Biology Spec points covered Starter options Practical activity Teacher-led activity CB4a Evidence for Human Evolution B4.4 B4.5 Describe the evidence for Human evolution, based on fossils, including: a Ardi from 4.4 million years ago b Lucy from 3.2 million years ago c Leakey’s discovery of fossils from 1.6 million years ago. Describe the evidence for Human evolution based on stone tools, including: a the development of stone tools over time b how these can be dated from their environment. 1) Ask students to think about how humans or other animals might evolve in the future. They could draw a labelled picture to show how humans might change and give a reason why they might evolve in that way. 2) Ask students to jot down what evidence we have for identifying how our ancestors lived in the following periods: 100 years ago, 1000 years ago and 100 000 years ago. Take examples of each and consider the reliability of the different kinds of evidence. Establish the idea that this leads to an incomplete record that scientists are still trying to fill in. Challenge students to find out more about human evolution. Ensure that students understand that the huge timescales involved in human evolution mean that the fossil record is full of gaps. It is for this reason that scientists cannot agree on an evolutionary tree for human evolution and various educated guesses need to be made to fill in the gaps. Genetic analysis is helping with the research but due to the degradation of DNA with time this is not a complete answer to the problems of piecing together human evolution. Digital: Ideas about human evolution video CB4b Darwin’s theory B4.2 Explain Darwin’s theory of evolution by natural selection. 1) Ask whether if one person in the class gets a cold, everyone will? Elicit Divide the class into groups. Each group will get some pasta shapes of different colours (in Explain Darwin’s theory of evolution as a series of stages to help
B4.3 Explain how the emergence of resistant organisms supports Darwin’s theory of evolution including antibiotic resistance in bacteria. the idea that not everyone gets ill. Challenge students to explain why not everyone gets the cold and introduce the idea that this is partly due to inherited variation – some people are naturally immune to some colds/diseases. 2) Sketch a normal distribution curve on the board and tell students that it shows variation in beak length in a population of sandpipers. The birds dig with their beaks to find small animals to eat. Ask students to suggest why there are more birds with the middle beak length and very few with either very short or very long beaks. Elicit the idea that conditions in the environment make it easiest for birds with approximately equal amounts, including green pasta), which are models for insects. They design a table in which to record the numbers of each different colour of pasta shape. The shapes are then spread out in an open, grassy area. One student is ‘the bird’ and is given a pair of tongs/forceps. The student has 2 minutes to pick up as many pasta shapes as possible. Students count the numbers of each colour returned and calculate percentages. Students should find that red, orange and yellow pasta pieces are more readily found than green pieces, although this will be slightly dependent on the colour of the grass at the time of doing the investigation. Students repeat their experiment to improve the repeatability of the data. Students then calculate mean percentages returned for each colour. They then use this data to draw pie charts. Ask them to speculate on the students remember what happens. Students should, though, be aware that the process is continuous. Correct misconceptions as they arise. The most common ones revolve around the idea that the environment directly causes organisms to change. It is worth dwelling on the first ‘stage’ of evolution to ensure that students realise that genetic variation is ever present and that natural selection cannot work if there is no genetic variation to start with. Digital: Evolution of antibiotic resistence presentation
medium beak lengths to survive best: future evolution of this green species if: a) the grass remains green b) the grass turns yellow. Equipment: packets of differently coloured pasta, must contain green pasta pieces as well as other colours (500 g per 4–5 students) (you could use buttons of different colours instead but these are not biodegradable), forceps or tongs, stop watch, pot to collect pasta shapes in, area of grass CB4c Classification B4.7 Describe how genetic analysis has led to the suggestion of the three domains rather than the five kingdoms classification method 1) Ask students to suggest how a visitor to the area might be able to find an individual student in a school. Give groups of students 5 minutes to come up with a plan of how the visitor would do this. The groups for a student might be: school > year group > form > workgroup > individual. 2) Show students a Ask students to sort themselves into two groups and then think of another way of dividing themselves into two or more groups. This process can be repeated a number of times. Ask students to explain their reasoning behind their classification systems each time and suggest which system was the best and why. Elicit the idea that scientists group organisms into large groups based on differences Take students through the classification of several plants and animals, showing how the number of organisms in each group gets smaller and smaller and how the similarities between the organisms increase. Ask students to suggest other members of the groups as you work through the
