Laboratory Activity 4
Diffusion and Osmosis
Introduction:
To stay alive, a cell must allow certain materials to enter or exit from
it. This movement of materials generally proceeds along a concentration
gradient. All substances that move into and out of the cell pass through a
semipermeable membrane.
There are two general mechanism of membrane transport: passive
and active. Passive transport involves the movement of substances from a
region of greater concentration to one of lesser concentration without the
expenditure of cellular energy. This may be through either simple diffusion or
facilitated diffusion. Active transport, on the other hand, is the movement of
substances from a region of lesser concentration to a region of greater
concentration – a process which requires energy.
Objectives:
After working on this exercise, you should be able to:
a. define diffusion, osmosis, and active transport
b. relate the concepts of diffusion and osmosis to the survival of living
cells.
OSMOSIS IN LIVING TISSUES
Materials:
Potatoes, water, petri-dish (plates), salt, sugar.
Procedure:
1. Cut three potatoes into half and scoop out some material from the center
to make a cavity in each half.
2. place three potato halves in boiling water for 2-3 few minutes to kill the
cytoplasm.
3. place each half of 6 potatoes in plates three-fourths of which is filled with
tap water.
4. for potato 1, place half teaspoon of salt in the cavities of the raw and the
boiled halves. Using sugar, do the same for potato 2. Potato 3 will serve as
your control group.
5. observe the potatoes after 2-3 hours.
