHASE

Ageing, illness, lack of nutrients or space eventually leads to
death of an organism.

DEATH PHASE

FIGURE 15.17 Sigmoid growth curve

Lag Phase
Exponential

Phase
Stationary

Phase
Senescence

Phase
Death
Phase

time

gr
ow

th

Maturation
Phase

15.7.4

Growth phases in sigmoid growth curves
of humans and animals
The growth curve is achieved by plotting growth parameters against
time (Figure 15.17). Most organisms’ growth curves show a similar
pattern that is a sigmoid curve (S-shaped). Growth occurs gradually
and continuously. There are six phases in the sigmoid growth curve,
which are the lag phase, exponential phase, stationary phase, maturity
phase, senescence and death phase.

STATIONARY PHASE

•	 Growth rate slows
down and occurs at a
constant rate.

•	 Cells reach maximum
size.

•	 Cells undergo
differentiation to form
specialised cells.

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•	 The process of ecdysis
happens periodically. Polar
growth is not continuous
and is intermittent
(Figure 15.18).

•	 The horizontal part of the
graph indicates zero growth.
At this stage, known as
instar, the insect is not
increasing in length.

•	 The vertical lines of the
graph represent rapid
growth.

•	 At this stage, the nymph
undergoes ecdysis and its
size increases rapidly

•	 Ecdysis occurs multiple
times until the insect
reaches adulthood.

•	 A new exoskeleton forms underneath the old exoskeleton

•	  Before the new exoskeleton hardens, the insect will increase
its volume by sucking in air to expand its body

•	  This action breaks the old exoskeleton and the insect with its
new exoskeleton will emerge

•	  The insect will expand its body one more time before the new
exoskeleton hardens

HOW DOES ECDYSIS HAPPEN?

15.7.5

Intermittent growth curve of animals with
exoskeletons
Insects such as grasshoppers have an exoskeleton made up of chitin.
The exoskeleton does not grow proportionately with the growth of the
insect. To allow growth and development, animals with exoskeletons
must shed their hard exterior.
The moulting process of the exoskeleton that allows growth and
development of insects is called ecdysis. This process is controlled by
hormones.

ICT 15.2

Video: Insect ecdysis
(Accessed on 21 August

2019)

The stages between ecdysis are called instar and at this stage, the insect
is known as a nymph. During instar, the insect is actively building tissue
and increasing body volume.

time (day)

body length (cm)

egg
ecdysis

ecdysis

ecdysis

adult

instar IV

instar V

instar III

instar I

instar II

FIGURE 15.18 Growth curve of animals with exoskeletons

ecdysis

ecdysis

PHOTOGRAPH 15.5
A cicada emerging from its
old exoskeleton

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Reproductive
System	of
Humans

Gametogenesis Development	of
Human	Foetus

Formation	of	Twins

Health	Issues	Related
to	the	Human

Reproductive	System

Growth	in
Humans	and
Animals

Menstrual
Cycle

SEXUAL REPRODUCTION, DEVELOPMENT AND GROWTH IN HUMANS AND ANIMALS

•	Male
reproductive
system

•	Female
reproductive
system

•	Spermatogenesis
and	oogenesis

•	Gamete	structure:
sperm	and
secondary	oocyte

•	Comparison
between
spermatogenesis
and	oogenesis

•	Fertilisation
process	and
the	formation	of
zygotes

•	Role	of	placenta
and	umbilical	cord
in	the	development
of	a	foetus

•	Necessity	for
separate	foetal
and	maternal
blood	circulatory
systems

•	 Identical	twins
•	Fraternal	twins
•	Conjoined	twins

Causes	of	human
impotency

•	Growth	of	insects
with	exoskeleton:

–			complete
metamorphosis

–			incomplete
metamorphosis

•	Sigmoid	growth
curves	of	humans	and
animals

•	 Intermittent	growth
curve	of	animals	with
exoskeletons

•	Changes	in	the	levels	of
hormones	during:
–		menstruation
–		follicle	development
–		thickening	of	the	endometrium
–		ovulation
–		corpus	luteum	formation

•	Changes	in	the	levels	of
hormones	during:
–		pregnancy
–		miscarriage

•	Premenstrual	syndrome	and
menopausal	syndrome

Summary

1 Describe how to measure growth
in animals.

2 Explain the differences between complete
and incomplete metamorphosis.

15.7Formative Practice

3 Explain the event that happens during the
exponential phase.

4 Why must insects go through ecdysis?

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Have you mastered the following important concepts?
•	 Male and female reproductive systems
•	 Spermatogenesis and oogenesis
•	 Gamete structure
•	 Changes in hormone level, follicle growth, endometrial thickening, ovulation and

corpus luteum formation within the menstrual cycle
•	 Changes in hormone level in a pregnancy and a miscarriage
•	 Premenstrual syndrome and menopause
•	 Fertilisation process until the formation of zygote
•	 Early embryo development until implantation
•	 Role of human chorionic gonadotropin (HCG) hormone during early pregnancy
•	 Fetal and maternal blood circulation
•	 Formation of twins (identical, fraternal, conjoined)
•	 Health issues related to the human reproductive system
•	 Sigmoid growth curve of humans and animals
•	 Growth of insects (complete and incomplete metamorphosis)

