JK-TK/Newdata huggingface dataset:
Oestrogen brings about the repair and healing of the inner lining of the uterus (endometrium) which had been destroyed during menstruation. Oestrogen level stimulates the pituitary gland to produce (Luteinising Hormone (L.H). This hormone makes the mature Graafian follicle to release the ovum into the funnel of oviduct, a process called ovulation. After releasing the ovum, the Graafian follicle changes into a yellow body called corpus luteum. The luteinising hormone stimulates the corpus luteum to secrete a hormone called progesterone which stimulates the thickening and vascularisation of endometrium. This prepares the uterine wall for implantation of the blastocyst. If fertilisation takes place, the level of progesterone increases and thus inhibits FSH from stimulating the maturation of another Graafian follicle. If fertilisation does not occur, the corpus luteum disintegrates and the level of progesterone goes down. The endometrium, sloughs off and menstruation occurs. Advantages of Reproduction Asexual
Good qualities from parents are retained in the offspring without variation. New individuals produced asexually mature faster. Process does not depend on external factors which may fail such as pollination. New individuals obtain nourishment from parent and so are able to survive temporarily under unsuitable conditions. No indiscriminate spreading of individuals which can result in wastage of offspring. Takes a shorter time and leads to rapid colonization. Disadvantages of asexual reproduction
New offspring may carry undesirable qualities from parents. Offspring may be unable to withstand changing environmental conditions. Faster maturity can cause overcrowding and stiff competition. Reduced strength and vigour of successive generations. Advantages of sexual reproduction
Leads to variations. Variations which are desirable often show hybrid vigour. High adaptability of individuals to changing environmental conditions. Variations provide a basis for evolutionary changes. Disadvantages of sexual reproduction
Fusion is difficult if two individuals are isolated. Some variations may have undesirable qualities. Population growth is slow. Practical Activities
Examining the stages of mitosis
About 2 mm of a root tip of onion bulb is cut off and placed on a microscope slide. A stain e.g. aceto-orcein is added and the root tip macerated using a scapel. A cover slip is added and observations made. Different stages of mitosis can be observed.
aceto-orcein is added and the root tip macerated using a scapel. A cover slip is added and observations made. Different stages of mitosis can be observed. Examining the stages of meiosis
An unopened bud of Tradescantia is obtained
The anther is removed and placed on a microscope slide. A few drops of hydrochloric acid and acetic-orcein stain are added. A cover slip is placed on the anther. Pressing the cover slip gives a thin squash, which is observed under the microscope. Different stages of meiosis are observed. To observe the structure of Rhizopus
Rhizopus grow on moist bread left under suitable temperature
A piece of moist bread is placed on a petri-dish or enclosed in a plastic bag and observe daily for four days. Under a low power microscope the sporangia and stolons can be observed. To examine spores on sori of ferns
Obtain the fern plant. Detach a frond from the plant and observe the under-side using a hand lens to see the raised brown patches - the sori. Open up the sorus to observe the sporangia. Examine insect and wind pollinated flowers
Obtain insect pollinated flowers e.g. crotalaria, hibiscus/Ipomea, Solanum, incunum. Note the scent, colour and nectar guides. A description of the calyx, corolla, androecium and gynoecium is made. Obtain a wmd pollinated flower e.g,' maize, star-grass, sugar-cane, Kikuyu grass. Observe the glumes, spikes and spikelet. Examine a single floret, and identify the androecium and gynoecium. Classifying fruits
Obtain different fruits - oranges, mangoes, maize, castor oil, bean pod, black jack . Observe the fruits, classify them into succulent, dry-dehiscent or indehiscent. Dissection of Fruits
Obtain an orange and a mango fruit. Make a transverse section. Observe the cut surface and draw and label the parts. Note that the fruit is differentiated into epicarp, mesocarp and endocarp. Obtain a pod of a legume. Open up the pod and observe the exposed surface. Draw and label the parts. Note that the fruit wall is not differentiated.
