Excretion in Humans (Cambridge International IGCSE Biology)
Excretion of carbon dioxide & urea
Spec point —
13.1.1· State that carbon dioxide is excreted through the lungs State that the kidneys excrete urea and excess water and ions Identify in diagrams and images the kidneys,ureters, bladder and urethra
Excretion of carbon dioxide & urea
What is the excretory system?
- The human excretory system is a group of organs which are specialised for the removal of certain excretory products
- Two important organs in the human excretory system are the lungs and kidneys
| 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?
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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
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Carbon dioxide must be excreted as it dissolves in water easily to form an acidic solution, lowering 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
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Urea is also toxic to the body in higher concentrations and so must be excreted
The excretory system in humans
The main components of the excretory system
| Structure | Role |
|---|---|
| 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 |
Exam Hint Note the difference between the ‘ureter’ and the ‘urethra’. These two names are commonly confused so take care to learn them and know which tube is which – they are not interchangeable!
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