GCSE Biology · Edexcel 1BI0 · Topic 6A
Photosynthesis
Key points
- Photosynthesis: carbon dioxide + water → glucose + oxygen, using light energy absorbed by chlorophyll in chloroplasts.
- It is endothermic because it takes in energy from light. Plants are producers, making food for whole food chains.
- Limiting factors: light intensity, carbon dioxide concentration and temperature. Whichever factor is in shortest supply limits the rate.
- Core practical: use pondweed and count oxygen bubbles (or measure gas volume) with a lamp at different distances.
- Inverse square law: light intensity , so doubling the distance gives a quarter of the light intensity.
- Glucose is used for respiration, or turned into starch (storage), cellulose (cell walls) and proteins.
- Higher tier: interpret graphs where a line levels off because another factor becomes limiting.
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Photosynthesis is how plants and algae use light energy to make glucose. This sub-topic covers the reaction, the factors that limit its rate and the core practical that measures it with pondweed.
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