Free Photosynthesis questions for IGCSE Biology (0610), part of Plant nutrition. Each question has the answer and the marking points an examiner would look for.
Generate a full Photosynthesis worksheet →All Plant nutrition questionsAt the compensation point, which is true?
Answer: C
Which is the balanced chemical equation for photosynthesis?
Answer: B
A plant is kept in the dark for 48 hours before a starch test. Why?
Answer: C
Photosynthesis takes place in the chloroplasts of leaf cells.
Write the word equation for photosynthesis.
Describe the role of chlorophyll.
State two uses of the glucose made in photosynthesis.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | carbon dioxide + water → glucose + oxygen (light, chlorophyll) carbon dioxide + water → glucose + oxygen B1 in the presence of light and chlorophyll B1 | 2 |
| (b) | absorbs light energy absorbs light energy (to make it available for photosynthesis) B1 | 1 |
| (c) | respiration; starch; cellulose; sucrose Any 2 of: respiration; stored as starch; cellulose for cell walls; converted to sucrose for transport B2 | 2 |
A student investigates the effect of light intensity on the rate of photosynthesis of a water plant by counting the bubbles of gas released per minute. Fig. 5.1 shows the results.
Describe the effect of light intensity on the rate of photosynthesis shown in Fig. 5.1.
Use Fig. 5.1 to find the rate of photosynthesis at a light intensity of 35 units.
Calculate the percentage increase in the rate when the light intensity increases from 20 to 50 units.
Suggest which factor limits the rate of photosynthesis at light intensities above 80 units. Explain your answer.
State two variables, other than light intensity, that the student should keep constant.
Suggest why counting bubbles may not give an accurate measure of the rate of photosynthesis.
Write the balanced chemical equation for photosynthesis.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | rate increases then levels off rate increases as light intensity increases (up to about 50–60 units) B1 then levels off / stays constant (allow data quote) B1 | 2 |
| (b) | 25 bubbles per minute 25 ± 1 bubble per minute B1 | 1 |
| (c) | 45 % (27.5 − 19) ÷ 19 × 100 C1 45 % (allow ± 5 %, ft their readings) A1 | 2 |
| (d) | carbon dioxide concentration / temperature carbon dioxide concentration / temperature B1 increasing light intensity has little or no further effect on the rate (the curve levels off), so light is no longer the limiting factor B1 | 2 |
| (e) | temperature; CO₂ concentration; plant / species; time Any 2 of: temperature; carbon dioxide (hydrogencarbonate) concentration; same plant / length of plant; time of counting B2 | 2 |
| (f) | bubbles different sizes; some O₂ used in respiration / dissolves Any 2 of: bubbles are not all the same size / volume; some oxygen is used in respiration or dissolves in the water; bubbles hard to count at high rates B2 | 2 |
| (g) | 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ correct formulae B1 balanced (light and chlorophyll may be written over the arrow) B1 | 2 |
A student places a piece of pondweed in water at different distances from a lamp and counts the bubbles released in one minute.
| distance from lamp / cm | 10 | 20 | 30 | 40 | 50 |
|---|---|---|---|---|---|
| bubbles per minute | 50 | 50 | 33 | 19 | 12 |
Write the balanced chemical equation for photosynthesis.
Name the gas in the bubbles.
Describe and explain the effect of distance from the lamp on the rate of photosynthesis.
At 10 cm the rate does not increase further. Suggest which factor is limiting the rate at this distance, and explain.
State two variables the student should keep constant.
Explain why counting bubbles is not an accurate way to measure the rate of photosynthesis, and suggest a better method.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ correct formulae B1 balanced B1 | 2 |
| (b) | oxygen oxygen B1 | 1 |
| (c) | closer lamp, more bubbles; higher light intensity; light is the limiting factor Any 3 of: as distance increases the number of bubbles decreases; light intensity decreases with distance; light is the limiting factor; data quote B3 | 3 |
| (d) | carbon dioxide concentration or temperature carbon dioxide concentration / temperature B1 increasing light no longer increases the rate so another factor is in short supply B1 | 2 |
| (e) | temperature; CO₂ concentration; same pondweed; time Any 2 of: temperature (use a water bath / heat filter); carbon dioxide concentration (add same mass of hydrogen carbonate); same piece of pondweed; same counting time B2 | 2 |
| (f) | bubbles vary in size; collect gas in a syringe / measure volume bubbles are of different sizes / some oxygen dissolves B1 collect the gas in a gas syringe / capillary tube and measure its volume B1 | 2 |
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Meet Riyaz →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