How does the process of diffusion
and the structure of the cell
membrane help the cell maintain
homeostasis?
What is diffusion?
The net movement of
particles from where
they are more
concentrated to
where they are less
concentrated.
What do we mean by concentration?
The amount of a substance
It’s all about
concentration
The reason
diffusion occurs
is because
molecules are
always…
MOVING
Why are particles always moving?
ENERGY
Particles are in constant motion
because they have energy
What is the end result of diffusion?
The number of particles are now
evenly distributed….
This is called: Dynamic Equilibrium
Dynamic Equilibrium
At this point, the number of particles have spread
themselves out equally throughout the beaker.
Are the particles still moving after dynamic
equilibrium has been reached?
YES
An illustration of diffusion:
Two Conditions for Diffusion:
1)There must be a concentration
gradient
2) There must be no barrier blocking
the movement of particles.
What is a concentration gradient?
The difference in concentration
between a region of high
concentration and a region of
lower concentration.
Does this picture
illustrate a concentration
gradient?
Identify which pictures illustrates a
concentration gradient.
What do we mean by a barrier?
Will diffusion take place?
YES
Will diffusion take place
now? NO
The particles must be free to move
down their concentration gradient in
order for diffusion to occur.
Does diffusion take place across
the cell membrane?
Yes, the cell is:
Selectively Permeable
Cell Membranes are:
Selectively Permeable
A selectively permeable membrane
allows some substances to cross the
membrane more easily than others and
blocks the passage of other substances
altogether.
Why do some things get
through the cell membrane?
Small molecules are more likely to
get through the cell membrane
compared to big molecules
Helping Cells Survive
• Cell membranes must help organism
maintain HOMEOSTASIS by controlling
what substances enter or leave the cells.
• To stay alive, a cell must exchange
materials such as food, water, and waste
with its environment.
What is the main job of the cell
membrane?
• Cell membranes helps organisms
HOMEOSTASIS
& TRANSPORT
maintain
_____________
by
controlling what substances may enter
or leave cells
• To stay alive, a cell must exchange
materials such as food, water, &
wastes with its environment
The diagram to the right represents a portion of a
cell membrane.
Which structure may function in the recognition
of chemical signals? (1) A (3) C (2) B (4) D
Two molecules, A and B, and their distribution
inside and outside of a cell are represented in the
diagram to the right.
• State one possible reason why molecule A
could diffuse across the membrane of the cell
but molecule B could not.