Photosynthesis is the process by which plants produce glucose. Explain how the raw materials for photosynthesis are obtained by a plant and how they are used to produce glucose.

Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 3.1 Photosynthesis · Explain · 5 marks · View as Markdown

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

Plants are producers that carry out photosynthesis in order to make their own food. The overall word equation for photosynthesis is: carbon dioxide + water → glucose + oxygen.

Model answer (5 marks)

Carbon dioxide is taken in through the stomata on the leaf surface. Water is absorbed from the soil by the roots and moves up the stem by osmosis.
Light energy is captured by chlorophyll in the chloroplasts. The absorbed light energy drives the conversion of CO₂ and H₂O into glucose and O₂. The glucose produced can be used immediately for respiration, stored as starch, or incorporated into other molecules such as cellulose or proteins.

Examiner tips

  • Mention stomata for CO₂, roots for water, chlorophyll for light, and the conversion to glucose and O₂. Include a brief note on glucose utilisation. Keep the answer concise and use the exact terms.
  • Use the word ‘absorbed’ for CO₂ and water, and ‘captured’ for light energy to match the mark scheme.

Mark scheme (5 marks)

  1. Carbon dioxide is absorbed / taken in through the stomata (in the leaves)
  2. Water is absorbed from the soil by the roots (by osmosis)
  3. Light energy is absorbed / captured by chlorophyll (in the chloroplasts)
  4. Carbon dioxide and water are converted into glucose (and oxygen) using light energy
  5. Glucose can be used for respiration / stored as starch / used to make other biological molecules (e.g. cellulose, proteins)

Key terms in this question

photosynthesis · glucose

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