Page 72 - Biology Form Two

Biology for Secondary Schools

4. Leave the mixture completely the other solution. This solution is
undisturbed overnight. hypotonic, meaning that it has a lower
solute potential or higher water potential.
5. Describe the colour distribution.
The second solution should have a lesser
6. Repeat the activity using copper volume of water and a greater quantity
FOR ONLINE READING ONLY
sulphate or laundry blue instead of solute than the other solution. This

of potassium permanganate or tea solution is hypertonic, meaning that it
bags. has a higher solute potential or lower
water potential. If the two solutions have
7. Explain your observations.
the same water or solute potential, then,
Questions they are said to be isotonic.
1. How did the colour of potassium Sucrose molecule
permanganate spread in the water Partially permeable Water molecule
membrane
in the test tube?

2. How long did it take for the colour
to spread evenly in the test tube?

Osmosis
Osmosis is a passive diffusion of water Hypotonic solution Hypertonic solution
through a semi-permeable (partially Net movement of water molecules
permeable) membrane. It is regarded Figure 3.2: Movement of water molecules
as a special form of diffusion because during osmosis
it involves the movement of water
molecules through a semi-permeable Activity 3.2: Demonstrate osmosis
membrane. In osmosis, water molecules using a cellophane membrane

move from a low concentrated solution Materials
into a high concentrated solution through
a semi-permeable membrane, as shown Cellophane membrane, beaker, sugar
in Figure 3.2. The partially permeable solution, water, thistle funnel, and a
membrane is only permeable to water. clamp
For osmosis to take place, there must Procedure
be two solutions separated by a semi- 1. Using a rubber band, tightly cover

permeable membrane. One solution the open end of a thistle funnel
should have a greater volume of water with cellophane membrane.
and a lesser quantity of solute than

66 Student’s Book - Form Two

05/10/2024 15:36:24
BIOLOGY FORM 2 NEW.indd 66 05/10/2024 15:36:24
BIOLOGY FORM 2 NEW.indd 66