GCSE Biology · AQA 8461 · Topic 4.4.1
Photosynthesis
Key points
- Word equation: carbon dioxide + water → glucose + oxygen (light energy, chlorophyll). Symbol equation: .
- Photosynthesis is endothermic: energy is transferred from the environment (as light) to the chloroplasts.
- Limiting factors: light intensity, CO concentration, temperature, and amount of chlorophyll. The factor in shortest supply limits the rate.
- Higher tier: light intensity follows the inverse square law, , so halving the distance makes it four times as bright.
- Glucose is used for respiration, converted to starch for storage, cellulose for cell walls, fats/oils for storage and amino acids (with nitrate ions) for proteins.
- Growers use greenhouses, lamps, heaters and extra CO, but only when the extra yield is worth the cost.
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Photosynthesis is how plants and algae make their own food, and it is the source of almost all the biomass on Earth. You need its equations, the factors that limit its rate, and how growers use this knowledge.
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