Biology · May / June 2024 · Paper 41 · Question 5
0610
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Fig. 5.1 is a graph showing the effect of temperature on the rate of transpiration from the upper and lower surfaces of a leaf that is provided with a constant supply of water. X Y lower surface upper surface temperature rate of transpiration Fig. 5.1
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5(a)[3]
any three from:
rate of transpiration increases and then remains constant with increasing temperature ; ora
(the rate of transpiration) is higher from the lower surface ;
rates of both become constant at (nearly) the same temperature ;
transpiration from lower surface increases, at a greater rate / faster, than from the upper surface (in X) ;
5(b)[4]
total of four from:
X to max 3:
as temperature increases and rate increases
1
the rate of evaporation from the mesophyll (cells) increases ;
2
the rate of diffusion of water vapour (through the stomata / from the leaf) increases ;
3
particles / molecules, have more kinetic energy / move faster ;
4
temperature is the limiting factor (for transpiration) ;
5
more stomata opening / stomata open wider ;
Y to max 3:
as temperature increases and rate remains constant
6
rate of diffusion of water vapour through stomata at a maximum ; 7
evaporation from mesophyll (cells) at a maximum ;
8
rate of movement of water in xylem slows ;
9
rate of uptake of water is at a maximum ;
10 the stomata are, all / fully, open ;
11 humidity / light intensity / number of stomata, is the limiting factor ;
5(c)[1]
more stomata on the lower surface / lower surface has a thinner cuticle ;
ora
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