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.

Exam points

Define transpiration as water vapour loss from leaves and distinguish it from liquid water movement through roots and xylem.
Explain evaporation from moist mesophyll surfaces and diffusion of water vapour through leaf air spaces and open stomata down a concentration gradient.
Interpret rate graphs or investigation data for temperature, wind and humidity, using controlled variables and water-vapour gradients to justify trends.
Explain transpiration pull using cohesion and a continuous column of water in xylem.
Predict wilting when water loss exceeds uptake, linking water stress to falling turgor and flaccid cells.

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: 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 ]

[Maximum number: 15]

(a)

A student investigated the effect of temperature on transpiration.

The student collected four small plants and placed them in beakers filled with water.
Fig. 3.1 shows the apparatus used.

Fig. 3.1

For each plant, the student measured the initial masses of the equipment, water and plant.
Each plant was placed in a different temperature-controlled room for three hours.
After three hours, the student measured the final masses of the equipment, water and plants.

The results are shown in Table 3.1.

Table 3.1

[ 12 ]

(i)

Describe and explain the difference in the results for the plants kept at $15^{\circ} \mathrm{C}$ and $25^{\circ} \mathrm{C}$ .

[ 4 ]

(ii)

The investigation was repeated with a plant kept at $25^{\circ} \mathrm{C}$ in a lower humidity environment.

Predict the effect of these conditions on the transpiration rate.
Explain your prediction.

[ 2 ]

(iii)

Complete the sentences about water movement through the xylem.

The xylem transports water and ______.

Xylem cells form a long continuous ______ with thick walls containing cellulose and ______.

Water moves upwards in the xylem because of transpiration ______.

This draws up a ______ of water molecules, held together by ______ between water molecules.

[ 6 ]

(b)

Explain why wilting occurs.

[ 3 ]

[Maximum number: 1]

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

Fig. 3.1

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

[Maximum number: 3]

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

Describe the results shown in Fig. 5.1.

[Maximum number: 1]

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

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

[Maximum number: 6]

A student investigated the effect of temperature on transpiration.

The student collected four small plants and placed them in beakers filled with water.
Fig. 3.1 shows the apparatus used.

Fig. 3.1

Table 3.1

[Maximum number: 3]

Scientists investigated the effect of cuticle thickness on water loss from the leaves of the balsam fir tree, Abies balsamea.

The leaves were divided into three groups:

A - thick cuticle

B - medium cuticle

C - thin cuticle

Samples of leaves from each group were weighed. The leaves were placed on a tray in dry air at $20^{\circ} \mathrm{C}$ . The samples of leaves were reweighed, at intervals, over 15 hours. The scientists calculated the mass of each sample of leaves as a percentage of the initial mass.

mass of the leaves as a percentage of the initial mass

Fig. 5.1 shows the results.

The investigation was repeated on a day when the air humidity was higher.

Suggest and explain the effect that this would have on the results.

[Maximum number: 3]

Explain why wilting occurs.

All question bank results loaded

Covered syllabus points

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)

Question 2

Question (a)

Question (b)

Question (c)

Question 3

Question (a)

Question (i)

Question (ii)

Question (iii)

Question (b)

Question 4

Question 5

Question 6

Question 7

Question 8

Question 9