Bile (Edexcel IGCSE Science)

Bile Production & Storage

Spec point — 2.30 · understand that bile is produced by the liver and stored in the gall bladder

• Bile is an alkaline substance produced by cells in the liver
• Before being released into the small intestine, bile is stored in the gall bladder

Bile production and secretion

Exam Hint Bile contains bile salts, which emulsify lipids. In exam answers, it is usually acceptable to say that “bile emulsifies lipids,” but the molecule responsible is actually the bile salts.

The Role of Bile

Spec point — 2.31 · understand the role of bile in neutralising stomach acid and emulsifying lipids

• Bile has two main roles:

  1. Neutralising the hydrochloric acid from the stomach
  • The alkaline properties of bile allow for this to occur
  • This neutralisation is essential as enzymes in the small intestine have a higher (more alkaline) optimum pH than those in the stomach
  1. Breaking apart large drops of lipids (fats) into smaller ones(and so increasing their surface area)
  • This is known as emulsification

• The more alkaline conditions and larger surface area allows lipase to chemically break down the lipid molecules into glycerol and fatty acids at a faster rate

Bile salts break large lipid droplets into smaller ones with a larger surface area

Exam Hint Emulsification is the equivalent of tearing a large piece of paper into smaller pieces of paper. This is an example of mechanical digestion, not chemical digestion – breaking something into smaller pieces does not break bonds or change the chemical structure of the molecules which make it up, which is the definition of chemical digestion.