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Science at key stage 3 (Year 8)
Unit 8A: Food and digestion
Section 9: b. What happens to food inside the digestive system?
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Objectives |
| Children should learn: |
- that foods contain starch, protein and fat, which have molecules that are too large to be absorbed by the body
- that sugars, vitamins and minerals are generally smaller and can be absorbed by the body
- that large molecules are broken down by enzymes in the gut to form smaller molecules, which pass through the wall of the small intestine
- how models can be used to represent and explain complex processes
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Activities |
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Outcomes |
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Children: |
- 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.
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- state that small molecules can pass through the wall of the small intestine
- explain that starch, protein and fat molecules are too large to be absorbed
- explain that specific vitamins and minerals are generally smaller and can be absorbed by the body
- produce a sequence of diagrams to illustrate that larger molecules are broken down to form smaller molecules in the gut
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Points to note |
- Plants' production of starch from glucose for storage is introduced in unit 9A 'Inheritance and selection'. Minerals,
eg calcium, and vitamins,
eg vitamin C, are considered in more detail in unit 9B 'Fit and healthy'.
- Interlocking bead models can be used to represent large and small molecules and to model the process of breakdown of molecules, such as starch into sugar molecules. Although such models do not accurately represent the structure of fats, they do help to get across the idea of complexity.
Safety
- ensure pupils use their own saliva and that used test tubes are placed in disinfectant. Staff who clean apparatus should use gloves
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This unit is divided into sections. Each section contains a sequence of
activities with related objectives and outcomes. You can view this unit by
moving through the sections or print/download the whole unit.
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