CAIE IGCSE Biology 8.3 Transpiration Question Bank

Practise transpiration questions on water vapour loss from leaves, stomatal diffusion, environmental-rate graphs, xylem pull and wilting under water stress.

Exam points

define transpiration as water vapour loss from leaves through evaporation and stomatal diffusion
interpret rate graphs for temperature, wind or humidity using diffusion gradients
explain wilting or transpiration pull using turgor loss, cohesion and xylem water supply

Covered syllabus points

8.3.1—Transpiration as the loss of water 8.3.2—Water evaporates from the surfaces 8.3.3—Effects of variation of temperature 8.3.4—Water vapour loss is related 8.3.5—Mechanism by which water moves upwards 8.3.6—Effects on the rate of transpiration 8.3.7—Why wilting occurs

[Maximum number: 16]

(a)

Fig. 3.1 shows some apparatus that was used to investigate water loss from a leafy shoot.

Fig. 3.1

[ 4 ]

(i)

State the name of the process by which leafy shoots lose water.

[ 1 ]

(ii)

Before the leafy shoot is inserted into the jar shown in Fig. 3.1, it must be recut under water.

Suggest why the end of the leafy shoot was cut under water.

[ 1 ]

(iii)

State the purpose of the oil layer on top of the water in the burette.

[ 1 ]

(iv)

Using the information in Fig. 3.1, describe one method that can be used to determine how much water is lost from the leafy shoot.

[ 1 ]

(b)

The apparatus shown in Fig. 3.1 was used to investigate the effect of temperature on the rate of water loss in a species of plant. The results are shown in Fig. 3.2.

Fig. 3.2

[ 8 ]

(i)

Using the information in Fig. 3.2, calculate how much water would be lost from $1 \mathrm{~m}^{2}$ of leaves in 12 hours if the plants were kept at $35^{\circ} \mathrm{C}$ . Include the unit.

[ 3 ]

$12096 \mathrm{~g}\left(\right.$ per $\left.\mathrm{m}^{2}\right) / 12.096 \mathrm{~kg}\left(\right.$ per $\left.\mathrm{m}^{2}\right)$ ;;;

A $12 / 12.1 \mathrm{~kg}\left(\right.$ per $\left.\mathrm{m}^{2}\right)$

MP1 correct reading from graph 0.28 (g per $\mathrm{m}^{2}$ per s) MP2 correct calculation $0.28 \times 60 \times 60 \times 12=12096 \mathrm{~g}$ MP3 correct unit - g or kg ;

Marking guidance:

ecf for MP2 from incorrect MP1

(ii)

Using the information in Fig. 3.2, describe and explain the effect of increasing temperature on the rate of water loss in this species of plant.

[ 5 ]

any five from:

1 as temperature increases, (rate of) water loss increases ;

2 ref to steeper rate / greater loss of water, after $37 / 38^{\circ} \mathrm{C}$ ;

3 any correct comparative data quote (with units at least once) ;

4 water vapour lost, through stomata / between guard cells ;

5 evaporation from mesophyll into air spaces ;

6 (diffusion) down a, water potential, gradient ;

7 increasing temperature increases kinetic energy (of water molecule) ;

8 faster (rate of) more, diffusion ;

9 stomata open wider / more stomata open in high(er) temperatures ;

10 AVP ;

e.g. transpiration / evaporation, cools the plant

(c)

The apparatus shown in Fig. 3.1 can also be used to investigate the effects of changing humidity on water loss in plants.

[ 4 ]

(i)

Suggest why the mass of water in the apparatus does not change when the leafy shoot is kept at 100 % relative humidity.

[ 2 ]

(ii)

Even at extremely low relative humidities the leafy shoot did not wilt.

Explain why the leafy shoot shown in Fig. 3.1 did not wilt.

[ 1 ]

(iii)

The investigation on the effect of temperature was done at a relative humidity of 20 %.

The investigation was repeated at a relative humidity of 80 % and all other conditions were kept the same.

Predict how the water loss will differ from the trend shown in Fig. 3.2.
Sketch your prediction on Fig. 3.2.

[ 1 ]

[Maximum number: 6]

(a)

Some students set up the apparatus shown in Fig. 6.1 to compare transpiration in two sets of leaves.

Set A was kept in a transparent bag and set B was left in the open air.
All other conditions were kept constant.
The mass of the leaves in each set was measured at the start of the investigation and after five hours.

Fig. 6.1

[ 6 ]

(i)

Predict the results for this investigation.

Explain the reason for your prediction. prediction
explanation

[ 3 ]

(ii)

Explain how transpiration occurred in the leaves shown in Fig. 6.1.

[ 3 ]

[Maximum number: 8]

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.

Fig. 5.1

(a)

Describe the results shown in Fig. 5.1.

[ 3 ]

(b)

Explain reasons for the shape of the graph for the upper surface of the leaf at X and at Y in Fig. 5.1.
at X
at Y

[ 4 ]

(c)

Suggest how the structure of the lower surface differs from the upper surface of the leaf used in this investigation.

[ 1 ]

All question bank results loaded

Covered syllabus points

8.3 Transpiration question 1

Question (a)

Question (i)

Question (ii)

Question (iii)

Question (iv)

Question (b)

Question (i)

Question (ii)

Question (c)

Question (i)

Question (ii)

Question (iii)

8.3 Transpiration question 2

Question (a)

Question (i)

Question (ii)

8.3 Transpiration question 3

Question (a)

Question (b)

Question (c)