natural bath sponge (or image of one). Introduce the idea that the sponge is what remains of the insides of an organism. Ask students if they think it’s a plant or an animal or neither. Ask students to list some features that they would find out more about, in order to be certain whether it was a plant or an animal or whether it belonged to some other kingdom (fungi, protists, bacteria). between the characteristics, and these groups are called kingdoms. classifications. Ensure that students understand that the closer a group is to the genus or species grouping, the more closely related the organisms will be and the more similar their DNA will be. Point out that in the past scientists looked at the characteristics that they could see, but today classification is usually done according to how similar the DNA is. Digital: Classification of kingdoms and domains presentation CB4d Breeds and varieties B4.8 B4.10 Explain selective breeding and its impact on food plants and domesticated animals. Describe genetic engineering as a process which involves modifying the genome of an organism to introduce desirable characteristics. 1) Challenge students to produce a list of useful characteristics for cattle on a UK farm (e.g. good meat, quick growing, produce a lot of milk, docile). Then ask what other characteristics might be useful for cattle being farmed in northern The practical measures the amounts of citric acid in different varieties of the same citrus fruit, which is an important factor for breeders. 1 cm3 of 0.1 mol dm−3 sodium hydroxide will neutralise 0.0064 g of citric acid. If you are using apples the multiplication factor should Detail of some different breeds and varieties of common animals and plants that are farmed for food, and how their characteristics make them suitable for farming in certain locations. Present the characteristics and ask
Scotland (e.g. thick fur) or Africa (thin fur, less requirement for water. Establish the idea that new breeds of animals and plant are produced to be the most use in a certain set of environmental conditions. 2) Woolly sheep have been bred to produce a lot of wool. However their long woolly tails trap faeces and mud and become infested with maggots. So farmers ‘dock’ the tails of sheep. It would be easier to farm woolly sheep that had naturally short tails. Ask students how they would breed woolly sheep with naturally short tails. be 0.067 (for malic acid) or for grapes use 0.075 (for tartaric acid). There should be obvious differences in acidity between different varieties of fruit. Equipment: eye protection, different varieties of the same species of fruit (e.g. oranges, limes), preferably sliced in half, fruit juicer/squeezer, 2 pipettes or syringes or small measuring cylinders, burette, clamp and stand, filter funnel, filter paper, small beaker, conical flask, phenolphthalein indicator, 0.1 ml dm–3 sodium hydroxide solution, distilled water Optional: refractometer, accurate balance (for Brix measurements), knife to cut fruits students why those characteristics are suitable. Digital: Farm breeds and varieties presentation CB4e Genes in agriculture and medicine B4.14 Evaluate the benefits and risks of genetic engineering and selective breeding in modern agriculture and medicine including practical 1) Tell students a plant breeder wishes to produce a new variety of orange. Ask students to come up with a list of Students research and think about the benefits and risks of a range of selectively bred/genetically engineered organisms. Remind students of the overall process of genetic engineering. Use four different colours of individual
higher susceptibility to other diseases. mumps) and some that are non-communicable (e.g. asthma, cancer, diabetes). Ask students to work in pairs to suggest a link between all the words, and then to suggest a way of splitting the words into two groups. while most cancers are not. Then compare the age distribution of people with cancer and with measles. The charts drawn from these will show that the number of cases increases with age for cancer, because it results from the malfunction of cells and the risk of this happening increases with age. However, measles is more common in childhood because once you have had it, you become immune and will not catch it again. with a different virus. Agree that infection with HIV is strongly correlated with infection by cytomegalovirus and Epstein Barr virus. The correlation with human herpesvirus 1 is weaker, and there is a negative correlation (more people without HIV than with) between HIV infection and human herpesvirus 8 infection. Digital: Disease correlations presentation CB5b disease B5.23 B5.24 Describe that many human diseases are caused by the interaction of a number of factors including cardiovascular diseases, many forms of cancer, some lung and liver diseases and diseases influenced by nutrition. Explain the effect of lifestyle factors on non-communicable diseases at local, national 1) Revise KS3: carbohydrates, fats, proteins, vitamins, minerals and