Science at key stage 3    (Year 8)

• Use a true/false quiz to assess and revise pupils' knowledge and understanding of food and diet. Provide a selection of terms used in the quiz and ask pupils to link related terms together. These terms can be used again at the end of the unit when reviewing work to monitor progress in learning. Ask them about work carried out in key stage 2. Review the main reasons why we need food.

• Ask pupils to use the nutritional information panel from cereal packets to identify the main nutrients contained in food, and establish that carbohydrates, proteins, fats, fibre and water form the bulk of food.
• Demonstrate food tests to identify protein, starch, sugars, fats, and water, ensuring that pupils are aware of the health and safety requirements for these tests.
• Provide a range of foods, eg 15 samples, and ask pupils working in groups to use the food tests to identify the presence of nutrients in the foods. Help pupils to share results and produce a Venn diagram showing foods which have different combinations of the nutrients.
• Discuss with pupils the importance of water in the diet, what the sources of water are and whether it should or should not be counted as a nutrient.

• Extend pupils' understanding of a balanced diet by providing software on diet containing information about the nutritional content of a range of foods.
• Depending on the nature of information provided, help pupils to frame appropriate questions to investigate, eg Which foods contain starch and fat?, and to use the spreadsheet to produce and interpret graphs. Ask them to compare the results obtained with the Venn diagram from the previous activity and to suggest reasons for differences.
• Help groups of pupils to use the results of their investigations to produce a summary leaflet about one type of food constituent, including information about foods that are a good source of it and the role of this food constituent in the diet.
• Bring together all the leaflets as a class booklet and establish the main role of each type of food in the diet.

• Introduce the idea that there are many different healthy and balanced diets by inviting pupils from a variety of backgrounds to describe some of the main features of their own or their family's diet. Suggest that pupils ask senior members of their family to describe the type of diet they had when they were children.
• Use food packaging, advertising claims, media reports, or recorded television advertisements as a stimulus to raise questions, eg
• Can too much salt be harmful?
• What is a healthy diet?
• Should children and adults have the same diet?
• Are low-calorie alternatives always preferable?
• How do diets of different cultures differ?
• Raise the issue of what exactly is meant by a 'healthy' balanced diet.

• Ask pupils to use information from a variety of secondary sources to find out more about one question from those already raised by pupils or others, eg
• What foods should you eat to reduce the chance of heart disease?
• What do athletes eat at different stages of training?
• What does a pregnant woman need in her diet?
• What are 'organic' foods and how are they different from other foods?
• Are breakfast cereals really good for you?
• Discuss with pupils what they have found out and the extent to which they have confidence in the information they used.

• Ask pupils to produce a report of their findings and conclusions in an interesting and appropriate format, eg display work, an advisory leaflet for a particular target group, a class debate, a radio interview script.
• Remind pupils about earlier work on food chains and contrast the diet of animals with the range of the human diet.

• Ask pupils to produce a quiz sheet to test knowledge and understanding about food and diet and exchange with other pupils, who can use them to assess their knowledge and understanding.

• Ask pupils for their ideas about what happens to food once it has been eaten. Develop the idea that food enters a tube running through the body, and that this, and associated organs, make up the digestive system. Build up their suggestions into a sequence of events commencing with feeding, followed by absorption and ending with elimination of faeces.
• Explain that what happens to food inside this tube can be explored using a model, eg a model gut made from visking tubing filled with a 'starch meal'; a software simulation. Ask pupils about how they tested for starch earlier and help them to test the contents of the 'gut' and the surrounding water for starch. Ask pupils to explain their observations and to consider the implications of nutrients from food entering the body.
• Ask pupils to interpret their findings in the light of their previous assumptions.

• Check pupils' understanding of the relationship between size of food molecules and ease of absorption, eg by showing them models representing molecules of starch, protein, fat, sugars, vitamins and minerals. Ask pupils which of these make up most of the foods they eat and challenge them to suggest what must happen to the large molecules. Ask them to predict which will be absorbed most easily, with reasons.
• Establish that digestion involves breaking larger molecules into smaller ones. Introduce the idea that digestion involves enzymes which act on large, insoluble molecules to break them down into smaller, soluble molecules. Help pupils to set up a model gut containing saliva and starch, and to test the contents of the water for sugar and the contents of the model gut for starch.

• Through questioning, elicit pupils' ideas about digestive enzymes as a means of breaking down larger molecules. Establish that the water outside the tubing in the model represents the blood system. Ask them to explain the process, eg using animations from CD-ROMs or video, or interlocking bead models of large molecules. Ask pupils to draw a sequence of diagrams and then write an explanation in their own words.

• Remind pupils of the range of food types with large molecules and explain that in addition to enzymes the conditions inside the gut assist the breakdown of large molecules, eg body temperature. Ask the pupils to discuss what other substances are found in the stomach. After the discussion inform the pupils that hydrochloric acid is produced by the lining of the stomach.
• Provide them with an opportunity to investigate the action of a particular enzyme, eg trypsin acting on the gelatine of exposed and developed black-and-white photographic film; protease acting on albumen.
• Ask pupils to suggest what might affect how well the enzyme digests the food, eg pH, temperature, and help them to plan an investigation, identifying what they are going to measure and which variables they will need to control. Ask pupils to produce an account of their investigation, relating what they found out to the conditions in the gut.

• Remind pupils about the way in which the body uses food, eg for energy, for growth, and ask them how the products of digestion reach other parts of the body. Use secondary sources, eg video clips, ICT simulations, to show how simple molecules, eg glucose molecules, are transported to cells, eg in the muscles.
• Ask pupils which of the food types they hadn't considered during the work on the products of digestion. Establish that fibre and undigested food is passed through the gut and egested in faeces.

• Provide pupils with an appropriate selection of terms related to food and digestion and ask them to use these to make a concept map. Discuss pupils' maps with them, asking them to identify areas of difficulty and challenging them to make and explain new connections.