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GCSE Biology · key term
The removal from an organism of waste products made by its metabolism, such as urea.
Used by AQA, Edexcel and OCR
Specification 4.5.3.3, 4.7.4.3 · Paper 2
The removal from an organism of waste products produced by metabolism, including urea and carbon dioxide.
Revise: Excretion and the Formation of UreaExcretion is the removal of metabolic waste from the body. Metabolic wastes are made by chemical reactions in cells. Urea is one such waste, so removing it in urine is excretion.
Specification 8.1 · Paper 2
Removal from an organism of waste products of metabolism and substances present in excess.
Specification B4.1i · Paper 2 (Foundation), Paper 4 (Higher)
The removal of waste substances made by metabolic processes, such as urea or carbon dioxide.
Revise: Pyramids of biomassAnimals also remove waste made by processes inside their cells. This is excretion. For example, a rabbit excretes urea in urine rather than adding that material to its body.
Paper 1 (Foundation), Paper 2 (Foundation), Paper 3 (Higher), Paper 4 (Higher)
The removal of waste products made by metabolism, such as carbon dioxide or urea.
Revise: Pyramids of BiomassExcess amino acids cannot be stored as protein indefinitely. Their nitrogen can leave an animal in urea in urine. This is excretion, not egestion, and it removes material that might otherwise have contributed to biomass.
The removal from an organism of waste products made by metabolism.
The removal of waste products made by the body’s cells.
For Higher Tier, keep the organs distinct: the liver deaminates excess amino acids and converts toxic ammonia to urea; the kidneys remove urea from the blood for excretion in urine.
Do not confuse excretion with egestion: excretion removes metabolic waste such as urea, whereas egestion removes undigested food.
Do not confuse egestion with excretion: faeces contain unabsorbed material, whereas urine contains excretory products such as urea and water.
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