1. 1
   A student grinds spinach leaves with propanone to extract the pigments and separates them by thin-layer chromatography. When the solvent front has moved 8.0 cm from the origin, four spots are visible: a yellow-orange spot 7.6 cm from the origin, a yellow spot 5.8 cm from the origin, a blue-green spot 4.4 cm from the origin and a yellow-green spot 3.2 cm from the origin.

   (a)

   What is the Rf value of the blue-green spot?

   [1 mark]

   • A0.55
   • B1.8
   • C0.45
   • D4.4

   (b)

   Which pigment is most likely to form the yellow-orange spot with the highest Rf value?

   [1 mark]

   • AChlorophyll a
   • BChlorophyll b
   • CXanthophyll
   • DCarotene

   (c)

   Explain why the pigments separate into different spots.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In an experiment on the unicellular alga Chlorella, two suspensions were given water and carbon dioxide containing different proportions of the heavy oxygen isotope ¹⁸O. Suspension 1 was given water with 0.85% ¹⁸O and carbon dioxide with the natural 0.20% ¹⁸O. Suspension 2 was given water with the natural 0.20% ¹⁸O and carbon dioxide with 0.61% ¹⁸O. In the light, the oxygen gas released by suspension 1 contained 0.85% ¹⁸O and the oxygen gas released by suspension 2 contained 0.20% ¹⁸O.

   (a)

   Which is the simple word equation for photosynthesis?

   [1 mark]

   • Aglucose + oxygen → carbon dioxide + water
   • Bcarbon dioxide + water → glucose + oxygen
   • Ccarbon dioxide + oxygen → glucose + water
   • Dwater + oxygen → glucose + carbon dioxide

   (b)

   Which conclusion is supported by these results?

   [1 mark]

   • AThe oxygen released comes from carbon dioxide
   • BThe oxygen released comes partly from water and partly from carbon dioxide
   • CThe oxygen released comes from water
   • DChlorella does not release oxygen in the light

   (c)

   Outline the role of the splitting of water in photosynthesis.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Equal lengths of the pondweed Elodea were placed in sodium hydrogencarbonate solution at 25 °C and lit through coloured filters that gave the same light intensity at each wavelength. The volume of oxygen collected in 10 minutes was: 430 nm (violet-blue) 3.6 cm³; 470 nm (blue) 3.0 cm³; 550 nm (green) 0.6 cm³; 600 nm (orange) 1.4 cm³; 670 nm (red) 3.2 cm³; 720 nm (far red) 0.3 cm³. Separately, a solution of the chlorophylls extracted from the same pondweed absorbed these percentages of the light at each wavelength: 430 nm 88%; 470 nm 55%; 550 nm 4%; 600 nm 18%; 670 nm 82%; 720 nm 3%.

   (a)

   Determine the rate of oxygen production at 670 nm in cm³ h⁻¹ and compare it with the rate in green light, suggesting a reason for the difference.

   [3 marks]

   (b)

   Evaluate the hypothesis that the rate of photosynthesis at each wavelength depends only on the light absorbed by chlorophyll.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   In a free-air carbon dioxide enrichment (FACE) experiment, circular plots of wheat growing in a farm field were surrounded by rings of pipes that released carbon dioxide into the wind, raising the concentration around the plants from 415 ppm to 550 ppm. Control rings had pipes but released no extra carbon dioxide. The rate of photosynthesis of leaves in enriched plots was 31% higher than in control plots, and grain yield was 12% higher. On plots given little nitrogen fertiliser, grain yield rose by only 5%. Earlier experiments in enclosed greenhouses using the same enrichment had reported yield increases of 25–30%.

   (a)

   Describe how an experiment could be carried out in the laboratory to test a hypothesis about the effect of carbon dioxide concentration on the rate of photosynthesis.

   [6 marks]

   (b)

   Discuss the use of FACE and greenhouse experiments to predict how rates of photosynthesis and crop growth will change as atmospheric carbon dioxide rises.

   [6 marks]

   Total for question 4: 12 marks

End of questions