O-LevelBiologyTransport in Plants5090/22 · May/June 2017 · Q49 Marks

Table 4.1 shows the loss of water vapour by two similarly-sized potted plants, F and G, grown in the same environment over a period of 14 hours. Table 4.1 water vapour loss/arbitrary units time of day/hours | plant F | plant G ------------------|---------|--------- 06.00 – 08.00 | 1.0 | 5.2 08.00 – 10.00 | 2.0 | 13.8 10.00 – 12.00 | 5.8 | 14.8 12.00 – 14.00 | 4.8 | 9.2 14.00 – 16.00 | 3.6 | 6.8 16.00 – 18.00 | 3.0 | 4.4 18.00 – 20.00 | 2.0 | 1.0

(a)State the time of day at which the combined loss of water vapour from the two plants is at its greatest.[1]
(b)(i)the difference between the total amount of water vapour lost by plants F and G during the 14-hour period,[3]
(b)(ii)the change in rate of water vapour loss by plant F from 06.00 hours to 12.00 hours.[3]
(c)The leaves of plant G have their lowest temperature at 12.00 hours. Suggest reasons for this.[2]

Mark scheme

Marking points from the official mark scheme (May/June 2017). The mark or mark type is shown in brackets.

[1] (a) 10.00-12.00 / noon / midday;
[3] (b)(i) 1 plants may be of different species; 2 plant G + more / fast(er) transpiration ; 3 plant G + more / big(ger) leaves ; 4 plant G + more stomata / pores / guard cells OR stomata bigger / wider AW ; 5 plant G + better / big(ger) root system / absorbs more water ; 6 plant G + thin(ner) (waxy) cuticle ;
[3] (b)(ii) 1 increased + light (intensity); 2 increased + temperature / heat ; 3 reference to wind OR increased + air movement; 4 decreased + humidity; 5 stomata / pores / guard cells + open /wider ;
[2] (c) 1 highest / fastest (rate of) / most ; 2 (evapo) transpiration / evaporation ; 3 reference to previous 4 hours / between 8:00–12:00 / from 8:00 ; 4 (evaporation) cools (plant / leaves) / removes heat / temperature falls;

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