GCSE Biology: Photosynthesis
Photosynthesis is the anchor of the bioenergetics topic, and GCSE papers test it from three angles: the reaction itself, the factors limiting its rate, and what the plant does with the glucose. This quiz covers all three.
The reaction questions secure the fundamentals — the word equation (carbon dioxide + water → glucose + oxygen), the fact that photosynthesis is endothermic, and its location in the chloroplasts. The limiting factors questions then do the heavier lifting: identifying light intensity, carbon dioxide concentration and temperature as the three primary limiting factors, explaining why rate falls at high temperature (enzyme denaturation, connecting back to the enzymes topic), and interpreting the classic rate graph — where a plateau means light is no longer the limiting factor because something else has taken over, the single most-tested graph interpretation in the topic. The inverse square law question (Higher tier only) makes the quantitative link: doubling the distance from a lamp cuts light intensity to a quarter.
The glucose questions complete the picture with the five uses the specification lists: respiration, storage as starch, producing fats and oils, building cellulose for cell walls, and combining with nitrate ions to make amino acids for proteins. Two follow-up questions push into the reasoning layer — why starch (insoluble, osmotically inert) beats glucose as a storage molecule, and which use is structural.
Every question is self-contained with a full explanation, and the flashcards drill the equations and factor list — legitimate recall here, since biology equations are not provided on any exam sheet.
- State the word and symbol equations for photosynthesis and its endothermic nature
- Identify light, CO₂ and temperature as limiting factors and explain the temperature effect via enzymes
- Interpret rate graphs, including what a plateau means
- Apply the inverse square law linking light intensity and distance (Higher tier)
- List the five uses of glucose and explain why starch is the storage form
Topic scope follows the bioenergetics section of the Department for Education's GCSE combined science subject content: the photosynthesis reaction, the effect of limiting factors on rate, and the uses of glucose in plants.
Sample question
The graph shows the rate of photosynthesis against light intensity. What does the plateau at the end of the curve indicate?
- The plant has died.
- Another factor, such as temperature or CO2 concentration, has become the limiting factor.
- The light intensity is too high and has damaged the plant.
- The plant has stopped producing oxygen.
See the answer
Another factor, such as temperature or CO2 concentration, has become the limiting factor.
When the rate of photosynthesis plateaus, it means that increasing the light intensity further no longer increases the rate because another factor (like CO2 or temperature) is now limiting the process.
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