IP Biology Notes: Excretion in Humans (Upper Sec 07)
26 Nov 2025, 00:00 Z
Reviewed by
Ezekiel Tan·Academic Advisor (Biology)
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Use this as a free IP Biology notes chapter on excretion in humans for Year 3 to Year 4. It keeps the IP pacing while reinforcing the 6093 biology foundations most schools test through DBQs, diagrams, and practical explanations.
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 (
