The digestive system of a human being. Image credit MediaWiki

ZIMSEC O Level Combined Science Notes: The digestion process

  • Food is broken down in the alimentary system from large pieces/molecules into smaller molecules.
  • The food most mammals ingest is in large pieces e.g. leaves, grass, cake, meat etc.
  • All mammals have teeth to bite off the food and chew it.
  • Food is broken down into smaller molecules by the chewing acting of teeth.
  • Mechanical┬ádigestion this is when food is broken down by the chewing action of teeth.
  • This is physical change.
  • The strong muscular walls of the oesophagus and the stomach also help in breaking down food into smaller pieces.
  • Juices from the salivary glands and the stomach are also mixed with the food.
  • Insert peristalsis diagram here.
  • Peristalsis- the action by which muscles push the food down along the alimentary canal.
  • The muscular walls around the food contract to squeeze the food along the tube.
  • The muscles in front of the food relax.
  • As food passes along the tube the small pieces of food are also chemically changed.7
  • Large molecules are converted into smaller ones.
  • This process is carried out by enzymes.
  • Enzyme-is a special molecule that speeds up a chemical reaction.
  • They are biological catalysts.
  • Enzymes are found in all living cells and in digestive juices such as saliva.
  • The enzyme molecules become attached to the food molecules and split them into smaller ones.
  • Enzymes can act on food more easily if it is in smaller pieces.
  • This results in a larger surface area for them to act on.
  • This is achieved by chewing which results in food pieces becoming smaller and presenting a larger surface area.

To access more topics go to the Combined Science Notes page.

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