IGCSE Biology Topic 13: Excretion in Humans MCQs – 30 Practice Questions with Answers (Cambridge 0610)
Free practice for Cambridge IGCSE Biology 0610 on excretion in humans, covering the excretory organs, the kidney and the nephron, with every question followed by a worked explanation.
What Excretion Is and Which Organs Carry It Out
Q1. Which statement best describes excretion?
- (A) The removal of undigested food from the gut
- (B) The removal of metabolic waste products and substances in excess of requirements
- (C) The breakdown of large food molecules into small soluble molecules during digestion in the gut
- (D) The movement of digested food into the blood
Show Answer
Answer: B – Excretion removes waste made by metabolism, plus substances the body has in excess, rather than undigested food or digested nutrients.
Q2. Which waste product is excreted through the lungs?
- (A) Urea, which is carried in the blood to the kidneys for removal
- (B) Excess salts
- (C) Glucose
- (D) Carbon dioxide
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Answer: D – Carbon dioxide, produced by respiration, leaves the blood in the lungs and is breathed out.
Q3. Which substances do the kidneys excrete?
- (A) Urea and excess water and ions
- (B) Carbon dioxide and excess water only
- (C) Glucose and amino acids
- (D) Undigested fibre and bile
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Answer: A – The kidneys remove urea from the blood together with water and ions that are present in excess.
Q4. How does egestion differ from excretion?
- (A) Egestion removes urea formed in the liver, while excretion removes carbon dioxide produced by respiration in the lungs
- (B) Egestion takes place in the kidneys, while excretion takes place in the gut
- (C) Egestion removes undigested food that never entered the body cells, while excretion removes metabolic waste
- (D) Egestion and excretion are two names for exactly the same process
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Answer: C – Undigested food passing out of the gut is egestion, because it was never absorbed into the cells, whereas excretion deals with waste from metabolism.
Q5. In which organ is urea formed?
- (A) The kidney
- (B) The liver
- (C) The bladder
- (D) The pancreas
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Answer: B – Urea is formed in the liver from excess amino acids, and the kidneys then remove it from the blood.
Q6. What happens during deamination?
- (A) The nitrogen-containing part of an amino acid is removed to form urea
- (B) Glucose is converted into glycogen for storage in the liver and muscles when blood glucose is high
- (C) Urea is broken down into amino acids
- (D) Proteins are digested into fatty acids
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Answer: A – Deamination strips the nitrogen-containing part from excess amino acids, and that nitrogen ends up in urea.
Q7. Why is excretion important in the human body?
- (A) It supplies the cells with extra glucose
- (B) It increases the volume of blood in circulation by adding extra water absorbed from the gut
- (C) It converts waste products back into useful proteins
- (D) It prevents toxic substances such as urea from building up in the body
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Answer: D – Urea is toxic, so it must be removed rather than allowed to accumulate in the blood and tissues.
Q8. Which role does the liver play in the assimilation of amino acids?
- (A) It stores amino acids unchanged in the gall bladder
- (B) It filters amino acids out of the urine
- (C) It converts amino acids into proteins the body needs
- (D) It breaks amino acids down into carbon dioxide and water that are then excreted through the lungs
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Answer: C – In assimilation, the liver uses absorbed amino acids to build new proteins for growth and repair.
Q9. In a diagram of a kidney section, which region lies on the outside?
- (A) The cortex
- (B) The ureter
- (C) The bladder wall
- (D) The renal vein
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Answer: A – The cortex is the outer region of the kidney, while the medulla lies beneath it.
Q10. What is the function of the ureters?
- (A) They filter the blood in the kidney
- (B) They carry urine from the kidneys to the bladder
- (C) They store urine until it leaves the body through the urethra at a suitable time
- (D) They produce urea in the liver
Show Answer
Answer: B – Each ureter is a tube that transports urine from a kidney down to the bladder.
The Kidney and the Nephron
Q11. Which pair of structures correctly matches storage with release of urine?