Open up the pod and observe the exposed surface. Draw and label the parts. Note that the fruit wall is not differentiated. Dispersal of fruits and seeds
Obtain animal dispersal fruits, like oranges, tomatoes, black jack, sodom apple. Identify the way by which each is adapted to dispersal by animals. Obtain wind dispersed fruit/seed
e.g. Nandi flame, Jacaranda Sonchus, cotton seed, Tecoma. END
GROWTH AND DEVELOPMENT
Concept of Growth and Development
Growth is a characteristic feature of all living organisms. Most multicellular organisms start life as a single cell and gradually grow into complex organisms with many cells. This involves multiplication of cells through the process of cell division. This quantitative permanent increase in size of an organism is referred to as growth. For growth to take place the following aspects occur
Cells of organisms assimilate nutrients hence increase in mass. Cell division (mitosis) that lead to increase in the number of cells. Cell expansion that leads to enlargement an increase in the volume and size of the organism. It is therefore possible to measure growth using such parameters as mass, volume, length, height, surface area. On the other hand development is the qualitative aspect of growth which involves differentiation of cells and formation of various tissues in the body of the organism in order for tissues to be able to perform special functions. It is not possible to measure ac aspects of development quantitative. Therefore development can be assessed terms of increase in complexity of organism e.g. development of leaves, flowers and roots. A mature human being has millions of cells in the body yet he or she started from; single cell, that is, a fertilised egg. During sexual reproduction mammals an ovum fuses with a sperm form a zygote. The zygote divides rapidly without increasing in size, first into 2, 4, 8, 16,32, 64 and so on, till it forms a mass cells called morula. These first cell division is called cleavages. The morula develops a hollow part, resulting into a structure known as a blastula (blastocyst). Later, blastocyst cells differentiate into an inner layer (endoderm) and the outer layer (ectoderm). The two-layered embryo implants into the uterine wall and, by obtaining nutrients from the maternal blood, starts to grow and develop.
The morula develops a hollow part, resulting into a structure known as a blastula (blastocyst). Later, blastocyst cells differentiate into an inner layer (endoderm) and the outer layer (ectoderm). The two-layered embryo implants into the uterine wall and, by obtaining nutrients from the maternal blood, starts to grow and develop. BlastocoeJ
Fertilised egg 2-celled stage 4-celled stage
{zygote) Morula Blastula
(mass of cells)
As the embryo grows and develops, changes occur in cell sizes and cell -types. Such changes are referred to as growth and development respectively. These processes lead to morphological and physiological changes in the developing young
organism resulting into an adult that is more complex and efficient. In the early stages, all the cells of the embryo look alike, but as the development process
continues the cells begin to differentiate and become specialised into different tissues to
perform different functions. Growth involves the synthesis of new material and protoplasm. This requires a continuous supply of food, oxygen, water, warmth and means of removing
waste products. In animals, growth takes place all over the body but the rates differ in the various parts of the body and at different times. In plants however, growth and cell division mostly take place at the root tip just behind the root cap and stem apex. This is referred to as apical growth which leads to the lengthening of the plant. However, plants do not only grow upwards and downwards but sideways as well. This growth leads to an increase in width (girth) by the activity of cambium cells. The increase in girth is termed as secondary growth. Study Question 1-State two major differences between growth and development
Measurement of growth
Growth can be estimated by measuring some aspect of the organism such as height, weight, volume and length over a specified period of time. The measurements so obtained if plotted against time result into a growth curve. Study Question 2
The following results were obtained from a study of germination and early growth of maize. The grains were sown in soil in a greenhouse and.at two-day intervals. Samples were taken, oven dried and weighed. See table . Table
Plot a graph of dry mass of embryo against time after sowing. Describe the shape of the graph. For most organisms when the measurements are plotted they give an S-shaped graph called a sigmoid curve such as in figure .
Table
Plot a graph of dry mass of embryo against time after sowing. Describe the shape of the graph. For most organisms when the measurements are plotted they give an S-shaped graph called a sigmoid curve such as in figure . Time
Fig. 4.2: TSie sigmoid growth curve
This pattern is due to the fact that growth tends to be slow at first and then speeds up
and finally slows down as adult size is reached. A sigmoid curve may therefore be divided into four parts. Lag phase (slow growth)
This is the initial phase during which little growth occurs. The growth rate is slow due to various factors namely:
(i) The number of cells dividing are few. (ii) The cells have not yet adjusted to the surrounding environmental factors. Exponential phase (log phase)
This is the second phase during which growth is rapid or proceeds exponentially. During this phase the rate of growth is at its maximum and at any point, the rate of growth is proportional to the amount of material or numbers of cells of the organism already present. This rapid growth is due to:
(i) An increase in number of cells dividing,2-4-8-16-32-64 following a geometric progression,
(ii) Cells having adjusted to the new environment,
(iii) Food and other factors are not limiting hence cells are not competing for resources,
(iv) The rate of cell increase being higher than the rate of cell death. Decelerating Phase
This is the third phase during which time growth becomes limited as a result of the effect of some internal or external factors, or the interaction of both. The slow growth is due to: (
i) The fact that most cells are fully differentiated. (ii) Fewer ceils still dividing,
(iii) Environmental factors (external and internal) such as:
shortage of oxygen and nutrients due to high demand by the increased number of cells. space is limited due to high number of cells. accumulation of metabolic waste products inhibits growth. limited acquisition of carbon (IV) oxide as in the case of plants. Plateau (stationary) phase
This is the phase which marks the period where overall growth has ceased and the
parameters under consideration remain constant. This is due to the fact that:
The rate of cell division equals the rate of cell death. Nearly all cells and tissues are fully differentiated, therefore there is no further increase in the number of cells. The nature of the curve during this phase may vary depending on the nature of the parameter, the species and the interns!
