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Edexcel IGCSE Biology: Double Science 復(fù)習(xí)筆記 2.5.10 Humans: Bile

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Edexcel IGCSE Biology: Double Science 復(fù)習(xí)筆記 2.5.10 Humans: Bile

Bile Production

Bile is an?alkaline?substance produced by cells in the?liver
Before being released into the?small intestine?bile is stored in the?gallbladder

Bile-production-and-secretion

Bile production and secretion

Exam Tip

Bile?contains?bile salts,?it is these molecules which emulsify the fats, however you can use both terms interchangeably.

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 fat 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 fat (lipids) 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

Exam Tip

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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