Excretion
- ICSE Class 10, Unit 3 Human Anatomy and Physiology
Excretion is the removal from the body of wastes made by its own cells, chiefly nitrogen wastes such as urea.
Your cells use food and make waste as they work. When the body breaks down extra protein, the liver turns the nitrogen part into urea. Urea is harmful if it builds up, so it must go. Several organs share the work:
- Kidneys: urea, salts and extra water, as urine.
- Skin: water, salts and a little urea, as sweat.
- Lungs: carbon dioxide and water vapour.
Excretion is not the same as egestion. Egestion is getting rid of undigested food as faeces. That food was never part of the body's cells, so it is not excretion.
A small example
After a meal of dal, the protein is digested and used. The part your body cannot store is broken down, and urea forms. Your kidneys filter it out, and it leaves in urine. Urine is the liquid; urea is the waste inside it.
Where marks go
The 2025 ICSE Biology paper asked candidates to explain excretion, for 1 mark. The marking scheme wants the removal of nitrogenous wastes, or urea. CISCE's report on the 2025 Biology paper names confusion with egestion and defecation, and answers that did not say the waste is nitrogenous.
In 2024, the paper asked for the main nitrogenous waste. CISCE's 2024 report records "urine" written instead of "urea". One word decides the mark, so learn definitions with their key words.
Sources
Facts last checked against these sources on 30 September 2026.
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