This is due to the fact that:
The rate of cell division equals the rate of cell death. Nearly all cells and tissues are fully differentiated, therefore there is no further increase in the number of cells. The nature of the curve during this phase may vary depending on the nature of the parameter, the species and the interns! factors. In some cases, the curve continue to increase slightly until organism dies as is the case monocotyledonous plants, man invertebrates, fish and certain reptiles. indicates positive growth. In some ot cases the curve flattens out indicating change in growth while other growth curv may tail off indicating a period of negat growth rate. This negative pattern characteristic of many mammals includi humans and is a sign of physical senesee associated with increasing age. Study Question 3
What happens during the following; log and stationary phases of growth? However, the sigmoid curve does not to all organisms, for example, arthropods. I insects, growth takes place at intervals-volume changes are plotted against time., different curve is obtained. This is cal intermittent growth curve. See figure 43,
The intermittent growth in insects is due to the fact that they have an exoskeleton and hence growth is possible only when it is shed. This shedding process is known as moulting or ecdysis. However, cell division continues to take place during the inter-moult phase but the expansion of tissues is limited by the unshed exoskeleton. Practical Activity I: Project
To measure the growth of a plant
Requirements
Small plots/boxes, meter rule and seeds of beans (or green grams, peas, maize),
Procedure
. Place some soil in the box or prepare a small plot outside the laboratory. Plant some seeds in the box and place it in a suitable place outside the laboratory (or plant the
seeds in your plot). Water the seeds daily. Observe the box/plot daily and note the day the seedlings emerge out of the soil. .Measure the height of the shoot from the soil level up to the tip of the shoot. Repeat this with four other seedlings. Work out the average height of the shoots for this day. Repeat procedure 5 every three days for at least three weeks. Record the results in a table form. On the same seedlings measure the length of one leaf from each of the fiveseedlings (from leaf apex to itsattachment on the stem). Calculate the average length of the leaves and record in the table.
Record the results in a table form. On the same seedlings measure the length of one leaf from each of the fiveseedlings (from leaf apex to itsattachment on the stem). Calculate the average length of the leaves and record in the table. Plot a graph of the height of the shoot against time. On the same axes plotlength of leaf against time. Compare the two graphs drawn. 4.2 Growth and Development in Plants
The main growth and development phase in plants begins with the germination of the mature seed. Seeds are of two kinds depending on the number of cotyledons or embryo leaves. Practical Activity 2
To investigate structural differences between monocotyledonous and dicotyledonous seeds
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£4.0 qa
3 3.5
3.0
2.5
2.0
1.5
Adult
moulting
2ndinstar>/^grawth phase
^^tf^_/ jntermoult phaseji—i—i—i—ii—l__
246 8101214161820222426283032343638404244
Time in days Fig. 4.3: Growth curve showing increase in length of the short homed grasshopper
Requirements
Bean seeds and maize grains which have been soaked overnight. Scalpel or razor blades, iodine solution, Petri-dish and hand lens. Procedure
Using a scalpel or razor blade make longitudinal sections (LS) of both the bean seed and the maize grain. Observe the LS of the specimens using a hand lens. Note any structural difference between the specimens. Draw the LS of each specimen and label. Puta drop of iodine solution on the cut surfaces of both specimens. Note any differences in colouration with iodine on the surfaces of the two specimens. On your diagrams indicate the distribution of the stain. Account for the difference in distribution of the colouration with iodine in the two specimens. Structure of the Seed
A typical seed consists of a seed coat enclosing an embryo. The seed coat is the outer covering which, in most seeds, is made
-Remains of style
Position of plumule
Position of radicle Scutellum
Attachment to External Parent plant
Position of radicle
Micropyle Hilum
Testa
Structure of monocotyledonous seed (maize grain)
External (bj Structure of dicotyledonous seed
Fig.
Account for the difference in distribution of the colouration with iodine in the two specimens. Structure of the Seed
A typical seed consists of a seed coat enclosing an embryo. The seed coat is the outer covering which, in most seeds, is made
-Remains of style
Position of plumule
Position of radicle Scutellum
Attachment to External Parent plant
Position of radicle
Micropyle Hilum
Testa
Structure of monocotyledonous seed (maize grain)
External (bj Structure of dicotyledonous seed
Fig. 4.4: Structure of seeds
up of the two layers, an outer testa and inner one, the legmen. The testa is thick; the tegmen is a transparent membrane tissue. The two layers protect the seed bacteria, fungi and other organisms whk may damage it. There is a scar called hilurn on one part of the seed. This is point where the seed had been attached the seed stalk or funicle. Near one end of 1 hilum is a tiny pore, the micropyle. This allows water and air into the embryo, embryo is made up of one or two seed leavi or cotyledons, a plumule (embryonic sh( and a radicle (the embryonic root). The of the radicle is opposite the micropyle. In some seeds the cotyledons swollen as they contain stored food for growing plumule and radicle. Such seeds, called non-endospermic seeds. In ot cases, the seeds have their food stored in: endosperm. Such seeds are call endospermic seeds. Seeds with one cotyk are referred to as monocotyledonous wi those with two are referred to dicotyledonous. This is the major basis i differentiation between the two large cb of plants, the monocotyledonae aa dicotyledonae. Scutellum
Cotyledon
Coieoptile
Plumule
Radicle
Coleorhiza
Internal
Plumule
Radicle
Cotyledon
Internal
Fused pericaT and testa
Dormancy in Seeds
The embiyo of a dry, fully developed seed usually passes through a period of rest after ripening period. During this time the seed performs all its life (physiological) processes very slowly and uses up little food. This is a period of dormancy.
