O Level / IGCSE Biology chapter 10: Respiration MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
26 exam-style questions on Respiration, 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.
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. Hydrogencarbonate indicator is red; it turns yellow when carbon dioxide increases and purple when it decreases. Maggots are kept above red indicator in a sealed tube in the dark for one hour. What colour does the indicator become?
A
colourless, because the maggots use up all of the indicator
B
yellow, because the maggots respire and release carbon dioxide
C
red, because the maggots do not respire when there is no light
D
purple, because the maggots absorb carbon dioxide in the dark
Show answer
Answer: B. Maggots respire, releasing carbon dioxide into the tube, so the indicator turns yellow. Animals respire in the dark and in the light.
2. What is the word equation for anaerobic respiration in human muscles?
A
glucose → ethanol + carbon dioxide
B
glucose → lactic acid
C
glucose + oxygen → lactic acid
D
glucose → lactic acid + carbon dioxide
Show answer
Answer: B. In human muscle, glucose is converted to lactic acid only; no carbon dioxide is produced. Ethanol and carbon dioxide are produced by yeast.
3. In an investigation of the effect of temperature on respiration in yeast, what is the dependent variable?
A
the concentration of sugar solution in each flask
B
the mass of yeast added to each flask
C
the volume of carbon dioxide produced
D
the temperature at which each flask is kept
Show answer
Answer: C. The dependent variable is what is measured as a result of changing the independent variable (temperature). Here it is the volume of carbon dioxide produced. The mass of yeast and sugar concentration are kept constant.
4. Why does lactic acid build up in the muscles during a sprint?
A
lactic acid is made from the oxygen that is breathed in faster during a sprint
B
the liver makes lactic acid and sends it to the muscles for use as fuel
C
the muscles stop respiring altogether, so lactic acid is made from the waste
D
oxygen cannot reach the muscles fast enough, so some glucose is respired anaerobically
Show answer
Answer: D. In a sprint the muscles need energy faster than oxygen can be supplied, so some glucose is broken down anaerobically, producing lactic acid which builds up.
5. What is the balanced chemical equation for aerobic respiration?
A
C6H12O6 + O2 → CO2 + H2O
B
6CO2 + 6H2O → C6H12O6 + 6O2
C
C6H12O6 + 6O2 → 6CO2 + 6H2O
D
C6H12O6 + 6O2 → 6CO2 + 12H2O
Show answer
Answer: C. One glucose reacts with six oxygen to give six carbon dioxide and six water: 18 oxygen atoms on each side.
6. Why does anaerobic respiration release less energy than aerobic respiration from the same amount of glucose?
A
the energy for the reaction comes from oxygen, which is absent
B
glucose is only partly broken down, so energy remains in the products
C
less glucose is used in the cell because oxygen is needed to take it up
D
the energy released is all lost as heat because there is no oxygen to hold it
Show answer
Answer: B. Anaerobic respiration breaks glucose down only partly, into lactic acid or ethanol, which still contain much chemical energy. Aerobic respiration breaks it down completely to carbon dioxide and water.
7. Which substance is a product of anaerobic respiration in yeast but not in human muscle?
A
urea, made in the liver
B
water, made by the mitochondria
C
lactic acid, made in the muscle fibres
D
carbon dioxide
Show answer
Answer: D. Yeast makes ethanol and carbon dioxide; human muscle makes lactic acid only. Carbon dioxide is therefore the product of anaerobic respiration in yeast but not in muscle.
8. What is the word equation for aerobic respiration?
A
carbon dioxide + water → glucose + oxygen
B
glucose + oxygen → carbon dioxide + water
C
glucose → lactic acid
D
glucose → ethanol + carbon dioxide
Show answer
Answer: B. Aerobic respiration uses glucose and oxygen and produces carbon dioxide and water. Carbon dioxide + water as reactants is photosynthesis.
9. Which substances are products of aerobic respiration?
A
lactic acid only
B
ethanol and carbon dioxide
C
glucose and oxygen
D
carbon dioxide and water
Show answer
Answer: D. Aerobic respiration produces carbon dioxide and water. Lactic acid and ethanol come from anaerobic respiration.
10. Yeast in sugar solution releases carbon dioxide at different temperatures. In 10 minutes it releases 3 cm3 at 5 °C, 12 cm3 at 20 °C, 30 cm3 at 35 °C and none at 80 °C. How many times faster is the mean rate at 35 °C than at 20 °C?
A
1.5 times
B
0.4 times
C
3 times
D
2.5 times
Show answer
Answer: D. Both are measured over 10 minutes, so the rates compare as 30 ÷ 12 = 2.5. At 80 °C the enzymes are denatured, so the yeast releases no carbon dioxide.
26, each with the answer and a short explanation, across 3 topics: Respiration, Aerobic respiration, Anaerobic respiration. Every chapter test draws ten of them, so you can take it many times.
Is the O Level / IGCSE Biology chapter 10 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.
