Pre Knowledge 1

The importance of excretion in humans and other animals

Homeostasis, the maintenance of a steady internal state, is essential for cell functioning. Cell metabolism is controlled by enzymes which catalyse each chemical reaction in living organisms. Enzymes are extremely sensitive to temperature and pH and they are substrate specific and they do not function effectively when there is an accumulation of waste products or the optimal concentrations of water and dissolved substances are not maintained. The excretory system regulates the concentrations of essential substances and wastes in the internal environment by : removing wastes, maintaining optimal water and salt levels (osmoregulation), maintaining blood pH and blood volume.