Scutellum
Cotyledon
Coieoptile
Plumule
Radicle
Coleorhiza
Internal
Plumule
Radicle
Cotyledon
Internal
Fused pericaT and testa
Dormancy in Seeds
The embiyo of a dry, fully developed seed usually passes through a period of rest after ripening period. During this time the seed performs all its life (physiological) processes very slowly and uses up little food. This is a period of dormancy. Even if all the favourable environmental conditions for germination are provided to the seed during this period of dormancy, the seed will not germinate. This is due to the fact that the seed embryo may need to undergo further development before germination. Some seeds can germinate immediately after being_shed from the parent plant (e.g. most tropical plants) while others must pass through dormancy period, lasting for weeks, months or even years before the seed can germinate. Dormancy provides the seeds with enough time for dispersal so that they can germinate in a suitable environment. It also enables seeds to survive during adverse environmental conditions without depleting their food reserves. The embryo has time to develop until favourable conditions are available e.g. availability of water. Factors that Cause Dormancy
Embryo may not yet be fully developed. Presence of chemical inhibitors that inhibit germination in seeds e.g.abscisic acid. Very low concentrations of hormones e.g. gibberellins and enzymes reduces the ability of seeds to germinate. Hard and impermeable seed coats prevent entry of air and water in some seeds e.g. wattle. In some seeds the absence of certain wavelengths of light make them remain dormant e.g. in some lettuce plants. Freezing of seeds during winter lowers their enzymatic activities rendering them dormant. Ways of Breaking Dormancy
When the seed embryos are mature then the seed embryos can break dormancyand germinate. Increase in concentration of hormones e.g. cytokinins and gibberellins stimulate germination. Favourable environmental factors such as water, oxygen and suitable temperature. Some wavelengths of light trigger the production of hormones like gibberellins leading to breaking of dormancy. Scarification i.e. weakening of the testa is needed before seeds with hard impermeable seed coats can germinate. This is achieved naturally by saprophytic bacteria and fungi or by passing through the gut of animals.
Scarification i.e. weakening of the testa is needed before seeds with hard impermeable seed coats can germinate. This is achieved naturally by saprophytic bacteria and fungi or by passing through the gut of animals. In agriculture the seeds of some plants are weakened by boiling, roasting and cracking e.g. wattle. Seed Germination
The process by which the seed develops into a seedling is known as germination. It refers to all the changes that take place when a seed becomes a seedling. At the beginning of germination water is absorbed into the seed through the micropyle in a process known as imbibition and causes the seed to swell. The cells of the cotyledons become turgid and active. They begin to make use of the water to dissolve and break down the food substances stored in the cotyledons. The soluble food is transported to the growing plumule and radicle. The plumule grows into a shoot while the radicle grows into a root. The radical emerges from the seed through micropyle, bursting the seed coat as it does so. Conditions Necessary for Germination
Seeds can easily be destroyed by unfavourable conditions such as excessive heat, cold or animals. Seeds need certain conditions to germinate and grow. Some of these conditions are external, for example water, oxygen and suitable temperature while others are internal such as enzymes, hormones and viability of the seeds themselves. Water
A non-germinating seed contains very little water. Without water a seed cannot germinate. Water activates the enzymes and provides the medium for enzymes to act and break down the stored food into soluble form. Water hydrolyses and dissolves the food materials and is also the medium of transport of dissolved food substances through the various cells to the growing region of the radical and plumule. Besides, water softens the seed coat which can subsequently burst and facilitate the emergence of the radicle. Oxygen
Germinating seeds require energy for cell division and growth. This energy is obtained from the oxidation of food substances stored in the seed through respiration thus making oxygen an important factor in seed germination. Seed in water logged soil or seed buried deep into the soil will not germinate due to lack of oxygen. Temperature
Most seeds require suitable temperature before they can germinate. Seeds will not germinate below 0°C or above 47° C. The optimum temperature for seeds to germinate is 30°C.