mi4t/brainOKF v0.2
conceptstableVerified (1)by: deepseek-flash

Excretion

The removal of the waste products of metabolism and of substances in excess of requirements, chiefly carbon dioxide, urea, and surplus water and ions.

#excretion#kidney#urea#homeostasis#egestion#igcse-biology#biology

Excretion

Excretion is the removal of the waste products of metabolism and of substances in excess of requirements 1.

Excretory Products in Humans

ProductWhere it is producedRemoved by
Carbon dioxideRespiration in every cellLungs — excreted in exhaled air
UreaBreakdown of excess amino acids in the liverKidneys — excreted in urine
Excess water and ionsTaken in with food and drinkKidneys — excreted in urine

Urine passes from the kidneys down the ureters to the bladder and leaves through the urethra 1. Without excretion, urea and carbon dioxide would accumulate to toxic concentrations, so excretion is inseparable from homeostasis.

Excretion Is Not Egestion

Faeces are undigested food that never entered the body’s cells, so defecation is egestion, not excretion. Excretion covers only substances produced by reactions inside cells, plus harmless materials present in excess of requirements. In plants, waste gases leave the leaves by diffusion through the stomata.

  • Living Thing - Entity carrying out all seven life processes.
  • Organism - Individual living thing, unicellular or multicellular.
  • Respiration - Produces the carbon dioxide that must be excreted.
  • Nutrition - Supplies water, ions and amino acids in excess of requirements.
  • Sensitivity - Excretion is an effector output of homeostatic control.
  • Biology - Cambridge IGCSE life-science area.

Footnotes

  1. Cambridge IGCSE Biology 0610 syllabus for examination in 2026, 2027 and 2028 - Excretion (1.1f), excretion in humans and the kidneys, ureters, bladder and urethra (13.1). ↩ ↩2