Cambridge O Level Biology 5090: Respiration (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 10, Respiration, of the Cambridge O Level Biology 5090 syllabus for examination in 2026, 2027 and 2028 (version 4): every learning outcome in sections 10.1 Respiration, 10.2 Aerobic respiration and 10.3 Anaerobic respiration, including the investigation of temperature and respiration in yeast. 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 6, 7 and 9.

Questions

1. Describe what is meant by respiration. [2]

2. This question is about aerobic respiration.

(a) State the word equation for aerobic respiration. [2] (b) State the balanced chemical equation for aerobic respiration. [2]

3. Describe aerobic respiration. [2]

4. State the word equation for anaerobic respiration in:

(a) human muscle cells [1] (b) yeast. [2]

5. Compare aerobic respiration with anaerobic respiration in human muscle cells. [4]

6. Use the balanced equation for aerobic respiration to answer these.

(a) A liver cell respires 7 molecules of glucose aerobically. Calculate the number of oxygen molecules used. [1] (b) Calculate the number of carbon dioxide molecules released by the same cell. [1] (c) A root cell releases 54 molecules of water by aerobic respiration. Calculate the number of glucose molecules it respired. [1]

7. A student investigated the effect of temperature on respiration in yeast. She mixed yeast with glucose solution and placed equal volumes in five boiling tubes, each in a water-bath at a different temperature. She left the tubes for 10 minutes, then collected the gas released over water in an upturned measuring cylinder for 10 minutes.

Temperature / °C	15	25	35	45	55
Volume of gas in 10 min / cm³	3.0	8.0	15.0	11.0	2.0

(a) Calculate the rate of gas release at 35 °C, in cm³ per minute. [1] (b) Describe the results. [2] (c) Explain the results. [3] (d) State two variables, other than the volume of the mixture, that the student should keep the same. [2] (e) Suggest why the tubes were left in the water-baths for 10 minutes before the gas was collected. [1] (f) Suggest a control that would show the gas is released by living yeast. [1]

8. Explain why lactic acid builds up in the muscles and blood during vigorous exercise. [4]

9. An athlete’s resting oxygen uptake is 0.35 dm³ per minute. Her oxygen uptake was measured each minute after a 400 m race.

Minute after race	1	2	3	4	5	6	7
Oxygen uptake / dm³ per min	2.35	1.75	1.15	0.75	0.50	0.35	0.35

(a) Calculate the total extra oxygen she used after the race, above her resting uptake. [2] (b) State what the letters EPOC stand for. [1] (c) Outline how the oxygen debt is removed after exercise. [4] (d) Explain why her oxygen uptake had returned to 0.35 dm³ per minute by minute 6. [2]

10. A student boiled some glucose solution, cooled it to 30 °C and added yeast. She covered the mixture with a layer of oil and connected the flask by a delivery tube to a tube of limewater. After 20 minutes the limewater turned milky and the temperature in the flask had risen slightly.

(a) Suggest why the glucose solution was boiled and then covered with oil. [2] (b) Name the gas that turned the limewater milky. [1] (c) Name the other product of respiration that would be found in the flask. [1] (d) Suggest why the temperature in the flask rose. [1]

11. State the use of energy from respiration in each example.

(a) A root hair cell takes in nitrate ions from soil water where nitrate ions are less concentrated than in the cell. [1] (b) A ribosome joins amino acids together to make an enzyme. [1] (c) A message travels along a neurone from the skin to the spinal cord. [1] (d) A penguin keeps its body at about the same temperature in freezing weather. [1]

Answers

1. The chemical reactions in all living cells [1] that release energy from glucose [1]. [2] Examiner insight: “Respiration is breathing” or “respiration produces energy” contradicts the definition; use the words “chemical reactions”, “cells” and “release”.

2. (a) glucose + oxygen [1] → carbon dioxide + water [1] (b) Correct formulae C₆H₁₂O₆, O₂, CO₂ and H₂O [1]; balanced with 6O₂, 6CO₂ and 6H₂O [1]. [4] Examiner insight: Check the balance by counting oxygen atoms (18 on each side) before moving on; a missing 6 makes the equation unbalanced.

3. The release of a relatively large amount of energy [1] by the breakdown of glucose in the presence of oxygen [1]. [2] Examiner insight: “Uses oxygen” alone does not describe aerobic respiration; the amount of energy is a separate idea and needs “relatively large”.

4. (a) glucose → lactic acid [1] (b) glucose → ethanol [1] + carbon dioxide [1] [3] Examiner insight: Alcohol is another name for ethanol, but adding oxygen or water as a product makes the yeast equation wrong.

