A Level Biology (A2) chapter 2: Photosynthesis MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
48 exam-style questions on Photosynthesis, 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.
Photosynthesis as an energy transfer process30 questions
Investigation of limiting factors18 questions
Ten Photosynthesis questions with answers
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. Methylene blue can be used instead of DCPIP with a chloroplast suspension. In the light, which colour change shows that the light-dependent reactions are taking place?
A
colourless to blue, as it is oxidised
B
blue to colourless, as it is reduced
C
blue to colourless, as it is oxidised
D
colourless to blue, as it is reduced
Show answer
Answer: B. Like DCPIP, methylene blue is blue when oxidised and becomes colourless when it is reduced by electrons from the light-dependent reactions.
2. In a DCPIP experiment with a chloroplast suspension, which control shows that the colour change depends on light?
A
a tube with DCPIP and buffer but no chloroplasts
B
an identical tube containing boiled chloroplasts
C
a tube with chloroplasts and water instead of DCPIP
D
an identical tube wrapped in aluminium foil
Show answer
Answer: D. Only light is changed in the foil-wrapped tube, so if it stays blue, the reduction of DCPIP needs light. The boiled chloroplast tube tests whether active chloroplasts are needed.
3. Chloroplasts contain circular DNA and 70S ribosomes in the stroma. How does this relate to their function?
A
they let the chloroplast make some of its own proteins, such as part of rubisco
B
they allow photolysis of water to take place in the stroma
C
they store the sugars made in the Calvin cycle
D
they absorb light energy for the light-dependent stage
Show answer
Answer: A. Chloroplast DNA codes for some chloroplast proteins, including part of rubisco, which are made on the 70S ribosomes in the stroma. Photolysis happens in the thylakoids.
4. In bright light with plenty of carbon dioxide, the rate of photosynthesis falls sharply above about 40 °C. What is the main reason?
A
the carbon dioxide concentration of the air falls at high temperature
B
chlorophyll molecules absorb less light as they warm up above 40 °C
C
more oxygen dissolves in the leaf cells, inhibiting photolysis
D
enzymes such as rubisco begin to lose their tertiary structure
Show answer
Answer: D. Above the optimum, bonds holding the tertiary structure of enzymes such as rubisco break, active sites change shape and the Calvin cycle slows. Light absorption by pigments is hardly affected by temperature.
5. In an investigation of the effect of light intensity on photosynthesis in pondweed, a glass tank of water is placed between the lamp and the plant. Why?
A
to reduce the light intensity to a level that the plant is able to use
B
to filter out the green light, which would slow the rate of photosynthesis
C
to supply extra carbon dioxide to the plant
D
to absorb heat from the lamp so that the temperature stays constant
Show answer
Answer: D. As the lamp is moved closer it also heats the plant; the water absorbs much of this heat, so temperature does not change along with light intensity.
6. In the Calvin cycle, where are ATP and reduced NADP used?
A
reduced NADP and ATP both only in regenerating RuBP
B
reduced NADP in reducing GP to TP; ATP in reducing GP and in regenerating RuBP
C
ATP in fixing carbon dioxide; reduced NADP in regenerating RuBP
D
reduced NADP in fixing carbon dioxide with RuBP; ATP only in reducing GP to TP
Show answer
Answer: B. The reduction of GP to triose phosphate needs both ATP and reduced NADP. Regenerating RuBP from triose phosphate needs ATP only. Carbon fixation by rubisco needs neither.
7. For every six molecules of carbon dioxide fixed in the Calvin cycle, how many molecules of triose phosphate are formed, and how many of these are used to regenerate RuBP?
A
12 formed; 10 used to regenerate RuBP
B
6 formed; 5 used to regenerate RuBP
C
12 formed; 2 used to regenerate RuBP
D
12 formed; 6 used to regenerate RuBP
Show answer
Answer: A. Six CO2 + six RuBP give 12 GP, reduced to 12 triose phosphate (36 carbon atoms). Six RuBP (30 carbon atoms) need 10 triose phosphate, leaving 2 (6 carbon atoms), enough for one hexose.
8. Tubes of chloroplast suspension with DCPIP were lit through coloured filters giving light of equal intensity. Time for the blue colour to disappear: red light 90 s, blue light 110 s, green light 600 s. A tube with DCPIP and buffer but no chloroplasts, in white light, stayed blue. Which conclusion is correct?
A
green light drives the light-dependent reactions fastest of the three colours
B
DCPIP is reduced by light alone, even when no chloroplasts at all are present
C
the Calvin cycle runs fastest in red light
D
red and blue light drive the light-dependent stage faster than green light
Show answer
Answer: D. Faster decolorisation means faster electron flow in the light-dependent stage, which uses red and blue light absorbed by chlorophyll. The tube without chloroplasts rules out light alone reducing DCPIP, and DCPIP measures the light-dependent stage, not the Calvin cycle.
9. Why is measuring the volume of gas in a capillary tube more reliable than counting bubbles from pondweed?
A
bubbles vary in size, so a count does not measure volume accurately
B
counting bubbles also includes the carbon dioxide released by the pondweed
C
bubbles from pondweed contain only nitrogen gas released from the water
D
measuring the volume of gas removes the need to control the temperature
Show answer
Answer: A. Bubble size varies with light intensity and from one bubble to the next, so equal numbers of bubbles need not mean equal volumes of oxygen. Temperature must still be controlled.
10. The volume of gas collected from an aquatic plant in bright light is used to measure its rate of photosynthesis. Why does this underestimate the true rate?
A
some oxygen is used in the plant's respiration or dissolves in the water
B
the gas collected also contains some carbon dioxide made in photosynthesis
C
the lamp heats the water, which destroys some of the oxygen
D
the sodium hydrogencarbonate absorbs some of the oxygen
Show answer
Answer: A. The gas measured is the net oxygen released: some oxygen produced is used in the plant's own respiration and some dissolves in the water. Photosynthesis uses carbon dioxide rather than producing it.
48, each with the answer and a short explanation, across 2 topics: Photosynthesis as an energy transfer process, Investigation of limiting factors. Every chapter test draws ten of them, so you can take it many times.
Is the A Level Biology (A2) chapter 2 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.
