A-LEVEL BIOLOGY AQA NOTES 
digestion and absorption

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Digestion
  • During digestion, large biological molecules are hydrolysed to smaller molecules that can be absorbed across cell membranes
  • Digestion enzymes in mammals includes:
  • The ileum is the final section of the small intestine where both hydrolysis and absorption occurs.
  • Bile salts made by the liver, emulsify lipids in order to increase the surface area of the lipids, for greater access to lipases.
  • Micelles are the products of lipase digestion that remain in association with the bile salts to form structures. The micelles travel to the ileum where, upon contact with the surface of ileum epithelium cells, they are broken down. This releases the non-polar monoglyceride and fatty acids, which diffuse straight into the epithelial cell.
  • Amino acids and carbohydrates are absorbed via co-transportation with sodium.