Chemical Digestion (Cambridge (CIE) IGCSE Biology)

Chemical Digestion

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

•  The role of chemical digestion is to produce small soluble molecules that can be absorbed