Explain why photosynthesis is described as an endothermic reaction.

AQA GCSE Biology (8461) — 4.4.1 Photosynthesis · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Plants carry out photosynthesis to produce food. Carbon dioxide and water are converted into glucose and oxygen during this process.

Model answer (4 marks)

Photosynthesis is endothermic because it absorbs energy from the environment.
1. Light energy is taken in by the chloroplasts.
2. This energy is used to convert CO₂ and H₂O into glucose and O₂.
3. The reaction therefore requires an energy input.
4. The absorbed energy is stored in the chemical bonds of glucose.

Examiner tips

Use the word 'absorb' or 'take in' to show energy input.
Mention light as the energy source.
Explain that the energy is stored in glucose.
Keep the answer concise and use correct terminology.

Common mistakes

Saying photosynthesis releases energy instead of absorbs it.
Confusing exothermic with endothermic.
Omitting the role of light as the energy source.

Mark scheme (4 marks)

Energy is transferred/absorbed FROM the environment (into the chloroplasts/plant)
The energy is transferred by light
In an endothermic reaction, energy is taken in / the reaction requires an energy input
The energy is transferred to the chloroplasts

Key terms in this question

photosynthesis · endothermic