Excretion in Humans (Cambridge (CIE) IGCSE Biology)
Revision Note
Written by: Lára Marie McIvor
Reviewed by: Lucy Kirkham
The excretory system
What is the excretory system?
The human excretory system is a group of 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
Organ | Mainly Excretes | Explanation |
|---|---|---|
Lungs | Carbon dioxide | The lungs excrete carbon dioxide (the waste product of aerobic respiration) during exhalation |
Kidneys | Excess water, salts and urea | The kidneys excrete excess water, salts and urea (produced in the liver from excess amino acids) through the formation of urine |
What is 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 excretory system diagram
The excretory system in humans
The main components of the excretory system:
Structure | Explanation |
|---|---|
Kidney | Two bean-shaped organs that filter the blood |
Ureter | Tube connecting the kidney to the bladder |
Bladder | Organ that stores urine (excess water, salts and urea) as it is produced by the kidney |
Urethra | Tube that connects the bladder to the exterior; where urine is released |
Examiner Tips and Tricks
Note the difference between the ‘ureter’ and the ‘urethra’. These two names are commonly confused by students so take care to learn them and know which tube is which – they are NOT interchangeable!
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