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  • What is the Alimetary Canal?
  • What is the lumen?
  • What is the name of the entry of food into the alimentary canal?
  • What is the definition of digestion ?
  • What is mechanical digestion?
  • What is chemical digestion?
  • What is absorption?
  • What is egestion ?
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Glossary answers

  • The alimentary canal is the tube running from the mouth to the anus
  • The middle of the alimentary canal is a lumen, which is technically still outside the body
  • Ingestion
  • Digestion is the breakdown of polymers into monomers small enough to enter cells 
  • Primates chew their food and mammalian stomach churns it increasing the surface area (MECHANICAL)
  • Large surface area allows better access for enzymes which catalyse the hydrolysis of polymers into their monomer subunits (CHEMICAL)
  • Absorption is the movement of small molecules (water, inorganic ions, vitamins) + products of digestion from the lumen into cells in the wall of the canal, then into the bloodstream.
  • Food which cannot be digested or absorbed. It passes through the canal and leaves from the anus as faeces by egestion.
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How are proteins digested ?

1.Endopeptidases - break down bonds between amino acids in the interior of the molecule which produces smaller polypeptides e.g. pepsin and trypsin

2.Exopeptidases - break down smaller polypeptides. These break off the end of amino acids. There are two types:

  • aminopeptidases - break down free amino acid group end
  • carboxypeptidases - break down free carboxyl group end
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Absorption in the small intestine.

Absorption occurs accross epithelial cells by facilitated diffusion and active transport, relying largely on Na+ cotransport. 

Describe how the small intestine is adapted for the absorption of soluble food.

  • Large surface area provided by villi/microvilli
  • folds increase surface area
  • Long; increasing time for absorption
  • Thin epithelium gives a short diffusion pathway
  • Capillary network absorbs amino acids/sugars; into blood
  • Lacteal for absorption of digested fats
  • Abundant mitochondria in epithelial cells supply energy for active transport
  • Epithelial cells have carrier proteins for facilitated diffusion/active transport.
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