Warm-Up
Imagine if you had to live inside a sealed plastic bag. How
long would you survive? What would be the three main
issues with this?
What is the function of the cell membrane?
Predict what might happen if the cell membrane did not
allow anything in or out.
What is the term that refers to something that does not
allow anything through it?
Diffusion, Semipermeable Membrane,
Osmosis
Cell Membrane
The cell needs nutrients for energy and raw materials (for
growth). As well, the cell needs to get rid of waste products
that are produced inside the cell.
In order for the cell to do this , the cell membrane needs to
allow some materials into the cell, but not others.
For example: When you eat
food, it goes into your
stomach, then into your
intestines. There are many
cells that line the sides of
your intestine. The
digested (broken down)
food passes through the
cell membrane and into
your cell.
Semi-permeable
Membranes
The cell membrane is a selectively permeable membrane.
This means that it has many small openings that let some substances pass
through it but not others.
One way that substances can move through the cell membrane is by
diffusion.
When the concentration on both sides of the membrane is the same, it is
called equilibrium.
Group Demo!
Warm-up
What is common between the three images?
In your own words, define random.
Diffusion
Diffusion is the movement of particles from an area of higher
concentration to an area of lower concentration.
Concentration is the amount of substance in a given space.
The smell of fresh baked bread “spreading” throughout the
room is an example of diffusion.
The diffusion
of dye in
water.
Randomness
Diffusion Animation
Osmosis
Osmosis: the process by
which water moves across
the cell membrane from an
area of high concentration
to an are of low
concentration.
It’s actually a special case of
diffusion (ie. Diffusion of
water molecules)
Water is moving from an
area of high concentration
to low concentration
Problem Solving
In your own words, state the problem that we are we
have observed.
We have a solution of starch solution in dialysis tubing.
These are really big molecules. We submerge this
“package” into a solution of KI (small molecules). We
see that within the dialysis tubing, a colour change
occurs and the contents turn blue. Why did the
solution within the dialysis tubing turn blue and not
the whole beaker of solution?
Brainstorm
Create a web to collect and record anything you think
might possibly help your to come up with solutions
to the problem.
The solution within the tubing needed the
temperature from the KI to activate
KI was able to get into the tubing by the ends
because they were not tied off correctly
There are small pores within the tubing that allows
the small KI to get in but not the big starch to get out
The tubing began to be dissolve in the KI solution
Solution
Suggest solution(s) to the problem
Propose a solution or solutions to the problem you stated and
explain your reasons for choosing that solution.
The KI molecules are small and diffuse through the pores and
into the dialysis tubing. The KI molecules bind (stick) to the
starch molecules causing them to turn blue. The starch
molecules are too big to pass out of the membrane (tubing) so
the blue colour stays inside.
We know this because we understand the concepts of diffusion
and semi-permeable membranes. The KI wants to move from
high concentration in the beaker to low concentration in the
tubing and it is small enough to move through the pores in the
tubing, but the starch is too big to move out.
Example: Dialysis Tubing
with KI and Starch Solution
Your cell membrane is like the dialysis tubing
 It looks like a bag
 It doesn’t seem like it is letting anything in and out, but
it actually has pores! (eg. Tiny molecules can pass
through)
DEMO! – Practice Problem Solving
Say that in the dialysis tubing, there’s a starch solution
(really big molecules). You put it in KI solution (small
molecules), and you see that colour seeps into the
tubing (blue).
Why does this happen?