1 What causes the premenstrual syndrome in some women?

2 State the differences between the formation of identical and fraternal twins.

3 The foetus has its own blood circulation system, separate from its mother.
Explain why.

4 (a)  A pair of identical twins were separated at birth. Once they reached adulthood,
they found out that they both have different body sizes. Explain the factors that
would cause this.

(b) Explain why pregnant mothers must stop smoking.

Self Reflection

Summative Practice 15

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5 State the changes that occur to a zygote from fertilisation up to birth.

6 A woman took contraceptive pills to prevent pregnancy. The pill inhibits secretions of the
Follicle Stimulating Hormone (FSH) from the pituitary gland. Explain the effects of taking
contraceptive pills on the menstrual cycle.

7 Figure 1 shows the hormonal regulation of a menstrual cycle.

hormone X hormone Y

hormone P hormone Q
ovulation

structure T

primary
follicle

hormone
level

days0 2 4 6 8 10 12 14 16 18 20 22 24 26 28

pituitary gland

FIGURE 1

(a) State the effect on ovum development if hormone X is not enough.

(b) Explain the effects of hormone P and hormone Y imbalance.

(c) Based on Figure 1, describe the relationship between changes in structure T with the
level of hormone P and hormone Q.

(i) from day 16 to day 24

(ii) from day 24 to day 28

8 Figure 2 shows a human foetus inside a
uterus.

(a) Name the structures labelled P and Q.

(b) Explain the blood composition that
flows through the blood vessel at Q.

(c) Explain the function of structure P.

(d) (i)  State the types of immunity a foetus
can inherit from its mother.

(ii)  Explain how structure P helps in
foetal immune response.

FIGURE 2

P
Q

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Essay Questions

9 A woman having problems getting pregnant needed an injection of hormone X from a
specialist. Hormone X has the same function as the luteinizing hormone (LH). After a
certain period, the woman was pregnant.
Explain how the hormone X injection can help  the woman to get pregnant.

10 (a)  Describe the process of sperm production in
the testes.

(b) Figure 3 shows the formation of two sets
of twins. Compare the formation of the
twins R and S.

Enrichment

11 During ejaculation, approximately 300 million sperms
are released. From this amount, only about 300 sperms
arrive at the secondary oocyte, and only one will be
successful in fertilising the ovum. If only one sperm
reaches the secondary oocyte, fertilisation will not take
place. Explain why.

12 Describe how changes in different hormone levels in one menstrual cycle prepare a woman
for pregnancy.

13 The umbilical cord is the lifeline between the foetus and its mother. Cord blood is blood
left in the umbilical cord and placenta after birth. After a baby is born, cord blood is kept
as it is a source of stem cells rich in hematopoietic stem cells. Is it important for parents
to keep the cord blood for their children’s future?

FIGURE 3
R S

Complete answers are
available by scanning the
QR code provided

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Active transport—The movement of
substances across the membrane of living
cells, against the concentration gradient
with the help of carrier proteins and energy
from ATP.

aerobic respiration—The complete oxidation
of glucose to carbon dioxide, water and
energy by using oxygen.

anabolism—The metabolic process that
synthesises complex molecules from
simpler molecules. The process requires
energy.

anaerobic respiration—The incomplete
oxidation of glucose without the use of
oxygen or in limited oxygen supply.

appendicular skeleton—The part of the
skeleton that consists of the pectoral and
pelvic girdle, leg bones and arm bones.

axial skeleton—The part of the skeleton that
consists of the skull, vertebral column,
sternum and rib cage. Forms the main axis
of the body.

Balanced nutrition—Food nutrition that
contains all nutrients in the right amount to
fulfill the requirements of the body.

biohazard—Any chemical or biological agent
that poses a threat or risk to humans and the
environment.

blastocyst—The early developmental stage
of mammalian embrio that consists of a ball
of cells with a hollowed centre that is filled
with fluid.

bolus—The ball of chewed food that has been
mixed with saliva, formed in the mouth
through the action of the tongue before
being swallowed.

Carbaminohemoglobin—A compound that
consists of carbon dioxide and the pigment
haemoglobin in the blood.

catabolism—The metabolic pathway that
breaks down complex molecules into simpler
molecules. The process releases energy.

crenation—The shrunken state of animal
cells when the surrounding solution is
hypertonic towards the cytoplasm of
the cells.

