This guide covers IGCSE Biology topic 13: excretion in humans. You will revise excretion (removal of waste), the kidneys (filtration, reabsorption, urine), the nephron, and the skin (sweat: water, salts, urea).

Key concepts to revise

• Excretion – Removal of waste products of metabolism (e.g. urea, CO2). Not the same as egestion (faeces).
• Kidneys – Filter blood; remove urea, excess water and salts; form urine. Know the role of filtration and reabsorption.
• Nephron – Filtration in glomerulus; reabsorption of useful substances (glucose, water, salts) in tubule; urine to bladder.
• Skin – Sweat glands excrete water, salts and a little urea; cooling by evaporation.

Exam tips and command words

• State – What excretion is; what the kidneys excrete (urea, excess water, salts).
• Describe – The path of urine (kidney to ureter to bladder to urethra); filtration and reabsorption in the nephron.
• Explain – Why reabsorption is needed (glucose and salts are useful; water balance).
• Label – Kidney (cortex, medulla, ureter); nephron (glomerulus, tubule).

Common mistakes

• Confusing excretion (urea, CO2) with egestion (faeces; undigested food).
• Saying the kidney produces urine without mentioning filtration and reabsorption.
• Not stating that glomerulus filters and tubule reabsorbs.

Revision checklist

• Define excretion and name the main excretory products (urea, CO2) and where they are removed.
• Describe the role of the kidney (filtration, reabsorption, urine formation).
• Label a diagram of the kidney and nephron; state the function of glomerulus and tubule.
• State what sweat contains and the role of skin in excretion and temperature regulation.

Next steps

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