fibre. Students jot down, for each group, one example of a food that contains that constituent. Then they describe the main function in the body of each of the main constituents. Introduce deficiency diseases. Students analyse data related to drinking and deaths from alcohol-related conditions. Students will need to know that death from alcohol poisoning is a short-term result of high alcohol intake, whereas liver disease (including cirrhosis) is a result. So it will take many years for the impact of any health campaign on alcohol to show in the statistic of liver disease. Demonstrate the importance of the liver in the breakdown of toxic substances in the following way. Place a small piece of fresh liver in a blender with about twice the volume of water, and blend till smooth. Pour about 1 cm of hydrogen peroxide into a test tube, and explain
treatments for cardiovascular disease including • life-long medication • surgical procedures • lifestyle changes cigarette. Repeat the activity with a lit cigarette in place as shown above. Ask students to describe and, if possible, explain any changes. Emphasise that tobacco smoke contains many substances, and that many are colourless and so not visible. Ask what happens to the substances when the smoke is taken into the lungs. Consider the role of blood in distributing substances around the body. Equipment: for smoking machine: U tube, bung with single hole and bung without hole (for U tube), 2 test tubes, 2 bungs with 2 holes (for test tubes), thermometer, glass or polymer wool, cigarette without filter, universal indicator solution, limewater, glass tubes and connectors, exercise and improving diet. Identify that there are different kinds of cardiovascular disease, such as heart attack (myocardial infarction), stroke, thrombosis, and angina. Students should research the advantages and disadvantages for each kind of treatment, including which kind of patient responds best to that treatment. the proportion of fat in the body, and why too much fat is a problem. Using yourself or a fit student who won't mind the attention, take measurements of heart rate and breathing rate at rest, after two minutes of gentle exercise and after two minutes of moderate exercise. (Remember to allow raised values to return to resting rates before testing again.) Heart rate can be measured at the wrist or by using a digital heart rate monitor. Breathing rate should be measured as the number of breaths taken in 15 seconds. Explain that the heart rate and breathing rate of people who are very unfit and/or obese usually increase more rapidly than those of fitter people. So, the health professional
B5.14 a exposure to pathogen b the antigens trigger an immune response which causes the production of antibodies c the antigens also trigger production of memory lymphocytes d the role of memory lymphocytes in the secondary response to the antigen Explain the body’s response to immunisation using an inactive form of a pathogen. they have had as a child or in school. They should then discuss why they had the vaccinations, what they remember about how they work, and to describe what they felt during and after the vaccination. 2) Ask students to think about the last time they had an infection such as a cold, or flu. They should jot down what they remember about why they caught the infection, what happened during the infection and why it went away. Prompt with the idea that only a few pathogens may enter the body, but that conditions inside the body are good for rapid replication. Lead to the answer that it is only when large numbers of pathogens cause harm or changes in the body, that the impact of the MMR scare. about vaccinations, including those for sexually transmitted diseases such as HPV, hepatitis A and B. Students should prepare questions before the visit. Encourage class discussion of questions to make sure all the key ones are included, such as how vaccinations work, why they produce immunity, why there aren't vaccinations for all diseases. Digital Sexually transmitted infections video
we become aware of illness. CB5h Antibiotics B5.16 B5.20 Explain that antibiotics can only be used to treat bacterial infections because they inhibit cell processes in the bacterium but not the host organism Describe that the process of developing new medicines, including antibiotics, has many stages including discovery, development, preclinical and clinical testing 1) Write the word 'antibiotic' in the middle of the board, then give students a minute or two in pairs or small groups to think of related words or terms. 2) Tell students that a new medicine is being developed to help people suffering from a particular disease. Ask students to work in pairs or small groups to jot down the questions that need answering during the development. Explain to students that many plants contain substances that help protect them against attack by microorganisms. Some of these have been developed into medicines to help treat our diseases. Make sure that students understand that a clear area around a disc indicates where bacteria have been killed. Bacterial lawn plates and plant extracts will need preparing before the lesson. Suitable extracts include: chilli powder, cinnamon, cloves, fennel, garlic, paprika, pepper, thyme. To make an extract, grind 3 g crushed or ground plant material with 10 cm3 ethanol (IDA) and shake vigorously for 10 minutes. Give each group two of the plant extracts to use. Results for all extracts will need to be compared across the class. Clinical trials are a application of the idea of a fair test that students use in their own work. Help students to compare the way they carry out their practical investigations and the way clinical trials by discussing the following aspects: Trial size/ sample size Using controls placebos and 'blind' trials (more able students only) Digital: TBC
