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Study Guide : Diet – Continued



There are different types of enzymes, which break down different molecules.

  • Amylase breaks down carbohydrates into simple sugars
  • Protease enzymes helps to form amino acids from proteins
  • Lipase enzymes break down lipids into glycerol and fatty acids




Different molecules are absorbed and digested in different



Carbohydrates are initially digested in the mouth as salivary

glands release enzymes; it is continued in the stomach and

the small intestine and finally absorbed in the small intestine.


Proteins are digested in the stomach by the stomach acid and

are absorbed in the small intestine.


The stomach initially digests lipids, and then bile is released

into the small intestine, which helps to digest the lipids even

further. The fatty acids and glycerol are then absorbed in the

small intestine.


Humans do not possess the enzymes to break down dietary

fibre so therefore it cannot be absorbed.


The small intestine

The small intestines have many adaptations to ensure that

absorption occurs as efficiently as possible.

The main adaptations are:

  • Large surface area achieved by the small finger like projections called villi
  • Short diffusion distance achieved by having the barrier only one cell thick
  • Large blood supply ensuring the absorbed nutrients can be carried to the rest of the body

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