Bile (Edexcel IGCSE Biology)

Revision Note

Lára Marie McIvor

Last updated

Bile Production & Storage

  • 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

Bile production and secretion

Examiner Tips and Tricks

Bile contains bile salts. It is these molecules which emulsify the lipids, however you can use both terms interchangeably.

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The Role of Bile

  • 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

    2. 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 and emulsification

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

Examiner Tips and Tricks

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.

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Lára Marie McIvor

Author: Lára Marie McIvor

Expertise: Biology Lead

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.