CC8b Conservation of mass C1.47 C1.48 C1.49 Explain the law of conservation of mass applied to: a a closed system including a precipitation in a closed flask b a non-enclosed system including a reaction in an open flask that takes in or gives out a gas Calculate masses of reactants and products from balanced equations, given the mass of one substance Calculate the concentration of solutions in g dm-3 1) Show the formation of a yellow precipitate of lead iodide by pouring small amounts of lead nitrate and potassium iodide solutions in a boiling tube. The final mass should be the sum of the two initial masses. Now add dilute hydrochloric acid to marble chips in a boiling tube and ask the students what has happened to the mass. This leads on to gases having mass and the mass decreases because the gas escapes from the open boiling tube. Equipment: 2 x 100 cm3 glass beaker, 2 boiling tubes, boiling tube rack, electronic balance, eye protection, lead nitrate solution (about 40 cm3 of 0.5 mol dm-3), potassium iodide solution (about 40 cm3 of 0.5 mol dm-3), hydrochloric acid (about Students investigate the decomposition of copper carbonate. The expected percentage mass of copper oxide is 64.4% of the mass of copper carbonate used. Students can be asked why their values are different to this and how they can improve the experiment. If their value is lower (most likely), they probably did not heat the tube for long enough. They could improve the experiment by heating the tube again, cooling and re-weighing and repeating this until two mass measurements are the same. This technique is called heating to constant mass. Equipment: For each group: Bunsen burner, heat resistant mat, mineral wool, test tube, test tube holders, a few grams of copper carbonate. Students need access to an electronic balance. Take the students through worked examples one step at a time. Digital Calculating masses of reactants and products presentation
20 cm3 0.5 mol dm-3), 2 g marble chips 2) Revise formulae and balanced equations. Check that students know how to work out the number of atoms of each element in a formula. CC8c Moles C1.52 C1.53 C1.50 C1.51 Explain why, in a reaction, the mass of product formed is controlled by the mass of the reactant which is not in excess Deduce the stoichiometry of a reaction from the masses of the reactants and products Recall that one mole of particles of a substance is defined as: a the Avogadro constant number of particles (6.02 x 1023 atoms, molecules, formulae or ions) of that substance b substance mass of ‘relative particle mass’ g Calculate the number of: 1) When there are large numbers of small items, people usually find the number of them by measuring their mass rather than counting e.g. cashiers in banks check the number of coins in a bag by finding their mass. Have small, sealed jars containing 1 mole of particles of different substances e.g. 18g of water, 12g of carbon, 32g of sulfur, 56g of iron. Explain that these each contain the same number of particles. Ask the students to Students study the reaction between iron and copper sulfate solution The students should find that the correct balanced equation is Fe + CuSO4 → Cu + FeSO4 Equipment: for each group 100 cm3 beaker, evaporating basin, eye protection, filter funnel with filter paper to fit, glass rod, 25 cm3 measuring cylinder, spatula, copper sulfate solution ( 30 cm3 of approximately 0.5 mol dm-3 solution), distilled water, Demonstrate the formation of precipitates of lead iodide by adding different volumes of lead nitrate solution to the same volume of potassium iodide solution and use these to determine the mole ratio of lead nitrate to potassium iodide and hence the balanced equation. Tell the students that equal volumes of the solutions contain equal numbers of moles of the solutes. The reaction is complete when the
a moles of particles of a substance in a given mass of that substance and vice versa b particles of a substance in a given number of moles of that substance and vice versa c particles of a substance in a given mass of that substance and vice versa identify the type of particles in each substance. 2) Have small, sealed jars containing 1 mole of particles of different substances e.g. 18g of water, 12g of carbon, 32g of sulfur, 56g of iron. Ask the students what they have in common. Explain that taking the relative atomic mass or relative formula mass in grams gives us the mass of 1 mole of that substance and they each contain the same number of particles called the Avogadro constant. Write on the board 602 000 000 000 000 000 000 000, then convert it to standard form: 6.02 x 1023. iron filings (1 g, not rusted), propanone. Students need access to an electronic balance. Optional: access to a warm oven lead nitrate has reacted with all the potassium iodide so there will be no further increase in the amount of precipitate formed. Find the tube where the maximum amount of precipitate first forms. This tube had 4.0 cm3 potassium iodide solution and 2.0 cm3 lead nitrate solution so the number of moles of potassium iodide is twice the number of moles of lead nitrate and the balanced equation is Pb(NO3)2(aq) + 2KI(aq) → PbI2(s) + 2KNO3(aq) Equipment: 2 burettes or graduated pipettes, 8 test tubes in a rack, bungs to fit the test tubes, ruler, lead nitrate solution (25
