Explain why farmers growing crops in greenhouses sometimes pump extra carbon dioxide into the greenhouse and also use artificial lighting at night.

AQA A-Level Biology (7402) — 3.5.1 Photosynthesis · Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

Farmers add CO₂ because it is a reactant in photosynthesis; a higher CO₂ concentration increases the rate of photosynthesis, producing more glucose. They also use artificial lighting at night because light is an energy source for photosynthesis; the extra light extends the period during which the plant can photosynthesise, preventing light from being a limiting factor. The greater rate of photosynthesis results in more glucose, leading to faster and greater plant growth and higher yield.

Examiner tips

  • Mention CO₂ as a reactant and its effect on rate; state light as energy source and its role at night; link increased rate to more glucose and growth; keep answer concise and use correct terminology

Common mistakes

  • Forgetting that CO₂ is a reactant; confusing CO₂ with water; not linking increased photosynthesis to increased biomass

Mark scheme (5 marks)

  1. Carbon dioxide is a reactant in / raw material for photosynthesis
  2. Increasing carbon dioxide concentration increases the rate of photosynthesis (so more glucose is produced)
  3. Light is a reactant / energy source for photosynthesis
  4. Artificial lighting at night extends the period during which the plant can photosynthesise / prevents light from being a limiting factor at night
  5. Greater rate of photosynthesis means more glucose produced, leading to faster / greater plant growth (increased biomass / yield)

Key terms in this question

carbon dioxide

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