Deamination—The removal of an amino
group from an amino acid.

dendrite—The nerve fibre that receives
impulses from adjacent neurons and
transmits them towards the cell body.

deoxyribonucleic acid (DNA)—Nucleic acid
that carries the genetic codes of an
organism and is the main component of
chromosomes.

diploid—Describes two sets of chromosomes,
one set from the male parent and another
set from the female parent.

Effector—Parts of the body that receive
instructions from the control centre and
respond to the stimuli accordingly.

embryo—The early developmental stage of
zygote in seeds (in plants), eggs (in animals),
or uterus (in humans and animals).

emphysema—A condition where the air sacs in
the lungs are damaged and cause difficulties
in breathing.

enzyme—The organic catalyst, normally
proteins, that catalyse biochemical reactions
in living cells.

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Gametogenesis—The process of male
and female gametes formation in the
reproductive organ.

Golgi apparatus—A cellular component in
the cytoplasm that processes, packs, and
distributes secretory substances such as
enzymes and proteins.

Graafian follicle—Mature follicle in the
ovary that contains secondary oocyte and
produces the hormone oestrogen.

Haemoglobin—Protein in the red blood cell
that functions to transport oxygen.

haemophilia—Blood disease that causes the
patient’s blood clotting to be impaired due to
the lack of clotting factors.

homeostasis—The regulation of the
internal environment of organisms so that
physiological processes can proceed at the
optimum level.

hormone—Chemical substances that regulate
specific functions in the body.

Immunity—The body’s ability to fight infectious
diseases carried by pathogens.

implantation—The adhering of the embryo (at
the blastocyst stage) to the wall of the uterus.

insulin—Hormone that stimulates the
conversion of glucose to glycogen in the liver
and muscle cells.

Ligament—Elastic tissues that connect bone
to bone.

lysosome—Membrane-bound sacs that
contain enzymes that digest substances in
the food vacuole.

Meiosis—The cell nucleus division that
produces four haploid daughter cells.

mitosis—The cellular division that produces two
daughter cells that contain a similar number
and type of chromosome as the parent cell.

morula—A solid ball of cells during the
development of embryo before the
blastocyst stage.

Nephron—The functional unit in the kidney that
consists of the glomerulus, Bowman capsule,
convoluted tubule, Henle loop and
collecting duct.

neuron—Cells in the nervous system that
consists of the axon, cell body and dendrites.

nucleic acid—A complex organic compound in
living cells that consists of nucleotide chains.
There are two types of nucleic acid, which
are DNA and RNA.

nucleotide—The basic unit of DNA molecule
that contains phosphate group, ribose or
deoxyribose, and a nitrogenous base.

nucleus—The largest cellular component in
the cell that contains genetic materials. The
nucleus acts as the control centre for the cell.

Oogenesis—The formation of the ovum in the
ovary.

organism—Living things that are capable of
conducting living processes such as feeding,
growing, reproducing and breathing.

osmosis—The diffusion of water molecules
from a region of higher water potential
towards a region of lower water potential,
across a selectively permeable membrane.

oxyhaemoglobin—A compound that is formed
when oxygen combines with haemoglobin in
erythrocytes.

312

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Pathogen—The microorganisms that carry
infections and diseases.

phloem—The vascular tissue that is involved in
the transport of food materials from the
site of photosynthesis to other parts that
need them.

placenta—The organ that forms from the tissue
of the foetus and the mother to allow for
material exchanges between the foetus
and the mother.

plasmolysis—The shrinking of cytoplasm
from the plant cell wall as a result of water
loss through osmosis.

platelet—Fragments of cell cytoplasm in
the blood that contain no nucleus and are
involved in blood clotting.

Receptor—Specialised sensory cells that
detect stimuli.

reflex arc—The stimulus pathway that triggers
reflex responses. The pathway consists of
receptors, control centres and effectors.

Sacrum—The triangular bone in the hip area of
the vertebral column.

skeletal muscle—Muscles that connect a
bone to another bone. The movement of
the skeleton relies on the contraction of
skeletal muscles.

smooth muscle—Non-striated muscles
that can be found in intestinal walls and
blood vessels.

spermatogenesis—The formation of sperm in
the testis.

sternum—The bone in the middle section of the
vertebrate chest.

synapse—A site between two nerve cells, or
neurons and effector to communicate.

Telophase—The final stage in cell division,
when the nuclear membrane envelopes the
nucleus of each daughter cell.

tendon—Flexible non-elastic tissue that joins
the muscle to the bone.

Ultrafiltration—The filtration process of blood
plasma that contains dissolved nutrients,
across the wall of blood capillary.

Vacuole—Sacs that contain cell sap that can
be found in the cytoplasm.

vertebra—Small bones that form the spine

Zygote—The union of the ovum (female
gamete) and sperm cell (male gamete) during
fertilisation.

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314

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