IGCSE Biology (0610)
The kidney and excretion
What this topic tests, the mistakes that cost marks, and one exam-style question worked through step by step.
Key ideas and common mistakes
- Excretion specifically refers to removing metabolic waste produced inside the body, not undigested food or substances that never entered the body's cells.Common mistake: Students often confuse excretion with egestion.
- The liver is the organ where absorbed amino acids are both used to build new proteins and where surplus amino acids are broken down (deaminated).Common mistake: Students often confuse this with the small intestine, where absorption occurs, or the kidneys, which excrete waste.
- Urea is produced in the liver during deamination, not in the kidneys or blood, so confusing its site of formation with where it is filtered or excreted is a common error.
- Identifying the kidney as the organ that filters urea from the blood and produces urine.Common mistake: Not confusing it with organs that process or store urine (like the bladder) or detoxify blood (like the liver).
- Link each excretory organ to the metabolic waste it removes: the lungs remove carbon dioxide made by respiration, while the kidneys remove urea.
- Identifying that the main nitrogen-containing waste product formed from deamination of amino acids in the liver and transported in blood to the kidneys is urea, not ammonia or another nitrogenous compound.
Worked example
Describe the meaning of the biological term excretion.
Try it first, then show the working
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Any 2 of these:removal / getting rid of waste products of metabolism / metabolic waste · toxic materials AND/OR substances present in excess of the body's requirements / carbon dioxide from respiration · waste is made inside the body cells (distinguishes excretion from egestion)
Answer: Excretion is the removal from the body of the waste products of metabolism (such as urea and carbon dioxide), together with toxic materials and substances in excess of requirements.
Try one yourself
State the name of this organ.Answer it and get it marked →
State where in the body urea is made.Answer it and get it marked →
State which organ removes urea from the blood.Answer it and get it marked →
16 exam-style questions on The kidney and excretion, each marked to the scheme.
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Questions are exam-style practice written to the IGCSE Biology (0610) syllabus. Cambridge IGCSE is a registered trademark of Cambridge University Press & Assessment; MOOBON Axiom is independent and not affiliated with it.