Bile

Structure and functions in living organisms · Human nutrition · note 5 of 6

Spec 2.30, 2.31Download all Human nutrition notes (PDF)Download all notes (PDF)8 pages

BileSpec 2.30, 2.31

In short

Bile is an alkaline liquid produced by the liver, stored in the gall bladder and released into the duodenum. It neutralises the acid from the stomach, giving the enzymes in the small intestine the alkaline conditions they work best in. It also emulsifies lipids into tiny droplets, increasing their surface area so lipase digests them faster.

Bile is produced by the liver and stored in the gall bladder. It is released into the small intestine (the duodenum).

Bile has two roles in digestion:

It is alkaline, so it neutralises the acid that comes from the stomach. This gives the enzymes in the small intestine the alkaline conditions they work best in.
It emulsifies lipids: it breaks large drops of fat into many tiny droplets. This increases the surface area of the lipid.

The larger surface area lets lipase work faster, so the lipid is digested more quickly.

Common mistake:

Bile is not an enzyme and it does not chemically digest lipids. It only emulsifies them (physical breaking up) so that lipase can work faster. Emulsify is not the same as digest.

Written and checked against the Edexcel IGCSE Science Double Award (4SD0) specification · Updated October 2026

Frequently asked questions

What enzymes digest carbohydrates?

Amylase and maltase digest carbohydrates. Amylase, made in the salivary glands and the pancreas, breaks starch down into the sugar maltose. Maltase, made in the small intestine, then breaks maltose down into glucose. Glucose is small and soluble, so it can be absorbed into the blood in the small intestine and used in respiration.

What enzymes break down proteins?

Proteases break down proteins into amino acids. Proteases are made in the stomach, the pancreas and the small intestine. Pepsin is a protease in the acidic stomach and works best at about pH 2. The amino acids are absorbed into the blood and used to make new proteins for growth and repair.

What enzymes does the pancreas produce?

The pancreas produces amylase, protease and lipase and releases them into the duodenum. Amylase breaks starch into maltose, protease breaks proteins into amino acids, and lipase breaks lipids into fatty acids and glycerol. The pancreas is not part of the alimentary canal itself, but it helps with digestion.

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