O-LevelBiologyCoordination & Response5090/22 · May/June 2016 · Q411 Marks

Fig. 4.1 shows the leaves of the same plant during daylight and during the hours of darkness. [Figure 4.1(a) in daylight; Figure 4.1(b) in darkness]

(a)Name a process that takes place in the plant in Fig. 4.1(a) only during daylight and explain how the leaves help this process. process explanation[3]
(b)The folding of the leaves at night, as seen in Fig. 4.1(b), is called a sleep movement. Suggest and explain the effect of these sleep movements on the loss of water from one of these plants. effect explanation[4]
(c)Fig. 4.2 shows the uptake and loss of oxygen by a leaf during a 24-hour period. [Figure 4.2]
(c)(i)Explain what is happening in the leaf at the following times: between 1800 hours and 2000 hours[2]
(c)(ii)after 2200 hours.[2]

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Mark scheme

Marking points from the official mark scheme (May/June 2016). The mark or mark type is shown in brackets.

[1] process: photosynthesis ;
[max 2] explanation: 1. leaves flat ;
2. face the sun/horizontal ;
3. large/maximum/increased + surface area ;
4. (for) trapping/absorbing /converting + light (energy);
5. (for) CO2 absorption/reference to stomata;
6. presence of chlorophyll /chloroplasts;
7. reference to transparent cuticle /epidermis/thin leaves ;
8. reference to intercellular spaces/mesophyll cells ;
9. reference to veins to bring water/take away products;
[1] effect: reduces (transpiration); Ig wilting
[max 3] explanation: stomata;
(mostly) on lower surface ;
any two of: humidity build up/reduced diffusion gradient/reduced evaporation (rate)/reduced surface area/(stomata/guard cells) close ;;
protection from breeze/wind ;
[max 2] reduced light levels;
photosynthesis slowing down ;
less O2 produced/lost AW ;
stomata closing/closed AW ;
[max 2] reference to darkness/low light intensity;
photosynthesis stops;
O2 used/absorbed/gained/uptake AW;
(for) respiration ;

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