Patterns in Nature
Compare the processes of diffusion and
osmosis
perform a first-hand investigation to
demonstrate the difference between osmosis
and diffusion
perform a first-hand investigation to model
the selectively permeable nature of a cell
membrane
Diffusion and Osmosis
The processes of diffusion and osmosis
account for much of the passive
movement of molecules at the cellular
level.
DIFFUSION
Molecules are in constant motion
Movement tends to be from high
concentration to areas of low
concentration. Diffusion is the net
movement of molecules down their
concentration gradient. Diffusion
can occur in gases and in liquids.
OSMOSIS
Osmosis is a specialized case of
diffusion that involves the
passive transport of water. In
osmosis water moves through a
selectively permeable membrane
from a region of its higher
concentration to a region of its
lower concentration.
LETS TAKE A CLOSER LOOK
MOVEMENT OF MOLECULES IN SOLUTION
There are several different types of molecules in a solution
Movement of each molecule is random and independent of other molecules
in a solution
Each molecule moves down its own concentration gradient from a region of
its HIGH concentration to a region of its LOW concentration.
Common misconception is that this is the only way for molecules to move.
Although the net movement of molecules is down their concentration
gradient, at any time molecules can move in both directions as long as the
membrane is permeable to the molecule.
Concentration gradient
Perform a first hand investigation to demonstrate
the difference between osmosis and diffusion.
Aim:
Experiment A: To observe the process of osmosis using a unboiled potato
and a boiled potato.
Experiment B: To observe the process of diffusion using coloured dye.
Materials:
Experiment A:
Unboiled potato
Boiled potato
Spatula
Table salt
Water
2 Petri dishes
Experiment B:
Beaker
Water
Coloured dye
Perform a first hand investigation to demonstrate
the difference between osmosis and diffusion.
Method:
Experiment A:
1. Using a spatula make a hole in the middle of the unboiled and boiled
potato. Make sure not to reach the base of potato, however still deep. Put
aside.
2. Fill the two petri dishes with ¾ of water.
3. Place the unboiled potato and boiled potato in the middle of each petri
dish.
4. Add half a teaspoon of salt into each hole of the unboiled and boiled
potato.
5. Leave aside for 10 minutes. Start experiment B.
Perform a first hand investigation to demonstrate
the difference between osmosis and diffusion.
Method:
Experiment B:
6. Collect a beaker, fill it with water. Do not overflow.
7. Add a few drops of dye into the beaker.
8. Observe the beaker for about 3 minutes, note what is happening.
9. Once finished with the beaker, observe the rested potato, note
any changes.
Let’s blog it out
http://osmosisdiffusion.wordpress.com
Types of solutions based on solute
concentration
In the illustration, the solution in the
bag contains less solute than the
solution in the beaker. The solution in
the bag is hypotonic (lower solute
concentration) to the solution in the
beaker. The solution in the beaker is
hypertonic (higher solute
concentration) to the one in the bag.
Water will move from the hypotonic
solution into the hypertonic solution.
In this illustration the two
solutions are equal in their
solute concentrations. We say
that they are isotonic to each
other.
Water potential
Because you will be working with potato cells
in the laboratory, you need to understand the
concept of water potential. Biologists use this
term to describe the tendency of water to
leave one place in favour of another. Water
always moves from an area of higher water
potential to an area of lower water potential.
Water potential is affected by two factors:
pressure and the amount of solute. For
example, imagine a red blood cell dropped
into distilled water. Water will move into the
red blood cell and cause the cell to expand,
stretching the flexible membrane. At some
point, the pressure of the incoming water will
cause the cell to pop, just like an over-filled
balloon.