The digestive systemSpec 4.2.2.1
In short
The digestive system is an organ system in which several organs work together to digest and absorb food. Large molecules of carbohydrate, protein and lipid are too big to pass into the blood, so digestive enzymes convert them into small soluble molecules. Digestion is finished in the small intestine, where these molecules are absorbed into the bloodstream.
The digestive system is an example of an organ system in which several organs work together to digest and absorb food.
Food contains large molecules of carbohydrate, protein and lipid. These are too big to pass into the blood. Digestive enzymes convert food into small soluble molecules that can be absorbed into the bloodstream.
| Organ | Role |
|---|---|
| Salivary glands | Make amylase, which mixes with food in the mouth |
| Stomach | Churns food. Makes protease and hydrochloric acid |
| Liver | Makes bile |
| Gall bladder | Stores bile |
| Pancreas | Makes amylase, protease and lipase, and releases them into the small intestine |
| Small intestine | Makes amylase, protease and lipase. Digestion is finished here and the small soluble molecules are absorbed into the blood |
(opens full size in a new tab)Digestion breaks big molecules into small ones. Absorption is the movement of the small molecules into the blood. Do not mix up the two words.
Written and checked against the AQA GCSE Combined Science (8464) specification · Updated October 2026