Excretion is the removal of the following substances:

  • toxic materials
  • waste products of metabolism
  • excess substances from organisms

Excretion is not the same as egestion - which is the passing out of undigested food through the anus as faeces.


Plants need to excrete excess carbon dioxide and oxygen. Carbon dioxide is a waste product of aerobic respiration in plant cells. Oxygen is a waste product of photosynthesis.

The leaf

Unlike animals, plants do not have specialised excretory organs. Excess carbon dioxide and oxygen are excreted from the plant through the stomata in the leaves.

Leaf structure. Four layers. Top is upper layer, then palisade layer, spongy layer and lower layer. Sunlight hits upper layer. Exchange of gases to and from spongy and lower layer.Gas exchange through the stomata