Cambridge O Level Biology 5090: Excretion (5090) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover Topic 13, Excretion, of the Cambridge O Level Biology 5090 syllabus for examination in 2026, 2027 and 2028 (version 4): every learning outcome in sections 13.1 Excretion (13.1.1 to 13.1.3) and 13.2 Urinary system (13.2.1 to 13.2.6). The syllabus is not tiered, so every question applies to every candidate.

Revise first with the study guide and the revision notes. The course hub and the printable checklist list the other topics, and the free 10-minute diagnostics help you decide what to revise next. A calculator is useful for questions 5, 7, 8 and 11. All data in these questions are given values for the calculation, not reference figures to learn.

Questions

1. Define the term excretion. [2]

2. A diagram of the human urinary system shows two organs at the back of the abdomen, a narrow tube leaving each one, a muscular bag low in the abdomen, and a single tube leading from the bag to the outside.

(a) Name the narrow tube leaving each organ at the back of the abdomen. [1] (b) Name the muscular bag and state its function. [1] (c) State the function of the single tube leading to the outside. [1] (d) State the function of the kidneys. [1]

3. This question is about carbon dioxide.

(a) Name the process in cells that produces carbon dioxide as a waste product. [1] (b) Describe how carbon dioxide made in a leg muscle cell is removed from the body. [3]

4. The liver handles amino acids that arrive from the small intestine.

(a) Describe the role of the liver in the assimilation of amino acids. [2] (b) Describe what happens to an amino acid during deamination. [2] (c) Name the blood vessel that carries urea away from the liver. [1]

5. A man’s kidneys stop working. His blood urea concentration is 0.30 g/dm³ on day 0 and 1.2 g/dm³ on day 4.

(a) Calculate the percentage increase in his blood urea concentration. [2] (b) Explain why the urea concentration in his blood increases. [2] (c) Explain why the increase is a danger to him. [1]

6. This question is about the structure of a nephron.

(a) Name the knot of capillaries in which blood is filtered. [1] (b) Name the part of the nephron that surrounds this knot of capillaries. [1] (c) After leaving the part named in (b), fluid passes along a coiled tubule. Apart from further tubules, name, in order, the two structures it passes through before reaching the ureter. [2] (d) State where substances go when they are reabsorbed from the tubules. [1]

7. The table shows the concentrations of some substances in three fluids from a healthy person.

Substance	Blood plasma / g per dm³	Filtrate in Bowman’s capsule / g per dm³	Urine / g per dm³
Protein	70	0	0
Glucose	1.0	1.0	0
Urea	0.3	0.3	20

(a) Explain why protein is found in the plasma but not in the filtrate. [2] (b) Explain why glucose is in the filtrate but not in the urine. [2] (c) Calculate how many times more concentrated urea is in urine than in filtrate. Give your answer to one decimal place. [1] (d) Explain why urea is more concentrated in urine than in filtrate. [2]

8. In one person, filtrate is formed in the kidneys at 125 cm³ per minute and urine is produced at 1.0 cm³ per minute. Treat both volumes as water.

(a) Calculate the volume of filtrate formed in one hour, in dm³. [2] (b) Calculate the percentage of the filtered water that is reabsorbed. Give your answer to one decimal place. [2] (c) Calculate the volume of urine produced in 24 hours, in dm³. [1]

9. A nitrogen atom is part of a protein molecule in an egg that a girl eats. Her body does not need the amino acid that contains this atom. Describe the route of the nitrogen atom, and the processes that act on it, from the egg until it leaves her body. [8]

10. A student lists substances that leave the human body.

(a) State whether each is removed by excretion or by egestion: (i) urea, (ii) fibre, (iii) carbon dioxide. [3] (b) Explain why the removal of fibre is not excretion. [1]

11. A woman eats a low-protein diet for one week and then a high-protein diet for one week. On the last day of each week, the total mass of urea in her urine is measured.

Diet	Mass of urea in urine in one day / g
Low-protein	12
High-protein	30

(a) Calculate the percentage increase in the mass of urea excreted. [2] (b) Explain why more urea is excreted on the high-protein diet. [4] (c) Her urine contained no glucose on either diet. Explain why. [2] (d) Suggest one variable, other than the length of each diet, that should be kept the same for a fair comparison. [1]

Answers

1. The removal of toxic materials [1] and the waste products of metabolism from organisms [1]. [2] Examiner insight: “Getting rid of waste” alone is too vague for credit; the second mark depends on saying the waste comes from metabolism (reactions in cells).

2. (a) Ureter [1] (b) Bladder; stores urine [1] (c) Carries urine from the bladder out of the body [1] (d) Removes urea and excess salts and water from the blood, as urine [1] [4] Examiner insight: Ureter and urethra differ by a few letters, so a spelling that could be read as either word risks losing the mark; write the word carefully.

3. (a) (Aerobic) respiration [1] (b) Carbon dioxide diffuses out of the muscle cell into the blood plasma [1]; it is carried in the blood to the lungs [1]; it diffuses into the alveoli and is breathed out [1]. [4] Examiner insight: “Breathed out” alone earns only the last point; a description needs each stage of the route, with the organ (lungs) named.

