Explain why photosynthesis is described as an endothermic reaction and explain how the products of photosynthesis are used by a plant.

Edexcel GCSE Biology (1BI0) — 6.1 Photosynthesis · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Photosynthesis is endothermic because it requires an input of energy to drive the reactions; the light energy absorbed by chlorophyll is used to split water and reduce carbon dioxide.

The absorbed light energy is stored as chemical energy in the bonds of glucose.

Glucose is then used by the plant in cellular respiration to release energy for growth and maintenance.

It is also converted into other macromolecules such as cellulose for cell walls, starch for storage, and proteins for structural and enzymatic functions.

Examiner tips

  • Use the term "endothermic" and mention energy input from light. Show the conversion of light to chemical energy. Explain both respiration and biomass synthesis. Keep each point brief but complete.

Common mistakes

  • Saying photosynthesis releases energy (exothermic). Forgetting to mention the role of glucose in respiration. Mixing up the direction of energy flow (light to glucose, glucose to ATP).

Mark scheme (4 marks)

  1. Photosynthesis requires/takes in energy (from light)
  2. Light energy is converted into / stored as chemical energy (in glucose)
  3. Glucose is used in respiration (to release energy for the plant)
  4. Glucose is used to make other substances / converted into biomass (e.g. cellulose for cell walls, starch for storage, or proteins for growth)

Key terms in this question

endothermic · photosynthesis

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