Page 97 - Biology Form Two

Biology for Secondary Schools

light intensity also increases the (vi) Atmospheric pressure: At high
plant’s internal temperature altitudes, the atmospheric pressure
and hence increases the rate of is low. This allows more rapid
transpiration. Light also increases diffusion of water. Plants at high
the rate of water absorption and altitudes experience a high rate of
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leads to an increased turgidity of
the two guard cells. The turgidity transpiration because of the low
of the guard cells brings about atmospheric pressure.
the opening of the stomata, hence
increasing the transpiration rate.

Activity 4.5: Determine the effect of environmental conditions on transpiration rate

Materials
Plant, potometer, beaker, trough, clock, and fan

Procedure
1. Cut off the shoot of the plant while immersed in water to prevent air bubbles
from entering the xylem of the stem.

2. Place the cutting in the potometer as shown in Figure 4.19. Allow the shoot
to transpire for a few minutes, while the end of the capillary tube is out of
water to introduce an air bubble in the tube. Then, immerse the end of the
capillary tube in water.

Shoot cutting
Capillary tube Reservoir

Beaker
Air bubble Scale

Water

Figure 4.19: Experimental set-up to investigate the rate of transpiration

Student’s Book - Form Two 91

05/10/2024 15:36:35
BIOLOGY FORM 2 NEW.indd 91
BIOLOGY FORM 2 NEW.indd 91 05/10/2024 15:36:35