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Photosynthesis

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Question 10

A scientist investigated the photosynthetic rate of a marine cyanobacterium under controlled conditions and noted the following observations:

  • Under white light, the cyanobacterium appears blue-green.
  • At 15∘C15^\circ\text{C}15∘C, the rate of carbon dioxide uptake increases linearly as light intensity increases up to 200 μmol m−2 s−1200\ \mu\text{mol}\ \text{m}^{-2}\ \text{s}^{-1}200 μmol m−2 s−1.
  • Above 200 μmol m−2 s−1200\ \mu\text{mol}\ \text{m}^{-2}\ \text{s}^{-1}200 μmol m−2 s−1, the rate of carbon dioxide uptake remains constant, but it increases significantly if the temperature is raised to 25∘C25^\circ\text{C}25∘C.

Which of the following statements, A to D, correctly explains these observations?

A

The pigments absorb red and orange light, and at light intensities above 200 μmol m−2 s−1200\ \mu\text{mol}\ \text{m}^{-2}\ \text{s}^{-1}200 μmol m−2 s−1, temperature is a limiting factor.

B

The pigments absorb blue and green light, and at light intensities above 200 μmol m−2 s−1200\ \mu\text{mol}\ \text{m}^{-2}\ \text{s}^{-1}200 μmol m−2 s−1, temperature is a limiting factor.

C

The pigments absorb red and orange light, and at light intensities below 200 μmol m−2 s−1200\ \mu\text{mol}\ \text{m}^{-2}\ \text{s}^{-1}200 μmol m−2 s−1, temperature is a limiting factor.

D

The pigments absorb blue and green light, and at light intensities below 200 μmol m−2 s−1200\ \mu\text{mol}\ \text{m}^{-2}\ \text{s}^{-1}200 μmol m−2 s−1, light intensity is not a limiting factor.

Markscheme

Photosynthesis Questions

  1. A Level
  2. /Biology
  3. /Photosynthesis

16 exam-style questions on OCR A A Level Biology Photosynthesis. Each one has a worked solution and a mark scheme showing where the marks go.

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