Transpiration is the loss of water vapour from the leaves of a plant. A student used a potometer to investigate the effect of wind speed on transpiration. Fig. 2.2 shows part of the apparatus used. The air bubble in the tubing will move towards the leafy shoot because water moves into the stem when water is lost from the leaves. Fig. 2.2 The student used this method: - Cut a leafy shoot from a plant. - $$$\quad$$$ Place the leafy shoot into the potometer. - Measure the distance the air bubble moves in five minutes at different wind speeds. - Maintain the temperature in the room at $$$25^{\circ} \mathrm{C}$$$ and the relative humidity at $$$60 \%$$$. - Repeat the investigation using five different leafy shoots. Each shoot must have the same number of leaves. Using your graph, estimate the distance the air bubble moved in five minutes when the wind speed was $$$15 \mathrm{~km}$$$ per hour. Show on your graph how you obtained your estimate. $$$\mathrm{mm}$$$

Biology

IGCSE&ALevel

CAIE

Exam No：0610_w23_qp_63 Year：2023 Question No：2(b)(vi)

Answer:

value from candidate's graph (mm); indications on graph as to where reading taken ;

Knowledge points:

8.1.1 State the functions of xylem and phloem

8.1.2 Identify the position of xylem and phloem as seen in sections of roots, stems and leaves, limited to non-woody dicotyledonous plants

8.3.1 State that water is transported from the roots to leaves through the xylem vessels

8.3.2 Define transpiration as loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by diffusion of water vapour through the stomata

8.3.3 Investigate and describe the effects of variation of temperature and humidity on transpiration rate

8.3.4 Explain how water vapour loss is related to the large surface area of cell surfaces, interconnecting air spaces and stomata

8.3.5 Explain the mechanism by which water moves upwards in the xylem in terms of a transpiration pull that draws up a column of water molecules, held together by cohesion

8.3.6 Explain how and why wilting occurs

8.3.7 Explain the effects of variation of temperature and humidity on transpiration rate

Answer:

Knowledge points:

Solution:

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