Chemical digestion
Chemical digestion
- Chemical digestion breaks large insoluble molecules into small soluble ones.
- Only small soluble molecules can be absorbed into the blood.
- Enzymes do this work.
The digestive enzymes
| Enzyme | Breaks down | Into |
|---|---|---|
| amylase | starch | reducing sugars |
| protease | protein | amino acids |
| lipase | fats | fatty acids + glycerol |
Practice
Amylase breaks down:
Amylase digests starch to sugars; protease → amino acids; lipase → fatty acids + glycerol.
Practice
Protease breaks down protein into:
Protease digests protein into amino acids.
Practice
Lipase breaks down fats into:
Lipase digests fats and oils into fatty acids and glycerol.
Stomach acid
- The stomach makes hydrochloric acid, which:
- kills microorganisms in the food, and
- gives the acidic pH that the stomach's protease works best at.
- (Supplement) pepsin works in the acidic stomach; trypsin in the alkaline small intestine; bile neutralises the acid entering the duodenum.
Practice
Hydrochloric acid in the stomach:
Stomach acid kills microbes and provides the acidic pH for the stomach's protease.
You've got it
Key idea
- chemical digestion = large insoluble → small soluble molecules, done by enzymes
- amylase → sugars; protease → amino acids; lipase → fatty acids + glycerol
- stomach acid kills microbes and gives the low pH for its protease