5. Any four [4]:

• aerobic uses oxygen; anaerobic does not use oxygen
• aerobic releases a relatively large amount of energy; anaerobic releases a relatively small amount
• aerobic produces carbon dioxide and water; anaerobic produces lactic acid
• anaerobic produces no carbon dioxide
• anaerobic leads to an oxygen debt after exercise; aerobic does not
• both break down glucose / both release energy [4] Examiner insight: A comparison needs both sides of each point; “anaerobic releases less energy” is clearer than a list of anaerobic facts with no reference to aerobic.

6. (a) 7 × 6 = 42 molecules [1] (b) 7 × 6 = 42 molecules [1] (c) 54 ÷ 6 = 9 molecules [1] [3] Examiner insight: Write the ratio (1 glucose : 6 oxygen : 6 carbon dioxide : 6 water) before calculating, so any error is easy to trace.

7. (a) 15.0 ÷ 10 = 1.5 cm³ per minute [1] (b) The volume of gas increases from 3.0 cm³ at 15 °C to a maximum of 15.0 cm³ at 35 °C [1]; it then decreases to 2.0 cm³ at 55 °C [1]. (c) Respiration is controlled by enzymes [1]. As temperature rises to 35 °C, molecules have more kinetic energy, so enzymes and substrates collide more often [1]. Above the optimum, the enzymes are denatured: the active site changes shape so the substrate no longer fits [1]. (d) Any two [2]: mass of yeast; concentration of glucose solution; collection time; size of tube; type of yeast. (e) So that the mixture reached the temperature of the water-bath [1]. (f) Repeat with boiled (killed) yeast, which should release no gas [1]. [10] Examiner insight: In (b) quote values with units, including the highest point; in (c) “the yeast died” is weaker than naming denatured enzymes and the active site.

8. Muscles contract hard and need energy very quickly [1]. Oxygen cannot be supplied to the muscles fast enough for aerobic respiration to release all of it [1]. So the muscles also respire anaerobically [1], producing lactic acid, which builds up in the muscles and passes into the blood [1]. [4] Examiner insight: “Not enough oxygen” needs to be linked to the rate of supply to the muscles; an answer that says the body has “run out of oxygen” is inaccurate.

9. (a) Subtract 0.35 from each value: 2.00, 1.40, 0.80, 0.40, 0.15, 0, 0 [1]; total = 4.75 dm³ [1] (b) Excess Post-exercise Oxygen Consumption [1] (c) Heart rate stays fast [1] to transport lactic acid in the blood from the muscles to the liver [1]. Breathing stays deeper and faster [1] to supply oxygen for the breakdown of lactic acid in the liver [1]. (d) All the lactic acid had been broken down, so the oxygen debt was repaid [1]; oxygen was now needed only for normal aerobic respiration at rest [1]. [9] Examiner insight: In (c) give a reason with each change; “breathing stays fast to get more energy” misses the lactic acid and liver link that the outcome asks for.

10. (a) Boiling removes dissolved oxygen [1]; the oil stops oxygen from the air dissolving back in, so the yeast respires anaerobically [1]. (b) Carbon dioxide [1] (c) Ethanol (alcohol) [1] (d) Respiration releases energy, and some of it is released as heat [1]. [5] Examiner insight: In (a) the oil has a different job from boiling; one reason stated twice in different words does not cover both.

11. (a) Active transport [1] (b) Protein synthesis [1] (c) Passage of electrical impulses along neurones [1] (d) Maintenance of a constant body temperature [1] [4] Examiner insight: Use the syllabus wording for each use; “moving ions” or “keeping warm” is too vague to name the process.

Where marks are usually lost

• Writing that respiration produces or makes energy.
• Treating respiration and breathing as the same thing.
• Putting carbon dioxide in the human anaerobic equation, or lactic acid in the yeast equation.
• Leaving the 6s out of the balanced equation, or writing oxygen as O.
• Describing yeast results without quoting the temperature and value of the highest rate.
• Explaining the fall above the optimum without the words “enzymes” and “denatured”.
• Vague controlled variables such as “same amount” with no quantity named.
• Saying lactic acid is broken down in the muscles, or that the heart beats fast after exercise “to get more energy”.
• Forgetting to subtract the resting value when calculating an oxygen debt.

Next steps

• Revision notes for this topic
• Study guide for this topic
• Enzymes practice questions
• Human gas exchange practice
• Cambridge O Level Biology course hub
• Printable checklist
• All 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 10: Respiration, published by Cambridge Assessment International Education.