IP Biology Upper Sec 07: Excretion in Humans
Download printable cheat-sheet (CC-BY 4.0)26 Nov 2025, 00:00 Z
Join our Telegram study groupThese notes align with SEAB GCE O-Level Biology (6093) content used in IP programmes (exams from 2026).
Status: SEAB O-Level Biology 6093 syllabus (exams from 2026) checked 2025-11-30 - scope unchanged; remains the reference for this note.
What you must know
- Excretion = removal of metabolic waste (, urea, excess salts/water), not egestion. Main organs: lungs, kidneys, skin.
- Nephron: renal artery → afferent arteriole → glomerulus → Bowman’s capsule (ultrafiltration of small molecules) → proximal convoluted tubule (glucose, amino acids, most water/salts reabsorbed) → loop of Henle (water/salt), distal tubule (ion balance), collecting duct (water).
- Selective reabsorption uses diffusion, osmosis, and active transport (glucose reabsorbed fully in PCT).
- Kidney failure support: dialysis (diffusion across partially permeable membrane) or transplant.
Detailed notes
- Excretion vs egestion: metabolic wastes made in cells (




