Photosynthesis is an energy transfer process that results in the production of carbohydrate. It has two stages: the light-dependent stage and the light-independent stage. Cyclic photophosphorylation and non-cyclic photophosphorylation are essential pathways in photosynthesis that occur in the light-dependent stage.

1. (a)(i)Describe the similarities and differences between cyclic photophosphorylation and non-cyclic photophosphorylation.[4]
2. (a)(ii)Explain why herbicides that prevent cyclic photophosphorylation and non-cyclic photophosphorylation stop carbohydrate being produced in the chloroplast.[2]
3. (b)(i)The rate of regeneration of RuBP in the Calvin cycle is known to limit the rate of photosynthesis. Sedoheptulose-1,7-bisphosphatase (SBPase) is an enzyme in the Calvin cycle that controls the rate of regeneration of RuBP. SBPase is coded for by the gene SBPase. In an experiment, wheat plants were genetically modified to make more SBPase by introducing the SBPase gene from another grass species, Brachypodium distachyon. The resulting GM wheat plants were named Sox4. • Wild type plants (not GM) and Sox4 plants were grown. • A leaf from the wild type plant was placed in a sealed glass vessel. • The carbon dioxide (CO2) concentration in the vessel was increased so that the intercellular air spaces also had an increase in CO2 concentration. • The other environmental conditions were kept constant. • The rate of fixation of CO2 was measured for the leaf. • The experiment was repeated with a leaf from a Sox4 plant. [Figure 2.1] shows the rate of fixation of CO2 by the leaves of wild type plants and Sox4 plants when the intercellular air space CO2 concentration was increased.[4]
4. (b)(ii)With reference to [Figure 2.1], describe and suggest explanations for the differences in the rate of fixation of CO2 between wild type plants and Sox4 plants.[3]

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