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CAIE IGCSE Biology 8.3 Transpiration Questions

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

Syllabus
2026–2028
Course
Biology 0610

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 water8.3.2—Water evaporates from the surfaces8.3.3—Effects of variation of temperature8.3.4—Water vapour loss is related8.3.5—Mechanism by which water moves upwards8.3.6—Effects on the rate of transpiration8.3.7—Why wilting occurs

Question 1

[Maximum number: 16]

Question (a)

(a)

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

Fig. 3.1

Fig. 3.1

[ 4 ]

Question (i)

(i)

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

[ 1 ]

Question (ii)

(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 ]

Question (iii)

(iii)

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

[ 1 ]

Question (iv)

(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 ]

Question (b)

(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

Fig. 3.2

[ 8 ]

Question (i)

(i)

Using the information in Fig. 3.2, calculate how much water would be lost from 1 m21 \mathrm{~m}^{2} of leaves in 12 hours if the plants were kept at 35∘C35^{\circ} \mathrm{C}. Include the unit.

[ 3 ]

Question (ii)

(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 ]

Question (c)

(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 ]

Question (i)

(i)

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

[ 2 ]

Question (ii)

(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 ]

Question (iii)

(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 ]

Question 2

[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

Fig. 5.1

Question (a)

(a)

Describe the results shown in Fig. 5.1.

[ 3 ]

Question (b)

(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 ]

Question (c)

(c)

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

[ 1 ]
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