A-LevelBiologyCell membranes and transport9700/42 · Feb/Mar 2021 · Q510 Marks

Many processes and actions in plants and animals are due to the movement of ions. Table 5.1 lists several ions, the direction of movement of each ion and the action resulting from that movement.

(a)Complete Table 5.1. [Table 5.1][6]
(b)(i)Name the ion that moves into the cells at the base of the sensory hairs to generate receptor potentials.[1]
(b)(ii)If two or more of these hairs are stimulated within a period of 20–35 seconds, action potentials are generated, causing the leaf to close quickly and trap the insect. Suggest why it is beneficial to the plant for stimulation of two or more hairs to be necessary before the leaf will close.[1]
(b)(iii)The trapped insect is digested by enzymes released from the leaf cells. Name the mechanism by which the enzymes are released.[1]
(b)(iv)Suggest why Venus fly trap plants need to capture insects.[1]

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Mark scheme

Marking points from the official mark scheme (Feb/Mar 2021). The mark or mark type is shown in brackets.

[1] co-transport/secondary active transport, of, amino acids / glucose or osmosis of water ;
[1] K+;
[1] opening of stoma(ta)
[1] Na+;
[1] depolarisation of presynaptic membrane
[1] Ca2+;
[1] exocytosis of acetylcholine
[1] H+;
[1] ATP synthesis ;
[1] Ca2+;
[1] binds to troponin / troponin shape changes / tropomyosin moves / actin binding site on myosin head exposed / binding of myosin head to actin / allows power stroke / sarcomere contracts;
[1] Ca2+ / calcium ions ;
[1] to avoid wasting energy or idea of avoid closing, due to a single contact / by an object such as water drop;
[1] exocytosis;
[1] not enough, nitrogen / nitrate, in the soil or poor mineral content of the soil ; R nutrients

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