CAIE IGCSE Biology 8.3.6 Factors Affecting Transpiration Rate

Practise predicting and explaining how temperature, wind speed and humidity alter the rate of transpiration.

Exam points

predict a higher rate at warmer temperatures because evaporation and particle movement increase
predict a higher rate in wind because moving air removes humid air near the leaf
predict a lower rate at high humidity because the water-vapour concentration gradient is reduced

[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.

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8.3.6—Effects on the rate of transpiration question 1