Cambridge O Level Biology · Syllabus 5090 · Excretion
Egestion
What is Egestion?
The removal through the anus of undigested and unabsorbed food that has passed along the alimentary canal. The material removed by egestion was never inside a body cell and was never produced by a chemical reaction of the body, so faeces is not a waste product of metabolism and egestion is not a form of excretion. The contrast with excretion, which removes substances that cells made or that the body has in excess, is a frequently examined distinction in Cambridge O Level Biology.
This definition is part of the Excretion chapter in Cambridge O Level Biology.
Common mistakes with Egestion
- “Excretion means removing faeces from the body.” Why wrong Faeces is undigested and unabsorbed food. It was never inside a cell and no reaction of the body produced it, so it is not a waste product of metabolism. Say instead Excretion is the removal of toxic materials, the waste products of metabolism and substances in excess of requirements. Removing faeces is egestion.
- “Egestion removes metabolic waste.” Why wrong This is the previous error running the other way. Egestion removes material that stayed in the alimentary canal from beginning to end. Say instead Egestion removes undigested and unabsorbed food through the anus.
Questions students ask about Egestion
What is the difference between excretion and egestion?
Excretion removes substances the body's own cells produced, or substances present in excess. Egestion removes undigested and unabsorbed food through the anus. The material removed by egestion never entered a cell and was never produced by a chemical reaction of the body, which is why faeces is not a waste product of metabolism.