IP Biology Notes: Excretion in Humans (Upper Sec 07)
Free IP Biology notes on kidney structure, urine formation, and dialysis basics for Sec 3 to Sec 4.
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.
The core idea is simple: Excretion removes metabolic waste from the body.
Use it as a working check: Do not confuse excretion with egestion. Kidneys remove urea, excess salts, and excess water by ultrafiltration and selective reabsorption.
Then go one layer deeper: Example: glucose is small enough to enter the filtrate, but a healthy nephron reabsorbs it in the proximal convoluted tubule so it does not appear in urine.
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).