4. (a) Liver cells take up amino acids [1] and convert (build) them into proteins, such as plasma proteins [1]. (b) The nitrogen-containing part of the amino acid is removed [1] and converted into urea [1]. (c) Hepatic vein [1] [5] Examiner insight: For (b), “the amino acid is broken down” does not say which part is removed; name the nitrogen-containing part to gain the first mark.

5. (a) (1.2 − 0.30) ÷ 0.30 × 100 [1] = 300% [1] (b) The liver continues to make urea by deaminating excess amino acids [1], but the kidneys no longer remove urea from the blood, so it accumulates [1]. (c) Urea is toxic, so a high concentration damages cells [1]. [5] Examiner insight: Dividing the increase by the final value (giving 75%) is a common slip; percentage increase is always divided by the starting value, and showing the expression can still earn the method mark.

6. (a) Glomerulus [1] (b) Bowman’s capsule [1] (c) Loop of Henle [1], then collecting duct [1] (d) Back into the blood, in the capillaries around the tubules [1] [5] Examiner insight: In (c) the order is part of the answer; collecting duct before loop of Henle is not credited as a correct sequence.

7. (a) Protein molecules are too large [1] to be filtered out of the blood at the glomerulus, so they stay in the blood [1]. (b) Glucose is filtered at the glomerulus [1]; all of it is reabsorbed into the blood (along the nephron), so none is left in urine [1]. (c) 20 ÷ 0.3 = 66.7 times [1] (d) Most of the water is reabsorbed [1] but urea is not reabsorbed, so the same urea is in a smaller volume of water [1]. [7] Examiner insight: In (b), saying “glucose is not filtered” contradicts the data in the table and earns nothing; the table shows glucose in the filtrate, so the answer must use reabsorption.

8. (a) 125 × 60 = 7500 cm³ [1] = 7.5 dm³ [1] (b) (125 − 1.0) ÷ 125 × 100 [1] = 99.2% [1] (c) 1.0 × 60 × 24 = 1440 cm³ = 1.44 dm³ [1] [5] Examiner insight: A unit conversion step (cm³ to dm³, divide by 1000) is often where an otherwise correct answer goes wrong; check the unit the question asks for before writing the final value.

9. Any eight of the points below, in a sensible order, 1 mark each [8]:

• Protein is digested by protease to amino acids;
• in the stomach and small intestine;
• amino acids are absorbed into the blood in the small intestine;
• carried to the liver in the hepatic portal vein;
• the excess amino acid is deaminated in the liver;
• the nitrogen-containing part is removed and made into urea;
• urea is carried in the blood plasma (via the hepatic vein and the circulation) to the kidneys in the renal artery;
• urea is filtered out of the blood at the glomerulus into the Bowman’s capsule;
• urea is not reabsorbed and passes along the tubules and collecting duct;
• it leaves in urine, through the ureter to the bladder;
• and out of the body through the urethra. [8] Examiner insight: In a long “describe the route” answer, each named place and each named process is a separate point; an answer that only lists organs without processes (digestion, absorption, deamination, filtration) is unlikely to reach full credit.

10. (a) (i) Excretion [1] (ii) Egestion [1] (iii) Excretion [1] (b) Fibre is undigested food that was never absorbed or made by metabolism in cells, so it is not a metabolic waste product [1]. [4] Examiner insight: Part (b) needs the link to metabolism; “because it comes out in faeces” restates egestion without explaining why it is not excretion.

11. (a) (30 − 12) ÷ 12 × 100 [1] = 150% [1] (b) More protein is digested, so more amino acids are absorbed [1]. The body needs only a limited amount for making proteins and cannot store the excess [1]. More excess amino acids are deaminated in the liver [1], so more urea is made and excreted by the kidneys [1]. (c) Glucose is filtered at the glomerulus [1] but all of it is reabsorbed into the blood [1]. (d) Any one [1]: same total volume of water drunk each day; same total energy intake; same level of physical activity; urine collected over the same 24-hour period. [9] Examiner insight: For (b), an answer that jumps from “more protein” straight to “more urea” misses the middle steps; the liver and deamination must appear to earn the central marks.

Where marks are usually lost

• Writing that the kidneys make urea; the liver makes it and the kidneys excrete it.
• Including faeces or fibre as an excretory product.
• Swapping ureter and urethra, or spelling them ambiguously.
• Saying glucose is not filtered, when a data table clearly shows it in the filtrate.
• Saying all of the water, or all of the ions, is reabsorbed.
• Describing deamination without naming the nitrogen-containing part.
• Giving the order of nephron parts incorrectly, especially placing the collecting duct before the loop of Henle.
• Leaving out units, or the cm³ to dm³ conversion, in calculations.
• Answering “why is excretion needed” with “to remove waste” instead of “urea is toxic”.

Next steps

• Recap with the revision notes.
• Reread any section you found hard in the study guide.
• Link this topic back to Human nutrition and Human gas exchange.
• See every topic on the course hub and tick off outcomes on the printable checklist.
• Try the free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

Cambridge O Level Biology 5090 syllabus for examination in 2026, 2027 and 2028 (version 4), Topic 13: Excretion (13.1 Excretion; 13.2 Urinary system), published by Cambridge Assessment International Education.