cm3 0.5 mol dm-3 solution), potassium iodide solution (40 cm3 0.5 mol dm-3 solution) Digital Moles presentation CC9a Acids, alkalis and indicators C3.1 C3.2 C3.3 C3.4 Recall that acids in solution are sources of hydrogen ions and alkalis in solution are sources of hydroxide ions Recall that a neutral solution has a pH of 7 and that acidic solutions have lower pH values and alkaline solutions higher pH values Recall the effect of acids and alkalis on indicators, including litmus, methyl orange and phenolphthalein Recall that the higher the concentration of hydrogen ions in an acidic solution, the lower the pH; and the higher the concentration of hydroxide ions in an alkaline solution, the higher the pH Ask students to write down three or four facts they can remember about about: acids, alkalis and neutral solutions. They then compare their lists in groups. Students test a series of indicators including: litmus, methyl orange and phenolphthalein. by adding an alkali to and acid 1 cm3 at a time while measuring the pH and noting when any colour changes occurs. Students are aware of colour changes for range of indicators and note that the colour change is not always at pH 7 Equipment: TBC Demonstrate the electrolysis of a number of acid solutions: sulfuric acid, nitric acid and hydrochloric acid collect the gas at the negative electrode and test for hydrogen. Link to the idea that acids always contain hydrogen ions Digital TBC
CC9b Looking at acids C3.5 C3.7 C3.8 Recall that as hydrogen ion concentration in a solution increases by a factor of 10, the pH of the solution decreases by 1 Explain the terms dilute and concentrated, with respect to amount of substances in solution Explain the terms weak and strong acids, with respect to the degree of dissociation into ions 1) Demonstrate diluting copper sulfate solution, roughly diluting it by 50% over and over again until the colour cannot seen. Discuss the difference between dilute and concentrated solutions in terms of the amount of solute in a unit volume. Discuss ways of measuring concentrations of solutions eg grams per litre or g dm-3 Equipment: TBC 2) Show students two everyday solutions that contain acids. eg. battery acid and fruit juices. Discuss why you can dink one but not the even though they are about the same concentration? Test the pH of each and Students find out if the pH value is linked to the concentration of the solution. Starting with 0.1 mol dm-3 hydrochloric acid students use accurate measuring apparatus to dilute the solution successively by a factor of 10 The students then use pH meters to measure the pH of the solution (least to highest concentration) This should show the link between pH and concentration. Include questions on concentration and pH. Equipment: TBC Teacher demonstrates the difference in pH between four different solutions of acids with the same concentration eg. hydrochloric acid (pH=1) sulfuric acid (pH=2) , ethanoic acid (pH=4) and carbonic acid (pH=5). Then through class discussion students are introduced to the difference between strong and weak acids and why they will have different pHs. Then show students a fifth solution and measure its pH (should be about 5). Ask students if this is a strong or weak acid? Tell them it is in fact a strong acid, discuss to work out it must be a dilute solution of a strong acid.
initiate class discussion of why these acid solutions might have different PH values and why one might be more acidic than another. Discuss the differences between dilute and concentrated and strong and weak when talking about solutions. Equipment: TBC Digital TBC CC9c Bases and salts C3.9 C3.11 C3.13 C3.15 Recall that a base is any substance that reacts with an acid to form salt and water only Explain the general reactions of aqueous solutions of acids with: a metals b metal oxides c metal hydroxides d metal carbonates to produce salts Describe a neutralisation reaction as a reaction between an acid and a base Explain why, if soluble salts are prepared from an acid and an insoluble reactant: a excess of the reactant is added 1) show what happens to the pH of an acid solution when a range of common neutralisers are added, eg. Toothpaste, indigestion tablets, lime, etc. Students discuss what happens in these reactions and revise the meaning of neutralisation noting what must be happening to the hydrogen ions in the acid 2) Show class some common salt and dissolve it in water. Ask students how they know the salt is still there? Could it have just Students prepare a sample of pure, dry, hydrated copper sulfate crystals. Equipment: TBC Discuss chemical reactions, reactants and products. Show students how to write word and symbol equations, revise formula Digital TBC
