O-LevelBiologyTransport in Plants5090/21 · May/June 2017 · Q211 Marks

A potometer is used to measure water uptake by a plant. Fig. 2.1 shows the stem and flower of a plant in a potometer. As water is taken up, the bubble moves in the direction shown. [Figure 2.1]

(a)Name the parts A, B, C and D in Fig. 2.1. A B C D[4]
(b)Describe the pathway taken by water as it moves from the potometer, through the plant stem and into the surrounding air.[3]
(c)(i)In an experiment, the bubble moved a distance of 60mm in 10 minutes. Calculate the average rate at which the bubble moved in mm per min. mm per min[1]
(c)(ii)The experiment was repeated in an area of lower light intensity. Predict and explain what would happen to the rate at which the bubble moved. prediction....................................................................................................................................................................................................................................................................................... explanation.......................................................................................................................................................................................................................................................................................[3]

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Mark scheme

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

[4] 2(a) (A) petal; (B) sepal; (C) leaf/lamina / cuticle; (D) vein / midrib / vascular (tissue) OR xylem + phloem ;
[3] 2(b) xylem; to leaves / flower(s) ; between leaf cells; surface of mesophyll cells ; (leaf) air spaces ; (through) stomata / guard cells ;
[1] 2(c)(i) 6;
[3] 2(c)(ii) reduces / lower(s) AW ; less photosynthesis ; less water needed; stomata / guard cells + open less / are closed ; less diffusion ; less evaporation / transpiration ;

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