- (A) Ureter stores urine and the kidney releases it
- (B) Bladder filters blood and the urethra stores urine until it is released from the body
- (C) Kidney stores urine and the bladder filters blood
- (D) Bladder stores urine and the urethra carries it out of the body
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Answer: D – Urine collects in the bladder and leaves the body through the urethra.
Q12. What is filtered out of the blood in the glomerulus?
- (A) Blood cells and large plasma proteins only
- (B) Urea alone, with all other substances kept in the blood
- (C) Water, glucose, urea and ions
- (D) Glycogen and undigested food particles
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Answer: C – Filtration in the glomerulus passes small molecules, including water, glucose, urea and ions, out of the blood.
Q13. Which statement about filtration in the glomerulus is correct?
- (A) Filtration is not selective, so useful and waste substances pass out together
- (B) Filtration returns all the glucose directly to the blood without any need for reabsorption later
- (C) Filtration only allows urea to leave the blood
- (D) Filtration takes place in the bladder, not the kidney
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Answer: A – Filtration does not pick and choose, which is why useful substances must later be reabsorbed in the nephron.
Q14. During reabsorption in the nephron, what returns to the blood?
- (A) All of the urea and none of the water, leaving a large volume of very dilute fluid behind
- (B) All of the glucose, some of the ions and most of the water
- (C) All of the ions and none of the glucose
- (D) Blood cells and plasma proteins
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Answer: B – Reabsorption is selective: it recovers all the glucose, some ions and most of the water, while urea largely stays behind.
Q15. What does urine formed in the nephron contain?
- (A) Glucose, blood cells and plasma proteins
- (B) Amino acids and glycogen
- (C) Urea, excess water and excess ions
- (D) Carbon dioxide and undigested food
Show Answer
Answer: C – After filtration and reabsorption, what remains is urine containing urea plus water and ions in excess.
Q16. What is the role of the blood vessels associated with the nephron?
- (A) They carry urine from the nephron to the bladder for storage until it leaves the body
- (B) They supply the kidney with oxygen only
- (C) They filter glucose out of the urine
- (D) They carry reabsorbed substances back into the blood
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Answer: D – Capillaries around the nephron pick up the glucose, ions and water that are reabsorbed and return them to the circulation.
Q17. If reabsorption of glucose failed in a nephron, what would most likely be found in the urine?
- (A) Glucose
- (B) Blood cells
- (C) Glycogen
- (D) Plasma proteins
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Answer: A – Glucose is normally fully reabsorbed, so failure of that step would leave glucose in the fluid that becomes urine.
Q18. In addition to the kidneys and lungs, which organ contributes to excretion through sweat?
- (A) The liver
- (B) The pancreas
- (C) The skin
- (D) The spleen
Show Answer
Answer: C – Sweat released through the skin carries water and salts out of the body.
Q19. Why can excess amino acids not simply be stored for later use?
- (A) Amino acids dissolve in urine and are lost immediately
- (B) Excess amino acids are deaminated in the liver, with the nitrogen removed as urea
- (C) Amino acids are converted into glucose in the kidney and then released back into the blood
- (D) Amino acids are excreted unchanged through the lungs
Show Answer
Answer: B – The body has no store for surplus amino acids, so the liver deaminates them and the nitrogen is excreted as urea.
Q20. A person drinks very little water on a hot day. What is the likely effect on their urine?
- (A) A large volume of very dilute urine
- (B) Urine containing glucose
- (C) Urine with no urea at all
- (D) A smaller volume of more concentrated urine
Show Answer
Answer: D – When water is scarce, more water is reabsorbed in the nephron, so less, more concentrated urine is produced.
Putting the System Together
Q21. Which statement correctly links the liver and the kidneys in urea handling?
- (A) The liver forms urea and the kidneys remove it from the blood
- (B) The kidneys form urea and the liver removes it from the blood
- (C) The liver and the kidneys both form urea independently
- (D) The liver stores urea and the kidneys convert it to protein
Show Answer
Answer: A – Urea production happens in the liver, while removal from the blood is the kidneys’ job.