25 cm3 volumetric pipette and filler. CC9f Reactions of acids with metals and carbonates C3.11 C3.12 Explain the general reactions of aqueous solutions of acids with (a) metals and (d) metal carbonates to produce salts. Describe the chemical test for (a) hydrogen; (b) carbon dioxide (using limewater) 1) Place a strip of magnesium ribbon in a few cm3 of dilute sulfuric acid in a test tube. Students should observe the effervescence (fizzing). Ask what is in the bubbles. Equipment: eye protection, test tube in a test-tube rack, piece of magnesium ribbon (about 3 cm), dilute sulfuric acid about 5 cm3 of 0.4 mol dm-3) 2) Remind students about ions and ionic bonding. An ion is a charged particle. Cations are formed by the loss of electron(s) and have a positive charge. Anions are formed by the gain of electron(s) and have a negative charge. The ions are held together by electrostatic forces of Students investigate reactions of acids with metals and carbonates to test for carbon and hydrogen. Students will find that magnesium, zinc and iron effervesce with both dilute acids, although iron may not produce enough hydrogen to pop the lighted splint. Copper does not react with dilute acids. All the metal carbonates react with both dilute acids to provide bubbles of a gas that turns limewater turns milky. Equipment: for each group: eye protection, Bunsen burner and heat resistant mat, dropper pipettes, spatula, test tubes, test-tube rack, wooden splints, limewater, small pieces of copper e.g. foil or turnings, magnesium ribbon (1 cm length), granulated zinc (this works better if it is ‘dirty’), copper carbonate (few grams), magnesium carbonate (few grams), dilute hydrochloric acid Summarise the two different methods of preparing soluble salts - from an insoluble reactant and an acid (using metal, base or carbonate) and from a soluble reactant and an acid. Include the general steps in the methods and the general equations. Digital Ionic equations presentation
attraction between the oppositely charged ions. In the solid state, the ions can only vibrate on the spot, but when they dissolve in water, the ions are free to move around. Revise writing ionic formulae from the symbols of common ions, including some with brackets. (few cm3, 1 mol dm-3), dilute sulfuric acid (few cm3, 0.5 mol dm-3), Optional – bung to fit test tube with a delivery tube attached CC9g Solubility C4.19 Recall the general rules which describe the solubility of common types of substances in water: a all common sodium, potassium and ammonium salts are soluble b all nitrates are soluble c common chloride are soluble except for those of silver and lead d common sulfates are soluble except those of lead, barium and calcium e common hydroxides and carbonates are insoluble except those of sodium, potassium and ammonium 1) Pour some potassium chromate(VI) solution into a small glass beaker. Slowly add some silver nitrate solution. Students will see an immediate red precipitate of silver chromate(VI) form. Explain that when two solutions containing soluble salts that react are mixed, the ions swap over, so silver chromate and potassium nitrate are formed. All nitrates are soluble, but silver chromate(VI) is insoluble Students prepare insoluble salts. Students prepare a white precipitate of silver chloride. This precipitate gradually changes colour to purple when left in light, so dry it in a dark place. The copper carbonate is a blue/green precipitate. Equipment: for each group: eye protection, 100 cm3 beaker, 100 cm3 conical flask (or other container to collect filtrate), filter funnel, filter paper, glass rod, 25 cm3 measuring cylinder, dropper pipette, distilled or de-ionised Demonstrate the formation of the same insoluble salt from different solutions e.g. barium sulfate by adding magnesium sulfate, sodium sulfate and copper sulfate solutions to separate portions of barium chloride solution. Explain that it is always the same precipitate that forms as the barium ions are reacting with the sulfate ions. The other ions are spectator ions.
pencil appearing bent when standing in a beaker of water, or a coin in a mug only becoming visible when water is added to the mug. Discuss with the class the basic idea that we see objects because light travels from them to our eyes, and then ask how the pencil could appear bent. Elicit the idea that the light travelling from water to air changes direction. 2) Ask students to work in groups to come up with five key facts about the way light travels and how its direction can be changed. Give them a few minutes, then ask for contributions to a class discussion, recording key points on the board Equipment: glass or plastic blocks of various shapes, including rectangular and triangular; plain paper (A3 if possible); power supply; ray box with single slit (and convex cylindrical lens to make the ray thinner) depth of water. Set up a ripple tank with illumination. Place lamp beneath the ripple tank to project the image onto the ceiling. Make sure the tank is level. The depth of water in part of the ripple tank is reduced by placing a glass block in the tank. The water above the glass should be very shallow and use a low frequency wave. Demonstrate using waves approaching the glass at different angles. Link between changes in wave speed and refraction. Explain that the ripple tank is also acting as model of sound, seismic and light waves refracting. Equipment: Ripple tank and accessories, stopwatches, ruler.