Science at key stage 3    (Year 8)

• Ask pupils for their ideas about why the body needs food, reminding them of work done in unit 8A 'Food and digestion'. Explain that this unit will concentrate on how cells release energy for growth, synthesis of new materials and body heat.

• Ask pupils about 'high energy' drinks, who uses them and what they contain, and provide pupils with secondary sources of information. Establish that glucose is a major constituent of such drinks/foods and ask pupils to relate this to what they learnt about digestion of carbohydrates (starches) in unit 8A 'Food and digestion'. Use secondary sources, eg video clips, software simulations, to show how small molecules, eg glucose, are transported in the blood to other parts of the body, eg muscles, brain.

• Remind pupils of work they did in earlier units on fuels and, by questioning, establish that when fuels burn they react with oxygen and release energy. Demonstrate this using 2.5cm of icing sugar in a tin-can 'bomb', igniting the fine powder with the flame of a candle and showing that this type of dust explosion can blow off the can lid. Emphasise that the chemical reaction in cells is much more controlled than the dramatic demonstration. Explain that, although burning does not occur, a similar reaction takes place between glucose and oxygen in the cells of the body and that this is aerobic respiration.

• Present pupils with a range of observation activities, eg
• observing a temperature difference between germinating peas and boiled peas
• yeast generating bubbles of carbon dioxide which are passed into lime water
• germinating peas and maggots in separate gauze cages over hydrogencarbonate indicator
• water weed shielded by black paper in hydrogencarbonate solution producing carbon dioxide
• measuring their own temperature
• Discuss their observations to establish that the hydrogencarbonate indicators show that the living material was producing carbon dioxide and the increased temperature measured by the thermometers shows that the living material was also releasing energy. Provide pupils with opportunities to discuss, in groups, what they observe and provide an explanation to the whole class.
• Explain that energy is released in cells by respiration, which is a process that uses nutrients from food and oxygen, and releases carbon dioxide, water and energy. Summarise the process of aerobic respiration in a word equation.

• Ask pupils what they know about the heart and circulation of blood in humans. Provide pupils with a simple diagram of blood circulation or a card sort/sequence and labels activity. Ask pupils to describe the route glucose takes from the stomach to reach a leg muscle cell. Establish that oxygen enters the body through the lungs and ask pupils to describe the route oxygen takes from the lungs to a leg muscle cell.

• Remind pupils of the heart's structure and function using, eg illustrations, video clips, models, mammalian hearts, CD-ROMs. Discuss the heart's pumping action as a double pump, one side supplying the lungs, the other side supplying the other body organs. Provide opportunities for pupils to discuss in groups and then annotate diagrams of the heart using arrows to show the direction of blood flow. Ask pupils to think about and predict the consequences of the heart not working efficiently in terms of blood supply to the tissues and lungs.
• Provide pupils with secondary sources so that they can find out about the development of ideas about the heart and circulation and scientific methods using, eg Galen, Vesalius, Harvey, Withering, Ibn-al-Nafis. Help them to draw out the ideas about experimenting and making inferences. Emphasise that scientific theories were based on persuasive argument and that there were long periods of time before ideas, even though not supported by evidence, changed.

• Remind pupils of earlier work and review their understanding of the reaction in the cells between oxygen and glucose. Ask them to think about what happens if the blood cannot supply enough oxygen for the cell's needs, eg during intense physical activity.
• Ask them about their own experiences and illustrate, eg with video clips of athletics. Ask pupils about the meaning of the word 'aerobic' and why aerobics in relation to exercise is so called.
• Extend to other situations where there may be a reduced oxygen supply, eg through illness, mountaineering. Reinforce the idea that carbon dioxide and water, as well as energy, are released from aerobic respiration and that carbon dioxide is removed from the cells in the bloodstream.

• Provide pupils with a series of true/false statements or flashcards about respiration and the transport role of blood. Ask them to work in groups to classify the statements and to provide reasons for their choices. They should be shown how to discuss and respond to initial ideas and information, carry out the task, and then review and refine ideas. Use the work to form the basis of a summary of key points.

• Review, using quick questions, pupils' understanding of the composition of air breathed into the lungs and the importance of oxygen for aerobic respiration. Ask pupils to suggest what happens to air when it enters the lungs. Establish, eg using simulation software, that oxygen enters the blood and is transported elsewhere, and that carbon dioxide produced in the cells passes out of the blood.
• Show illustrations, models or animated pictures of the fine structure of the lungs and ask pupils to suggest why the alveoli have so many blood vessels around them. Provide information about carbon dioxide and oxygen concentrations in the blood. Ask pupils to predict what happens in the alveolus. Help pupils to annotate diagrams with arrows to show the direction of movement of oxygen and carbon dioxide and describe gas exchange in terms of a supply of oxygen to the blood and removal of carbon dioxide from the blood.
• Show illustrations of damaged lungs from, eg emphysema, dust damage. Ask the pupils to describe the differences and predict what effects this damage may have on gas exchange.

• Ask pupils to use what they know about respiration to predict the differences between inhaled and exhaled air.
• Show pupils how to demonstrate changes in oxygen concentration, eg length of time a candle burns in exhaled air compared to normal air, volume changes when oxygen is absorbed by alkaline pyrogallate. Ask pupils to investigate other changes in the air as they breathe in and out, eg presence of more carbon dioxide in expired air, pupils breathe onto cold mirrors or glass and test the moisture with cobalt chloride paper. Discuss the results with the pupils. Ask pupils to use reference sources to present their findings, including a table of changes in composition of air when it is breathed. Relate this to knowledge of respiration, deciding whether their predictions were correct.
• While the pupils are waiting for results, ask them to use reference sources to find out how aquatic animals and plants obtain oxygen from water.

• Ask pupils about the organisms they used earlier in the unit and ask them how they could find out if other living things also produce carbon dioxide during respiration. Provide suitable apparatus for holding living material, eg gauze platform in a boiling tube above a hydrogencarbonate indicator solution.
• Discuss the selection of living organisms, eg yeast, germinating lentils, small fruit woodlice, maggots, the use of a control apparatus without living material and relevant factors, eg mass of living material, temperature, activity, sensitivity of the indicator, length of time to leave it. Ask the pupils to write a plan for their investigation.

• Help pupils to carry out the investigation they planned. Compare results from different investigations and ask the pupils to identify any trends, eg plant material produced less carbon dioxide than animal material, the more active animals produced more carbon dioxide.
• Draw together the results of the investigations and establish respiration as a process that takes place in the cells of plants and animals.

• Provide pupils with a diagram showing the gut, lungs, blood supply, heart and cells, and help them to produce a flow chart showing how expired carbon dioxide is derived from glucose, made available by digestion, and its reaction with inhaled oxygen.
• As appropriate, supply pupils with prepared phrases with which to label the flow chart and/or structured questions.