O Level / IGCSE Biology chapter 13: Excretion MCQs with answers

By Team Megalecture · Updated 4 Nov 2026

20 exam-style questions on Excretion, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.

20 questions · 2 topics · 10 per test

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What chapter 13 covers

Ten Excretion questions with answers

Try each one, then open the answer. These ten stay the same; the test draws new ones every time.

1. Through which organ is carbon dioxide excreted?

  1. A
    the kidneys
  2. B
    the liver
  3. C
    the lungs
  4. D
    the skin
Show answer

Answer: C. Carbon dioxide from respiration diffuses from the blood into the alveoli and is breathed out.

2. In which order does fluid pass through these parts of the urinary system as urine is formed and leaves the kidney?

  1. A
    Bowman's capsule, loop of Henle, collecting duct, ureter
  2. B
    Bowman's capsule, collecting duct, loop of Henle, ureter
  3. C
    Bowman's capsule, loop of Henle, ureter, collecting duct
  4. D
    loop of Henle, Bowman's capsule, collecting duct, ureter
Show answer

Answer: A. Filtrate enters the Bowman's capsule, flows along the tubule and loop of Henle to a collecting duct, and the urine then leaves the kidney down the ureter.

3. A stone blocks the tube that leads from one kidney to the bladder. Which tube is blocked?

  1. A
    collecting duct
  2. B
    ureter
  3. C
    renal vein
  4. D
    urethra
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Answer: B. Each ureter carries urine from a kidney to the bladder. The urethra carries urine from the bladder out of the body.

4. Which row correctly states where urea is made and which organ removes it from the blood?

  1. A
    made in the liver, removed by the lungs
  2. B
    made in the liver, removed by the kidneys
  3. C
    made in the kidneys, removed by the liver
  4. D
    made in the pancreas, removed by the kidneys
Show answer

Answer: B. Urea is made in the liver from the breakdown of excess amino acids. The kidneys filter it out of the blood and excrete it in the urine.

5. In a nephron, which structure is a tight knot of blood capillaries where blood is filtered?

  1. A
    collecting duct
  2. B
    loop of Henle
  3. C
    Bowman's capsule
  4. D
    glomerulus
Show answer

Answer: D. The glomerulus is a tangle of capillaries where blood is filtered into the surrounding Bowman's capsule.

6. What is deamination?

  1. A
    the breakdown of glucose to release energy in cells
  2. B
    removal of the nitrogen-containing part of excess amino acids in the liver
  3. C
    the joining of amino acids to make proteins in the liver
  4. D
    the removal of water from urine in the collecting ducts
Show answer

Answer: B. Deamination removes the nitrogen part of excess amino acids; this is converted to urea and the rest can be used for energy.

7. The concentration of urea is 0.03 g per 100 cm3 in blood plasma and 2.0 g per 100 cm3 in urine. About how many times more concentrated is urea in the urine?

  1. A
    6.7
  2. B
    67
  3. C
    0.015
  4. D
    200
Show answer

Answer: B. 2.0 ÷ 0.03 = 66.7, about 67 times. The kidney concentrates urea by reabsorbing most of the water.

8. Which of these is a waste product of metabolism?

  1. A
    fibre
  2. B
    urea
  3. C
    glucose
  4. D
    amino acids
Show answer

Answer: B. Urea is made from excess amino acids. Fibre is undigested food; glucose and amino acids are useful nutrients.

9. Why must urea be excreted?

  1. A
    it is needed to make more urine and keep the bladder full
  2. B
    it is useful to the kidneys, which store it as an energy reserve
  3. C
    it is toxic, so it would harm the cells if it built up in the blood
  4. D
    it would be converted into glucose and raise blood sugar
Show answer

Answer: C. Urea is toxic at high concentration, so it must be removed from the blood.

10. What is excretion?

  1. A
    the removal of undigested food and bacteria from the alimentary canal
  2. B
    the release of hormones and enzymes from glands into the blood
  3. C
    the loss of water and heat from the skin in order to cool the body
  4. D
    removal of toxic materials and waste products of metabolism from the body
Show answer

Answer: D. Excretion removes substances made by the body's own metabolism. Removing undigested food is egestion.

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Excretion: questions students ask

How many Excretion MCQs are there?

20, each with the answer and a short explanation, across 2 topics: Excretion, Urinary system. Every chapter test draws ten of them, so you can take it many times.

Is the O Level / IGCSE Biology chapter 13 test free?

Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.

How is the chapter test marked?

The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.

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