A-LevelBiologyTransport in plants9700/42 · Oct/Nov 2025 · Q19 Marks

Rice, Oryza sativa, is a crop plant that has adapted to grow in flooded fields. Fig. 1.1 outlines the effects on rice plants of growing in flooded fields.

(a)With reference to Fig. 1.1, name: substance A substance B tissue C[3]
(b)Describe how root cells respond to a high concentration of substance B.[1]
(c)(i)Gibberellin is involved in the growth of stems in rice plants. Fig. 1.2 shows the effect of gibberellin concentration on the length of stems in rice plants. Describe the relationship shown in Fig. 1.2.[2]
(c)(ii)ABA in rice plant cells inhibits the action of gibberellin. With reference to Fig. 1.1 and Fig. 1.2, explain the importance of ethylene production for the growth of rice plants in flooded fields.[3]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2025). The mark or mark type is shown in brackets.

[3] (a) A oxygen; B ethanol; C aerenchyma ;
[1] (b) ref. to ethanol dehydrogenase (to break it down) ; A alcohol dehydrogenase
[2] (c)(i) as gibberellin concentration increases, the length of stem increases or positive correlation between concentration of gibberellin and length of stem ; data quote - two concentrations and two lengths with units ;
[3] (c)(ii) any three from : 1 ethylene causes break down of ABA, so gibberellin, active / stimulated / functional; 2 plants grow tall(er) / stems increase in length / stem elongation / increase in internodal length ; 3 (so) leaves / flowers, held above the water ; 4 (so) photosynthesis can occur / increased access to light / AW or (so) gas exchange / reproduction, can occur ;

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