Energy & respiration: A Level Biology questions with answers
Free Energy & respiration questions for A Level Biology (9700), part of Energy & control. Each question has the answer and the marking points an examiner would look for.
Anaerobic respiration in yeast and mammals produces different products.
(a)
Explain why anaerobic respiration produces much less ATP than aerobic respiration.
[2]
(b)
Explain why reduced NAD must be reoxidised in anaerobic conditions.
[2]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
only glycolysis; no ETC
only glycolysis occurs (2 ATP) B1 Krebs cycle and oxidative phosphorylation cannot occur without oxygen B1
2
(b)
NAD needed for glycolysis to continue
NAD is needed to accept hydrogen in glycolysis B1 so glycolysis can continue B1
2
Question 2Structured · 10 marksA* challenge
Germinating seeds in a respirometer take in 25 cm3 of oxygen and give out 14 cm3 of carbon dioxide in one hour.
(a)
Calculate the respiratory quotient and suggest the substrate being respired.
[2]
(b)
Describe how ATP is produced by oxidative phosphorylation.
[5]
(c)
Explain why the ATP yield from anaerobic respiration is much lower than from aerobic respiration.
[3]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
0.56; lipid
CO2 ÷ O2M1 0.56 with correct substrate A1
2
(b)
NADH/FADH2 deliver electrons to electron transport chain on inner membrane; energy used to pump H+ into intermembrane space; proton gradient; H+ diffuse back through ATP synthase (chemiosmosis); oxygen final electron acceptor forming water
reduced NAD/FAD donate electrons B1 electron carriers in inner membrane B1 protons pumped into intermembrane space B1 chemiosmosis through ATP synthase B1 oxygen as final acceptor B1
5
(c)
only glycolysis produces ATP (2 per glucose); no Krebs cycle or oxidative phosphorylation; NAD regenerated by producing lactate/ethanol
only glycolysis occurs B1 no electron transport chain/oxidative phosphorylation B1 NAD regenerated by lactate/ethanol pathway B1
3
Question 3Structured · 8 marks
A student uses a simple respirometer containing germinating peas and soda lime. The movement of coloured liquid in the capillary tube is recorded.
time / min
0
5
10
15
20
distance moved / cm
0.00
0.15
0.31
0.45
0.60
Table 3.1
(a)
Explain why the liquid moves towards the peas.
[2]
(b)
The capillary has a radius of 0.50 mm. Calculate the rate of oxygen uptake in mm³ min−1.
[3]
(c)
Describe a suitable control and explain its purpose.
[2]
(d)
Explain why the apparatus is kept in a water bath.
[1]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
O₂ used; CO₂ absorbed by soda lime; volume/pressure decreases
the peas take in oxygen for aerobic respiration B1 the carbon dioxide released is absorbed by soda lime, so the gas volume (pressure) inside decreases B1
2
(b)
0.236 mm³ min⁻¹
distance per minute = 0.300 mm M1 volume = πr2l = π × 0.502 × 0.300 M1 0.236 mm3 min−1A1
3
(c)
same apparatus with boiled peas / glass beads of same volume
identical tube with an equal volume of glass beads (or boiled peas) B1 shows changes in temperature or pressure not due to respiration B1
2
(d)
temperature affects gas volume and enzyme activity
temperature changes alter gas volume and the rate of respiration B1
1
Question 4Structured · 9 marks
Germinating seeds are placed in a respirometer at 25 °C. In 20 minutes they take in 1.80 cm³ of oxygen and give out 1.62 cm³ of carbon dioxide.
(a)
Define respiratory quotient (RQ).
[1]
(b)
Calculate the RQ of the seeds.
[1]
(c)
Use your answer to (b) to suggest the main respiratory substrate. Explain your answer.
[2]
(d)
Calculate the mean rate of oxygen uptake in cm³ per hour.
[1]
(e)
Explain why the respirometer contains potassium hydroxide solution when oxygen uptake is measured.
[2]
(f)
Describe how the same respirometer could be used to find the volume of carbon dioxide produced.
[2]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
CO₂ given out ÷ O₂ taken in
volume of carbon dioxide produced ÷ volume of oxygen used, in the same time B1
1
(b)
0.90
1.62 ÷ 1.80 = 0.90 B1
1
(c)
protein
protein B1 RQ of protein is about 0.9 B1
2
(d)
5.40 cm³ h−1
1.80 × 3 = 5.40 B1
1
(e)
absorbs CO₂; volume change due to O₂ only
KOH absorbs the carbon dioxide produced B1 so the change in volume is due only to oxygen taken in B1
2
(f)
repeat with water instead of KOH; difference = CO₂
repeat the experiment with water in place of potassium hydroxide (so CO₂ is not absorbed) B1 volume of CO₂ = volume of O₂ taken in (with KOH) − volume change without KOH B1
2
Question 5Structured · 5 marks
Aerobic respiration takes place in the cytoplasm and the mitochondria.
(a)
Describe the link reaction.
[3]
(b)
Explain the role of oxygen in oxidative phosphorylation.
[2]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
pyruvate decarboxylated and dehydrogenated; acetyl CoA
pyruvate enters the mitochondrion B1 it is decarboxylated (CO₂ removed) and dehydrogenated (reduced NAD formed) B1 acetyl group combines with coenzyme A B1
3
(b)
final electron acceptor; forms water
oxygen is the final electron acceptor B1 combines with electrons and protons to form water B1
2
Question 6Structured · 11 marks
This question is about glycolysis and the Krebs cycle.
(a)
State where glycolysis occurs and name the three-carbon compound produced at the end of it.
[2]
(b)
Outline the main stages of glycolysis.
[4]
(c)
Describe what happens to the acetyl group in the Krebs cycle.
[3]
(d)
The theoretical maximum yield is about 38 ATP per glucose, but the actual yield is about 30–32. Explain why it is less.
[2]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
cytoplasm; pyruvate
cytoplasm B1 pyruvate B1
2
(b)
glucose phosphorylated using 2 ATP; splits into 2 triose phosphate; TP oxidised, NAD reduced; 4 ATP made, net 2
glucose is phosphorylated using two ATP (hexose bisphosphate) B1 it splits into two triose phosphates B1 each triose phosphate is oxidised (dehydrogenated), reducing NAD B1 four ATP are made by substrate-linked phosphorylation, net gain of two B1
4
(c)
combines with oxaloacetate (4C) to form citrate (6C); decarboxylation and dehydrogenation; NAD, FAD reduced, ATP made
acetyl (2C) combines with oxaloacetate (4C) to form citrate (6C) B1 citrate is decarboxylated and dehydrogenated back to oxaloacetate B1 producing reduced NAD and FAD, CO₂ and one ATP per turn B1
3
(d)
some H⁺ leak; energy lost as heat; ATP used to transport pyruvate/ADP
some protons leak across the inner membrane B1 energy is used to transport pyruvate, ADP and phosphate into the mitochondrion / lost as heat B1
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Original Cambridge-style practice questions written for mentorriyaz.in. These are not Cambridge past paper questions, and this site is not affiliated with or endorsed by Cambridge University Press & Assessment. Updated 2026-11-04. Paper generator · mentorriyaz.in