Biology (Separate Science) · GCSE · AQA · AQA GCSE Biology - Foundation (8461) · Specification point · 4.2.2.1 · Organisation · Animal tissues, organs and organ systems
4.2.2.1 The human digestive system
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This section assumes knowledge of the digestive system studied in Key Stage 3 science. The digestive system is an example of an organ system in which several organs work together to digest and absorb food. Students should be able to relate knowledge of enzymes to Metabolism. Students should be able to describe the nature of enzyme molecules and relate their activity to temperature and pH changes. | |
Students should be able to carry out rate calculations for chemical reactions. Enzymes catalyse specific reactions in living organisms due to the shape of their active site. | MS 1a, 1c |
Students should be able to use the ‘lock and key theory’ as a simplified model to explain enzyme action. Students should be able to recall the sites of production and the action of amylase, proteases and lipases. Students should be able to understand simple word equations but no chemical symbol equations are required. |
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Digestive enzymes convert food into small soluble molecules that can be absorbed into the bloodstream.
Carbohydrases break down carbohydrates to simple sugars. Amylase is a carbohydrase which breaks down starch.
Proteases break down proteins to amino acids.
Lipases break down lipids (fats) to glycerol and fatty acids.
The products of digestion are used to build new carbohydrates, lipids and proteins. Some glucose is used in respiration.
Bile is made in the liver and stored in the gall bladder. It is alkaline to neutralise hydrochloric acid from the stomach. It also emulsifies fat to form small droplets which increases the surface area. The alkaline conditions and large surface area increase the rate of fat breakdown by lipase.
WS 1.2 Students should be able to use other models to explain enzyme action. |
Required practical activity 4: use qualitative reagents to test for a range of carbohydrates, lipids and proteins.
To include: Benedict’s test for sugars; iodine test for starch; and Biuret reagent for protein.
AT skills covered by this practical activity: AT 2 and 8.
This practical activity also provides opportunities to develop WS and MS. Details of all skills are given in Key opportunities for skills development.
Required practical activity 5: investigate the effect of pH on the rate of reaction of amylase enzyme.
Students should use a continuous sampling technique to determine the time taken to completely digest a starch solution at a range of pH values. Iodine reagent is to be used to test for starch every 30 seconds. Temperature must be controlled by use of a water bath or electric heater.
AT skills covered by this practical activity: AT 1, 2, 5 and 8.
This practical activity also provides opportunities to develop WS and MS. Details of all skills are given in Key opportunities for skills development.