PhotosynthesisAQA A-Level Biology: Topic test

20 questions, 54 marks

AQA A-Level Biology

Photosynthesis topic test

Total 54 marks

Name

Class

Date

1
A researcher illuminates isolated chloroplasts and then adds a chemical that makes the thylakoid membranes freely permeable to protons. Electron transfer along the electron transfer chain carries on, but ATP production stops.
(a)
What is the most likely reason that ATP production stops?
[1 mark]
AChlorophyll can no longer absorb light.
BAn electrochemical gradient of protons can no longer be maintained across the thylakoid membrane.
CWater can no longer be split by photolysis.
DATP synthase has been removed from the membrane.
(b)
Which statement about the ATP synthase in a chloroplast is correct?
[1 mark]
AIt is found in the stroma and uses ATP to pump protons.
BIt is embedded in the thylakoid membrane and uses energy from electrons directly to join ADP and phosphate.
CIt is embedded in the thylakoid membrane and ATP is made as protons diffuse through it down their electrochemical gradient.
DIt is found in the outer membrane of the chloroplast and makes ATP by substrate-level phosphorylation.
(c)
Explain why reduced NADP is still produced in this experiment even though ATP is not.
[2 marks]
Total for question 1: 4 marks
2
Strawberry plants are grown in a polytunnel at a constant 25 °C, close to the optimum temperature for their enzymes. The light intensity is already high. The grower raises the carbon dioxide concentration in the tunnel from 0.04% to 0.10% and finds that the rate of photosynthesis rises.
(a)
Which factor was most likely limiting the rate of photosynthesis before the carbon dioxide concentration was raised?
[1 mark]
ALight intensity
BTemperature
CChlorophyll concentration
DCarbon dioxide concentration
(b)
Immediately after the carbon dioxide concentration is raised, how do the concentrations of GP and RuBP in the leaf change?
[1 mark]
AGP rises and RuBP falls
BGP falls and RuBP rises
CBoth rise
DBoth fall
(c)
Describe how the extra carbon dioxide is incorporated into the Calvin cycle.
[2 marks]
Total for question 2: 4 marks
3
A suspension of isolated chloroplasts is kept in bright light with plenty of carbon dioxide. In the Calvin cycle in these chloroplasts, 90 micromoles of carbon dioxide are fixed per minute. Each carbon dioxide fixed gives two molecules of GP, and reducing each molecule of GP to triose phosphate uses one molecule of reduced NADP and one molecule of ATP.
(a)
Calculate the rate, in micromoles per minute, at which reduced NADP is used to reduce GP in these chloroplasts. Show your working.
[3 marks]
(b)
The light is switched off. Explain why the concentration of GP rises and the concentration of RuBP falls.
[4 marks]
Total for question 3: 7 marks
4
Wheat plants in a field are exposed to drought. Their stomata close for most of the day. The light is bright and the temperature is suitable, so the wheat is not short of light.
(a)
Explain how closing the stomata affects the concentrations of RuBP and GP and the rate of the light-independent reaction.
[6 marks]
(b)
Explain why the rate of the light-dependent reaction also falls under these conditions, even though the light is bright.
[6 marks]
Total for question 4: 12 marks
5
A student separated the pigments in a spinach leaf extract by paper chromatography. The solvent front moved 9.0 cm from the start line. The carotene spot moved 8.1 cm and the chlorophyll b spot moved 4.5 cm.
(a)
What is the Rf value of chlorophyll b?
[1 mark]
A0.50
B0.56
C2.0
D0.90
(b)
Which statement best explains why carotene moves further up the paper than chlorophyll b?
[1 mark]
ACarotene is a larger molecule than chlorophyll b.
BCarotene absorbs more light than chlorophyll b.
CCarotene is attracted more strongly to the paper than chlorophyll b.
DCarotene is more soluble in the solvent and less strongly attracted to the paper.
(c)
Explain why the start line is drawn in pencil and why the extract spot must be above the level of the solvent.
[2 marks]
Total for question 5: 4 marks
6
Isolated chloroplasts were illuminated in water containing the heavy isotope oxygen-18 (H₂¹⁸O) and carbon dioxide containing only the common isotope oxygen-16. The oxygen gas released was collected and found to contain only oxygen-18.
(a)
What does this result show about the source of the oxygen released in photosynthesis?
[1 mark]
AIt comes from carbon dioxide.
BIt comes from water.
CIt comes from glucose.
DIt comes from RuBP.
(b)
Which pair are both products of the photolysis of water?
[1 mark]
AOxygen and ATP
BElectrons and reduced NADP
CProtons and oxygen
DGP and electrons
(c)
Explain the role of the electrons released by photolysis of water.
[2 marks]
Total for question 6: 4 marks
7
A glasshouse grower grows cucumbers with the air carbon dioxide concentration at the normal level and obtains a mean yield of 20.0 kg per plant. In a second, identical glasshouse she enriches the air with carbon dioxide and obtains a mean yield of 26.0 kg per plant. The enrichment costs £0.60 per plant and cucumbers sell for £1.50 per kg.
(a)
Calculate the percentage increase in yield caused by carbon dioxide enrichment, and the extra profit per plant after the cost of enrichment has been taken into account.
[3 marks]
(b)
Explain, in terms of the light-independent reaction, why the yield increased with enrichment. Suggest why a further rise in carbon dioxide concentration might not increase the yield any more.
[4 marks]
Total for question 7: 7 marks
8
Crop plants growing in soil short of magnesium ions have yellow-green leaves. The leaves contain much less chlorophyll than normal, and their rate of photosynthesis is lower than that of healthy plants at every light intensity.
(a)
Explain how the lower concentration of chlorophyll reduces the rate of the light-dependent reaction.
[6 marks]
(b)
A grower suggests supplying extra carbon dioxide to these plants. Predict the effect of the magnesium shortage on the concentrations of GP and RuBP in the leaves, and explain why extra carbon dioxide would not increase the yield.
[6 marks]
Total for question 8: 12 marks

End of questions

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).