Explain why a plant kept in complete darkness for several days will eventually stop growing and may die.

OCR GCSE Biology A: Gateway Science (J247) — B1.4 Photosynthesis · Explain · 4 marks · View as Markdown

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

A houseplant is moved into a completely dark cupboard for several days. After this time, the plant appears wilted, its leaves have turned yellow, and new growth has stopped.

Model answer (4 marks)

In darkness there is no light energy for photosynthesis to occur.

Photosynthesis converts CO₂ and H₂O into glucose (and O₂).

Without photosynthesis no glucose is produced, so the plant has no energy source for cellular respiration.

Glucose is also required as a building block for other molecules such as cellulose, proteins and lipids that are needed for growth.

Examiner tips

  • Use the exact terms ‘photosynthesis’, ‘glucose’, ‘cellular respiration’, ‘cellulose’, ‘proteins’, ‘lipids’.
  • Show the causal chain: darkness → no photosynthesis → no glucose → no energy & building blocks → no growth.
  • Keep the answer concise, 4 points, one sentence per point.

Common mistakes

  • Confusing photosynthesis with respiration, or saying the plant still has energy from stored starch.
  • Mentioning chlorophyll breakdown or light‑dependent reactions instead of the key point that no light means no photosynthesis.

Mark scheme (4 marks)

  1. In darkness there is no light energy available for photosynthesis to occur
  2. Photosynthesis converts carbon dioxide and water into glucose (and oxygen)
  3. Without photosynthesis, no glucose is produced, so the plant has no source of energy / no substrate for cellular respiration
  4. Glucose is also needed as a building block / raw material to make other biological molecules (e.g. cellulose / proteins / lipids) required for growth

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