A-LevelBiologyPhotosynthesis9700/42 · Feb/Mar 2023 · Q811 Marks

Describe the functions of the internal membranes of the chloroplast in photosynthesis.

(a)Describe the functions of the internal membranes of the chloroplast in photosynthesis.[7]
(b)Rubisco activase (RA) is an enzyme that has an effect on the activity of rubisco. An investigation was carried out on the effect of RA on the activity of rubisco. • Solutions of rubisco and RuBP were added to two tubes, A and B. • RA was added to tube A. • Both tubes were incubated at 25°C for 6 minutes. • The activity of rubisco was measured every 30 seconds. All conditions were kept the same, except for the addition of RA to tube A. The results are shown in Fig. 8.1. [Figure 8.1] Describe the results shown in Fig. 8.1 and suggest an explanation for the effect of RA on the activity of rubisco.[4]

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Mark scheme

Marking points from the official mark scheme (Feb/Mar 2023). The mark or mark type is shown in brackets.

[7] (a) any seven from:
[7] (a) 1 photosynthetic / named / primary / accessory, pigments to absorb light (energy);
[7] (a) 2 ref. to, photosystems / antenna complex and reaction centre / light harvesting structures ;
[7] (a) 3 photoactivation / electrons excited / emission of electrons ;
[7] (a) 4 electrons move along electron transport chain ;
[7] (a) 5 (cyclic/non-cyclic) photophosphorylation / light-dependent stage;
[7] (a) 6 site of photolysis / location of oxygen-evolving complex ;
[7] (a) 7 thylakoids stacked to form grana ;
[7] (a) 8 gives large surface area ;
[7] (a) 9 thylakoid space or lumen to, form proton gradient / have high concentration of protons ;
[7] (a) 10 thylakoid membrane is (relatively) impermeable, to maintain the proton gradient ;
[7] (a) 11 ATP synthase to make ATP;
[7] (a) 12 chemiosmosis ;
[4] (b) any four from:
[4] (b) describe
[4] (b) 1 A activity increases and B activity remains, low / constant ;
[4] (b) 2 comparative data quote ; e.g. 3.0-3.2 at 0.5 mins and 11.4–11.6 at 6 mins for A 0.4 throughout for B
[4] (b) max three: explanation:
[4] (b) 3 RA/rubisco activase, activates rubisco ;
[4] (b) 4 by changing the active site of rubisco;
[4] (b) 5 by enabling rubisco to bind more readily with, RuBP / substrate or more enzyme-substrate complexes;
[4] (b) 6 enables products to leave active site more quickly ;
[4] (b) 7 AVP; e.g. cofactor action qualified

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