- Unlike plants, humans have organs which are specialised for the removal of certain excretory products
- They include the lungs and kidneys
- The liver also has a vital role in excretion
Organs involved in excretion
- Excretion is the removal of the waste substances of metabolic reactions (the chemical reactions that take place inside cells), toxic materials and substances in excess of requirements
- Carbon dioxide must be excreted as it dissolves in water easily to form an acidic solution which can lower the pH of cells
- This can reduce the activity of enzymes in the body which are essential for controlling the rate of metabolic reactions
- For this reason, too much carbon dioxide in the body is toxic
- Urea is also toxic to the body in higher concentrations and so must be excreted
The urinary system in humans
Main structures involved:
