Edexcel International GCSE Biology 4BI1: Excretion – 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 sub-topic 2(i), Excretion (specification points 2.70–2.79), of the Pearson Edexcel International GCSE Biology (4BI1) specification, Issue 3. The qualification is untiered. Questions 1 and 2 test points 2.70 and 2.71, which can be examined on either paper. Questions labelled (Paper 2 only) test the bold B points 2.72B–2.79B. The set applies to the June and November series examined under Issue 3. A calculator may be used throughout, as in both 4BI1 papers.

Learn the content first with the excretion study guide and the excretion revision notes. The course hub is Edexcel IGCSE Biology and every specification point is on the printable checklist. For other Topic 2 practice, try the cell structure practice questions.

Questions

1. State one excretory product of each organ.

(a) Lungs [1] (b) Kidneys [1] (c) Skin [1]

2. Plants make waste gases but have no excretory organs.

(a) Name the process that makes oxygen as a waste product in a leaf. [1] (b) Explain why a leaf in bright light gives out oxygen but takes in carbon dioxide. [3]

3. (Paper 2 only) Name the structure of the urinary system that:

(a) carries urine from a kidney to the bladder [1] (b) stores urine [1] (c) carries urine out of the body [1] (d) carries blood into a kidney. [1]

4. (Paper 2 only) These are parts of a nephron: collecting duct, Bowman’s capsule, loop of Henle, distal convoluted tubule, proximal convoluted tubule.

(a) Write the parts in the order that filtrate passes through them. [2] (b) Name the knot of blood capillaries inside Bowman’s capsule. [1] (c) Name the part of the nephron that makes the tissue of the medulla concentrated. [1]

5. (Paper 2 only) Describe how glomerular filtrate is formed, and explain why it contains no red blood cells. [4]

6. (Paper 2 only) The table shows the concentrations of three substances in fluid from different places in a person’s kidney, in g per dm³.

Substance	Blood plasma	Glomerular filtrate	Urine
Glucose	0.9	0.9	0
Amino acids	0.5	0.5	0
Urea	0.30	0.30	18.0

(a) Name the process that produces glomerular filtrate. [1] (b) Name the part of the nephron where the glucose concentration falls to zero, and give one reason why the body reabsorbs glucose. [2] (c) Calculate how many times more concentrated urea is in urine than in the filtrate. [2] (d) Explain why the concentration of urea is higher in urine than in the filtrate. [2]

7. (Paper 2 only) In one person, glomerular filtrate is formed at 120 cm³ per minute and urine is produced at 1.5 cm³ per minute.

(a) Calculate the volume of filtrate formed in one day. Give your answer in dm³. [2] (b) Calculate the percentage of the filtrate volume that is reabsorbed into the blood. Give your answer to one decimal place. [2] (c) Explain how water is reabsorbed into the blood from the collecting duct. [3]

8. (Paper 2 only) A runner sweats heavily on a hot day and does not drink. Describe how ADH changes the volume and concentration of the runner’s urine. [5]

9. (Paper 2 only) The cells lining the proximal convoluted tubule have many mitochondria and many microvilli.

(a) Explain how each feature helps these cells reabsorb glucose. [4] (b) A person’s blood glucose concentration is very high. Suggest why glucose is found in their urine. [2]

10. (Paper 2 only) A small mammal from a desert has much longer loops of Henle than a similar mammal from a wet habitat. Suggest how its longer loops help it survive in the desert. [3]

11. (Paper 2 only) Describe the path of a urea molecule from the renal artery to outside the body, and explain why the concentration of urea in the fluid rises along the way. [8]

12. (Paper 2 only) A urine test shows that a person’s urine contains protein. Suggest which part of the nephron is damaged, and explain your answer. [3]

Answers

1. (a) Carbon dioxide (accept water vapour) [1] (b) Urea (accept water or ions/salts; do not accept urine) [1] (c) Water, ions (salts) or urea, in sweat [1] Examiner insight: Each organ is a separate mark, and “urine” for the kidneys is a product made of several substances, so a mark scheme usually asks for a named substance such as urea.

2. (a) Photosynthesis [1] (b) In bright light the rate of photosynthesis is greater than the rate of respiration [1]; so more oxygen is made than is used, and the extra oxygen diffuses out through the stomata [1]; carbon dioxide is used faster than respiration makes it, so more diffuses in through the stomata [1] Examiner insight: “Plants photosynthesise in the day and respire at night” loses the first mark – respiration happens all the time, and the mark is for comparing the two rates.

3. (a) Ureter [1] (b) Bladder [1] (c) Urethra [1] (d) Renal artery [1] Examiner insight: Spelling that could be either ureter or urethra (for example “urether”) is not credited, because the two words name different structures.

4. (a) Bowman’s capsule → proximal convoluted tubule [1]; → loop of Henle → distal convoluted tubule → collecting duct [1] (b) Glomerulus [1] (c) Loop of Henle [1] Examiner insight: In (a), “first” and “second” convoluted tubule are accepted in place of proximal and distal, but the two must not be swapped.