Q22. Which sequence correctly follows fluid through the excretory system?
- (A) Bladder, urethra, kidney, ureter
- (B) Ureter, glomerulus, nephron, bladder
- (C) Glomerulus filtration, nephron reabsorption, bladder storage, urethra release
- (D) Nephron filtration, liver deamination, lung excretion, bladder storage
Show Answer
Answer: C – Blood is filtered in the glomerulus, useful substances are reabsorbed in the nephron, urine is stored in the bladder and released through the urethra.
Q23. Why would a build-up of urea harm the body?
- (A) Urea blocks the absorption of food in the gut
- (B) Urea is toxic and disturbs the normal working of cells if it accumulates
- (C) Urea prevents the lungs from taking in oxygen
- (D) Urea turns into glucose and raises blood sugar sharply
Show Answer
Answer: B – The syllabus states the importance of excretion in terms of the toxicity of urea, so its accumulation disrupts cell function.
Q24. When kidneys fail, dialysis is used. What does dialysis do?
- (A) It repairs damaged nephrons inside the kidney
- (B) It replaces the liver’s role in making urea
- (C) It increases the amount of glucose in the blood
- (D) It filters the blood artificially to remove waste substances
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Answer: D – Dialysis stands in for the filtering work of failed kidneys by cleaning the blood outside the body.
Q25. How does a kidney transplant differ from dialysis?
- (A) A transplant replaces the organ itself, while dialysis only filters the blood artificially
- (B) A transplant filters blood outside the body, while dialysis works inside the kidney
- (C) A transplant removes the liver, while dialysis removes the bladder
- (D) A transplant and dialysis both repair the original nephrons
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Answer: A – Transplantation provides a working kidney, whereas dialysis is an artificial substitute for its filtering function.
Q26. A student claims that sweating is the body’s main way of removing urea. What is wrong with this claim?
- (A) Sweat contains no water at all
- (B) Sweat is produced only by the kidneys
- (C) Sweat mainly removes water and salts, while urea is mainly removed by the kidneys in urine
- (D) Sweating only happens when a person is asleep
Show Answer
Answer: C – The skin loses salts in sweat, but urea excretion is principally the kidneys’ work.
Q27. If both kidneys stopped filtering blood, which change would be expected first in the blood?
- (A) A sharp fall in carbon dioxide levels
- (B) A build-up of urea in the blood
- (C) A complete loss of glucose from the blood
- (D) A build-up of undigested food in the blood
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Answer: B – Without filtration, urea that the liver keeps forming would no longer be removed and would accumulate.
Q28. Which of the following is NOT an example of excretion?
- (A) Carbon dioxide leaving through the lungs
- (B) Urea leaving in urine
- (C) Salts leaving in sweat
- (D) Undigested food leaving through the anus
Show Answer
Answer: D – Passing out undigested food is egestion, not excretion, because the material never entered the body cells.
Q29. What drives filtration in the glomerulus?
- (A) Blood pressure forcing small molecules out of the blood
- (B) Muscles squeezing the bladder
- (C) Active transport of blood cells into the nephron
- (D) Diffusion of urea from the bladder back into the blood
Show Answer
Answer: A – High pressure in the glomerular capillaries pushes water, glucose, urea and ions out of the blood into the nephron.
Q30. Which summary best captures why excretion matters for the internal environment?
- (A) It adds nutrients to the blood after every meal
- (B) It stores excess water for use on hot days
- (C) It removes toxic waste and excess substances so conditions inside the body stay suitable for cells
- (D) It converts all waste products back into food molecules
Show Answer
Answer: C – By clearing urea and excess water and ions, excretion keeps the internal environment within limits cells can tolerate.
Revisit any questions you missed, especially filtration versus reabsorption, and practise tracing urea from the liver to the urine.