AQA · Biology · 8461
GCSE Biology: The human digestive system
Organisation · AQA GCSE Biology (8461), specification point 4.2.2.1. Cards are generated from the exam board's own specification for "The human digestive system", and every card links back to the page it came from. Specification © AQA — used with attribution.
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Why do enzymes catalyse only specific reactions?
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Because of the shape of their active site — only a substrate that fits the active site can react.
What is the 'lock and key theory' of enzyme action?
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A simplified model in which the substrate (key) fits exactly into the enzyme's active site (lock).
What is the function of digestive enzymes?
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They convert food into small soluble molecules that can be absorbed into the bloodstream.
Amylase is a carbohydrase that breaks down ?.
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starch
What do proteases break proteins down into?
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Amino acids.
What are the products of lipid digestion by lipase?
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Glycerol and fatty acids.
Where is bile made?
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In the liver (it is then stored in the gall bladder).
Bile is stored in the ?.
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gall bladder
Why is bile alkaline?
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To neutralise hydrochloric acid from the stomach, giving the alkaline conditions lipase needs to work.
How does bile emulsifying fat speed up its digestion?
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It breaks fat into small droplets, increasing the surface area for lipase to act on.
Which reagent is used to test for starch?
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Iodine solution.
Which reagent is used to test for protein?
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Biuret reagent.
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