A-LevelBiologyPhotosynthesis9700/42 · Oct/Nov 2023 · Q812 Marks

Non-cyclic photophosphorylation occurs in the light-dependent stage of photosynthesis. Outline the main features of non-cyclic photophosphorylation.

(a)Non-cyclic photophosphorylation occurs in the light-dependent stage of photosynthesis. Outline the main features of non-cyclic photophosphorylation.[4]
(b)Some Calvin cycle intermediates are used to produce other molecules that are not part of the Calvin cycle. Name two of these intermediates. For each intermediate, state one example of the type of molecule that is produced. intermediate molecule produced intermediate molecule produced[2]
(c)(i)Fig. 8.1 shows how the rate of uptake of carbon dioxide by a plant varies with temperature, at an optimum intensity of light on a clear day. [Figure 8.1] Calculate the mean increase in rate of uptake of carbon dioxide as the temperature increases from 5°C to 20 °C. Show your working. Give your answer to two decimal places.[2]
(c)(ii)Suggest why the rate of carbon dioxide uptake levels off and then decreases after 20°C.[3]
(c)(iii)On Fig. 8.1, draw a curve to show the uptake of carbon dioxide on a cloudy day.[1]

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Mark scheme

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

[1] (a) both photosystem I and photosystem II involved ; A both photosystems
[1] (a) photoactivation of chlorophyll occurs ;
[1] (a) photolysis of water occurs / description;
[1] (a) oxygen production / oxygen-evolving complex involved ;
[1] (a) electrons emitted by photosystem I used to reduce NADP or NADP is the final electron acceptor;
[1] (a) photosystem I receives electrons from photosystem II or photosystem II receives electrons from photolysis (of water) ;
[1] (a) ETC / electron transport chain, sets up proton gradient or chemiosmosis / ATP produced ;
[1] (b) GP used to make, amino acids / fatty acids / lipids ;
[1] (b) TP used to make, hexose / starch / cellulose / amino acids / glycerol / lipids ;
[1] (c)(i) 3.10 – 1.55 or 3.10 – 1.50 (correct values from graph)
[1] (c)(i) / 15 (correct division by temperature range) = 0.10/0.11 (correct final answer);
[1] (c)(ii) temperature now not limiting or carbon dioxide concentration now limiting;
[1] (c)(ii) closure of stomata;
[1] (c)(ii) lack of water / AW ;
[1] (c)(ii) denaturation of enzymes or active site no longer complementary to substrate / no ESCs form ;
[1] (c)(ii) AVP; e.g. ref. to optimum temperature / photorespiration occurs
[1] (c)(iii) similar shape but below high intensity curve ;

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