O Level / IGCSE Biology chapter 6: Plant nutrition MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
33 exam-style questions on Plant nutrition, 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. On a bright winter day the temperature in a greenhouse is 5 °C and the carbon dioxide concentration is high. Which change would most increase the rate of photosynthesis?
A
adding extra lamps to raise the light intensity above that of the Sun
B
increasing the humidity so that the stomata stay open for longer
C
shading the plants to reduce water loss on the bright day
D
raising the temperature with heaters
Show answer
Answer: D. Light and carbon dioxide are already plentiful, but 5 °C is too cold for the enzymes to work quickly, so temperature is the limiting factor. Raising it increases the rate.
2. A plant with variegated leaves (green and white areas) is destarched and then left in light for 6 hours. A leaf is tested with iodine solution. What is the result?
A
only the green areas turn blue-black; the white areas stay orange-brown
B
the whole leaf turns blue-black, because starch is made in all the leaf cells
C
only the white areas turn blue-black, because they cannot use up the starch
D
the whole leaf stays orange-brown, because no starch is made in six hours
Show answer
Answer: A. Only the green areas contain chlorophyll, so only they photosynthesise and make starch that turns blue-black with iodine. The white areas have no chlorophyll and give no starch.
3. Why do plants store carbohydrate as starch rather than as glucose?
A
starch is carried in the xylem, so it can be moved to the roots
B
starch dissolves easily in the cytoplasm, so it can be moved to where it is needed
C
starch is insoluble, so it does not affect the water potential of cells
D
starch is used to build cell walls, so the plant grows taller
Show answer
Answer: C. Starch is insoluble, so large amounts can be stored without changing the water potential of the cell and drawing in water by osmosis. Glucose is soluble.
4. Why is a plant kept in the dark for 48 hours before an experiment on photosynthesis?
A
to stop the plant respiring so that no carbon dioxide is released in the dark
B
to use up the starch already in the leaves, so that any starch found is new
C
to increase the amount of chlorophyll in the leaves before the experiment
D
to open the stomata so the leaves are ready to take in carbon dioxide
Show answer
Answer: B. Keeping the plant in the dark uses up the starch stored in its leaves, so that any starch found after the experiment was made during it. The plant still respires in the dark.
5. Most leaves are thin. How does this help photosynthesis?
A
it gives a short diffusion distance for carbon dioxide to reach the cells
B
it lets the leaf store more water in the cells for use in photosynthesis
C
it stops the leaf from wilting by keeping the cells close to the xylem
D
it allows the leaf to hold more stomata on its upper surface for gas exchange
Show answer
Answer: A. A thin leaf means carbon dioxide has only a short distance to diffuse from the stomata to the photosynthesising cells, and light can reach all the cells.
6. Why does magnesium deficiency reduce the growth of a plant?
A
the plant wilts, because water cannot move up the xylem vessels
B
the roots die, so the plant cannot absorb water and mineral ions
C
less chlorophyll is made, so less light is absorbed for photosynthesis
D
fewer proteins are made, so the plant cannot form new cells and enzymes
Show answer
Answer: C. Magnesium is part of chlorophyll. With less chlorophyll the leaves absorb less light, so less glucose is made and growth is reduced.
7. What is the role of chlorophyll in photosynthesis?
A
it transfers light energy into chemical energy for making glucose
B
it stores the glucose that has been made as starch in the chloroplast
C
it controls the opening and closing of the stomata during the day
D
it takes in carbon dioxide through the stomata for use in the leaf
Show answer
Answer: A. Chlorophyll absorbs light and transfers its energy to the chemical energy needed to make glucose. Guard cells control stomata, and carbon dioxide diffuses in through the stomata.
8. Where is chlorophyll found in a leaf cell?
A
in the cell wall
B
in the chloroplasts
C
in the sap vacuole
D
in the mitochondria
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Answer: B. Chlorophyll is a green pigment inside chloroplasts. Mitochondria are for respiration.
9. A student counts the bubbles released by a piece of pondweed. With a lamp 10 cm away, 45 bubbles are released in 5 minutes. With the lamp 20 cm away, 18 bubbles are released in 3 minutes. By what percentage did the rate of bubble release fall?
A
33%
B
3%
C
67%
D
50%
Show answer
Answer: A. Rate at 10 cm = 45 ÷ 5 = 9 bubbles per minute. Rate at 20 cm = 18 ÷ 3 = 6 bubbles per minute. The fall is 3 ÷ 9 × 100 = 33%. The rates must be compared per minute, not as totals.
10. What is the word equation for photosynthesis?
A
glucose + oxygen → carbon dioxide + water
B
carbon dioxide + oxygen → glucose + water
C
carbon dioxide + water → glucose + oxygen
D
water + oxygen → glucose + carbon dioxide
Show answer
Answer: C. Carbon dioxide and water are the raw materials; glucose and oxygen are the products, with light and chlorophyll needed. Glucose + oxygen as reactants is respiration, the reverse process.
33, each with the answer and a short explanation, across 3 topics: Photosynthesis, Leaf structure, Mineral nutrition. Every chapter test draws ten of them, so you can take it many times.
Is the O Level / IGCSE Biology chapter 6 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.
