Photosynthesis: Reaction, Reactants and Products — AQA GCSE Biology
Photosynthesis is how plants and algae make their own food using light energy.
The reaction
Photosynthesis takes place in chloroplasts, which contain the green pigment chlorophyll that absorbs light. It is an endothermic reaction — energy is transferred from the environment (light) to the chloroplasts.
Word equation: carbon dioxide + water → glucose + oxygen
Symbol equation: $$6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$$ (in the presence of light and chlorophyll)
Reactants and products
- Reactants: carbon dioxide (from the air, via stomata) and water (from the soil, via roots).
- Products: glucose (used by the plant) and oxygen (released as a by-product).
Endothermic process
Because it takes in energy from light, photosynthesis is endothermic — the opposite of respiration, which is exothermic.
Exam tips
- Learn the word and symbol equations.
- Photosynthesis is endothermic (takes in light energy).
- Name the reactants (CO₂ and water) and products (glucose and oxygen).
- It happens in chloroplasts, using chlorophyll to absorb light.