Page 93 - Biology Form Two

Biology for Secondary Schools

have a narrow lumen which makes it whereby adhesion occurs between
possible for water to rise in them by water molecules and the surface of the
capillarity. Capillarity is made possible xylem. Adhesive force causes water
by cohesive and adhesive forces. The molecules to adhere to the xylem
cohesive force is a force of attraction vessels. Capillarity occurs when the
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between molecules of the same type as adhesion of water molecules to the
opposed to the adhesive force which walls of the vessel is stronger than
involves attraction between different the cohesive forces between the water
molecules. Cohesive force makes the molecules.
water molecules stick to each other

Activity 4.3: Demonstrate capillarity

Materials
Glass tubes of different diameters, beaker, coloured water, and retort stand

Safety precaution
Handle glass materials with care to prevent breakage.

Procedure
1. Pour coloured water into the beaker.
2. Put glass tubes of different diameters into the water but not touching the
bottom of the beaker. Clamp the tubes to hold them in place (Figure 5.15).

Capilary tube

Retort stand
Beaker

Coloured water

Figure 4.15: Experimental set-up to demonstrate capillarity

3. Observe how water rises in the glass tubes.
4. Compare the levels of water in the tubes. What have you observed?
5. Write a short report of what you have observed.

Student’s Book - Form Two 87

05/10/2024 15:36:34
BIOLOGY FORM 2 NEW.indd 87
BIOLOGY FORM 2 NEW.indd 87 05/10/2024 15:36:34