5. The blood vessel entering the glomerulus is wider than the vessel leaving it, so blood pressure in the glomerulus is high [1]; small molecules (water, glucose, urea, ions) are forced out of the capillaries into Bowman’s capsule [1]; this is ultrafiltration [1]; red blood cells are too large to pass through the capillary wall and capsule wall, so they stay in the blood [1] Examiner insight: “High pressure” alone is not enough for the first mark – you need to say where the pressure is (the glomerulus) or why it is high.

6. (a) Ultrafiltration [1] (b) Proximal convoluted tubule [1]; glucose is needed for respiration (as a source of energy) [1] (c) 18.0 ÷ 0.30 [1] = 60 times [1] (d) Water is reabsorbed from the filtrate (in the collecting duct) [1]; urea is not reabsorbed, so the same mass of urea is in a smaller volume of water [1] Examiner insight: In (d), “urea is added to the urine” is a common wrong idea and earns no credit; the marks are for water leaving and urea staying.

7. (a) 120 × 60 × 24 = 172 800 cm³ [1]; ÷ 1000 = 172.8 dm³ [1] (b) (120 − 1.5) ÷ 120 × 100 [1] = 98.8% [1] (c) The loop of Henle makes the tissue of the medulla concentrated (high ion concentration) [1]; water moves out of the collecting duct by osmosis into the medulla [1]; and then into the blood capillaries [1] Examiner insight: In (a), an answer of 172 800 with no unit change keeps the method mark only; the final answer must be in the unit the question asks for.

8. Water lost in sweat lowers the water content of the blood [1]; this is detected by the brain (hypothalamus) [1]; the pituitary gland releases more ADH [1]; ADH makes the walls of the collecting duct more permeable to water, so more water is reabsorbed into the blood [1]; so a small volume of concentrated urine is produced [1] Examiner insight: The last mark needs both volume and concentration, because the question asks about both.

9. (a) Mitochondria carry out respiration, releasing energy [1]; this energy is needed for active transport of glucose into the cells [1]; microvilli give a large surface area [1]; so glucose is reabsorbed faster [1] (b) There is more glucose in the filtrate than the tubule can reabsorb [1]; so the glucose that is not reabsorbed stays in the filtrate and passes into the urine [1] Examiner insight: “Mitochondria make energy” is not credited – energy is released (or transferred) by respiration, not made.

10. Longer loops make the tissue of the medulla more concentrated [1]; so more water is reabsorbed by osmosis from the collecting ducts [1]; so the mammal makes a small volume of very concentrated urine and conserves water [1] Examiner insight: In a “suggest” question, credit goes to a linked chain of reasoning; “it saves water” on its own, without the mechanism, scores at most one mark.

11. Urea is carried in the plasma to the glomerulus [1]; high pressure forces urea into Bowman’s capsule by ultrafiltration [1]; urea is a small molecule, so it passes through the filter [1]; it moves along the proximal convoluted tubule, loop of Henle and distal convoluted tubule [1]; urea is not reabsorbed into the blood [1]; water is reabsorbed by osmosis (especially from the collecting duct), so urea concentration rises [1]; urine passes from the collecting duct to the ureter and into the bladder [1]; it is stored in the bladder and leaves the body through the urethra [1] Examiner insight: Extended answers are marked on separate creditworthy points, so a path that skips the ureter or names it in the wrong place loses that point even if the rest is correct.

12. The glomerulus (or Bowman’s capsule) is damaged [1]; proteins are normally too large to pass out of the glomerulus into the filtrate [1]; damage lets protein pass into the filtrate, and it then passes into the urine [1] Examiner insight: Naming a tubule (for example the collecting duct) scores no marks here, because the explanation marks depend on linking the protein to filtration.

Where marks are usually lost

• Writing “plants respire only at night” instead of comparing the rates of photosynthesis and respiration.
• Answering “urine” when asked for an excretory product of the kidneys.
• Mixing up ureter and urethra, or renal artery and renal vein.
• Swapping the proximal and distal convoluted tubules.
• Explaining ultrafiltration without saying why the pressure in the glomerulus is high.
• Writing “urea is added” or “urea is made in the kidney” to explain the high urea concentration in urine.
• Stating “ADH reabsorbs water” rather than “ADH makes the collecting duct more permeable to water”.
• Leaving a volume calculation in cm³ when dm³ is asked for, or dividing by the urine volume in a percentage reabsorbed calculation.
• Writing “mitochondria make energy”.

Next steps

• Revise with the excretion revision notes.
• Re-read any weak sections in the excretion study guide.
• See the full course on the Edexcel IGCSE Biology hub and tick off points on the printable checklist.
• Try all free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

Pearson Edexcel International GCSE in Biology (4BI1) specification, Issue 3 (first assessment June 2019), published by Pearson Education Limited. These questions cover Topic 2, sub-topic (i) Excretion, points 2.70–2.79B.