Chemical digestion
Introduced| English | Meaning |
|---|---|
| chemical digestion/ˈkemɪkl daɪˈdʒestʃn/ | chemical digestion |
| carbohydrases/ˌkɑːbəʊˈhaɪdreɪzɪz/ | carbohydrases |
| amylase/ˈæmɪleɪz/ | An enzyme that breaks starch into smaller sugars. |
| proteases/ˈprəʊteɪsɪz/ | proteases |
| lipases/ˈlɪpeɪsɪz/ | lipases |
| neutralises/ˈnjuːtrəlaɪzɪz/ | Cancels acidity or alkalinity to bring the pH towards neutral. |
Breaking food apart — chemically
- Physical digestion makes food smaller; chemical digestion 化学消化 breaks the big molecules into small, soluble ones the body can absorb.
- This is done by digestive enzymes.
Amylase digests:
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Amylase is a carbohydrase acting on starch.
Match each enzyme to what it digests.
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Each enzyme acts on one type of food molecule.
Lipase breaks fats down into:
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Lipase produces fatty acids and glycerol.
Proteins are digested into ______ acids.
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Protease breaks protein into amino acids.
The three enzyme groups
- Carbohydrases 碳水化合物酶 (e.g. amylase 淀粉酶): break carbohydrates → simple sugars.
- Proteases 蛋白酶: break proteins → amino acids.
- Lipases 脂肪酶: break fats → fatty acids and glycerol.
A tooth in section: enamel over dentine, a soft pulp, and a root held by cement
How fast a digestive enzyme works
Add more substrate and the reaction rate climbs, then levels off as every enzyme is busy — the same way amylase, protease and lipase break down food.
Bile neutralises stomach acid so enzymes in the small intestine work at their optimum pH.
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The small intestine is alkaline; bile raises the pH.
Where they work
- Amylase (mouth and pancreas) digests starch.
- Protease (stomach, pancreas) digests protein.
- Lipase (pancreas) digests fat.
Conditions matter
- The stomach is acidic (good for its protease); the small intestine is alkaline.
- Bile neutralises 中和 stomach acid so intestinal enzymes work at their optimum pH.
Worked example. Starch is digested by amylase into maltose, then into glucose — small enough to be absorbed into the blood. Big molecule in, small soluble molecule out.
You've got it
- carbohydrases → sugars; proteases → amino acids; lipases → fatty acids + glycerol
- amylase digests starch, protease digests protein, lipase digests fat
- enzymes need the right pH; bile neutralises stomach acid for the small intestine