Page 98 - Biology Form Two

Biology for Secondary Schools

3. Leave the apparatus for two hours (v) It helps to balance water
in bright sunlight. levels within the plant through
continuous elimination of water
4. Observe the position of the water

bubble. The distance the bubble from the plant body.
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travels shows how much water (vi) It maintains osmosis and keeps
the stem has taken up. the cells rigid.

5. Repeat the experiment under Guttation

different conditions; for example, Guttation is the oozing out of drops
use a fan to create air movement of water on the tips or edges of leaves
or apply some petroleum jelly on of some vascular plants through small
some of the leaves to reduce the pores or openings called hydathodes.

number of stomata. Guttation occurs at night when the
rate of transpiration is low because
6. Record your results and compare the stomata are closed. In addition,
them with those obtained in Step 4 at night the soil is relatively moist,
using a tabular form. The distance hence water will enter the plant roots.
moved by an air bubble can be Guttation can also occur when there

recorded every minute and used to is too much water in the soil. In this
indicate the rate of water uptake case, water potential in the roots is
by the plant.
lower than that of the surrounding soil.

Significance of transpiration As a result, water will enter the root
hairs and become accumulated in the
(i) It helps to maintain transpiration
pull which is important for xylem and set the root pressure. This
maintaining a constant stream of pressure forces some water to exit the
water and minerals between the leaf tip or edge through the structures
roots and the leaves. called hydathodes or water glands, and
(ii) It enables the loss of excess water form drops. Figure 4.20 show a leaf
from the plant. undergone gutation

(iii) It helps to cool the plant.

(iv) It enables the absorption and
conduction of water and mineral

salts to different parts of the plant.

92 Student’s Book - Form Two

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BIOLOGY FORM 2 NEW.indd 92