Amylase, proteases and lipasesSpec 4.2.2.1
In short
Amylase, a carbohydrase, breaks down starch into simple sugars. Protease breaks down proteins into amino acids, and lipase breaks down lipids into glycerol and fatty acids. Amylase is made in the salivary glands, pancreas and small intestine; protease in the stomach, pancreas and small intestine; and lipase in the pancreas and small intestine.
Three types of digestive enzyme break the three main food molecules into small, soluble molecules. You need to recall where each is made and what it does.
Digestive enzymes| Enzyme | Breaks down | Into | Made in |
|---|
| Amylase (a carbohydrase) | Starch | Simple sugars | Salivary glands, pancreas, small intestine |
|---|
| Protease | Proteins | Amino acids | Stomach, pancreas, small intestine |
|---|
| Lipase | Lipids (fats) | Glycerol and fatty acids | Pancreas, small intestine |
|---|
Carbohydrases break down carbohydrates to simple sugars. Amylase is a carbohydrase which breaks down starch.
You only need simple word equations, not chemical symbol equations.
starch → simple sugars (catalysed by amylase)
protein → amino acids (catalysed by protease)
lipid (fat) → glycerol + fatty acids (catalysed by lipase)
The products of digestion are used to build new carbohydrates, lipids and proteins. Some glucose is used in respiration.
Exam tip:Learn the pairs: amylase with starch, protease with protein, lipase with lipid. The names of the products are what mark schemes ask for.
Written and checked against the AQA GCSE Biology (8461) specification · Updated October 2026
Frequently asked questions
Why do enzymes denature at high temperatures?
At high temperatures the shape of the enzyme's active site changes, so the substrate no longer fits and the reaction cannot be catalysed. The enzyme is denatured, and this cannot be changed back. Below the optimum, the rate rises with temperature because particles move faster and collide more often. Enzymes are not killed, because they are not alive.
How are alveoli adapted for gas exchange?
Millions of alveoli give a very large surface area for diffusion. Their walls are one cell thick, so the diffusion distance is short. A network of capillaries carries oxygen away and brings carbon dioxide, and constant ventilation brings fresh air. Both keep a steep concentration gradient, so oxygen diffuses into the blood and carbon dioxide diffuses out quickly.
Why is the left ventricle thicker than the right?
The left ventricle has a thicker muscular wall than the right because it pumps blood all the way around the body at a higher pressure. The right ventricle only pumps blood to the lungs. Both are part of the double circulatory system, in which blood passes through the heart twice on each complete circuit.
All 5 questions on Animal tissues, organs and organ systems
