A-LevelBiologyControl and coordination9700/42 · Oct/Nov 2019 · Q712 Marks

The Venus fly trap, Dionaea muscipula, is a carnivorous plant, native to wetlands of the East Coast of the USA. Mineral ions from decayed organisms are often washed away in these wetlands. Fig. 7.1 shows a Venus fly trap leaf.

(a)Suggest why a Venus fly trap benefits from catching insects in these wetlands.[2]
(b)(i)The leaves of the Venus fly trap will close if stimulated by an insect. State which part of the leaf detects the stimulus.[1]
(b)(ii)Explain how the plant does not waste energy by closing when it does not need to, such as when a large drop of rain touches the receptor.[1]
(c)With reference to Fig. 7.2 and Fig. 7.3, describe how the action potential of the Venus fly trap differs from that of a human.[3]
(d)Describe how the production of action potentials in the leaf cells of the Venus fly trap can result in the leaves closing and trapping an insect.[5]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2019). The mark or mark type is shown in brackets.

[1] low, mineral (ions) / named mineral (ion), content of soil
[1] insects provide, mineral (ion) / named mineral (ion) / amino acids, for growth
[1] (sensory / trigger / receptor) hair
[1] at least two hairs must be touched within, 35 seconds / short time period / at same time or one hair touched twice, within, 35 seconds / short time period
[1] smaller change in membrane potential / smaller depolarisation
[1] longer duration of action potential / shorter duration of depolarisation
[1] shorter duration of repolarisation / longer duration of hyperpolarisation
[1] longer refractory period
[1] data quote to support either mp1, mp2, mp3 or mp4
[1] membrane / resting, potential 0mV compared with -70mV for human
[1] action potential / depolarisation, reaches lobe (of leaf)
[1] ref. to hinge / midrib, cells
[1] H+, pumped out of cells / pumped into cell walls
[1] cell wall, loosens / cross-links broken
[1] calcium pectate, dissolves / breaks down (in middle lamella)
[1] Ca2+ (ions) enter cells
[1] water enters, by osmosis / down water potential gradient
[1] (hinge / midrib) cells, expand / become turgid
[1] leaves / lobes, become concave

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