Digestive System (CIE IGCSE Biology: Co-ordinated Sciences (Double Award))

The human digestive system

Stages of food breakdown

• Food taken into the body goes through 5 different stages during its passage through the alimentary canal (the gut):
  • Ingestion - the taking of substances, e.g. food and drink, into the body through the mouth
  • Mechanical digestion - the breakdown of food into smaller pieces without chemical change to the food molecules
  • Chemical digestion - the breakdown of large, insoluble molecules into small, soluble molecules
  • Absorption - the movement of small food molecules and ions through the wall of the intestine into the blood
  • Assimilation - the movement of digested food molecules into the cells of the body where they are used, becoming part of the cells
  • Egestion - the passing out of food that has not been digested or absorbed, as faeces, through the anus

Functions of the Digestive Organs Table