A researcher places moss in a transparent chamber and measures its rate of carbon dioxide uptake. Light intensity and carbon dioxide concentration are kept constant. The rate decreases when the chamber is cooled from 22 ∘C22\ ^\circ\text{C}22 ∘C to 8 ∘C8\ ^\circ\text{C}8 ∘C. When the chamber is returned to 22 ∘C22\ ^\circ\text{C}22 ∘C, the original rate is restored.
Which statement explains this?
Cooling slows the enzyme-controlled reactions without denaturing the enzymes, so warming restores the rate.
Cooling makes carbon dioxide the limiting factor, but warming makes light the limiting factor instead.
Cooling denatures the enzymes, but warming allows their active sites to regain their original shape.
Cooling stops respiration, so the moss has less carbon dioxide available until it is warmed.
117 exam-style questions on OCR GCSE Biology 1.4 Photosynthesis, covering 1.4.1 Photosynthesisers as biomass producers, 1.4.2 Factors affecting the rate of photosynthesis, and 1.4.3 Limiting factors in photosynthesis. Each one has a worked solution and a mark scheme showing where the marks go.