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AIM: How does the process of diffusion and
the structure of the cell membrane help the
cell maintain homeostasis?
DN: Can all substances move through the cell
membrane? What determines what
substances are able to move through the cell
membrane? Give an example of a substance
that can move through the cell membrane and
an example of a substance that cannot move
through the cell membrane.
HW: Page 198-199 #15,16,26,27
What is diffusion?
The movement of
particles
from an area of high
concentration to an area
of low concentration.
What do we mean when we say concentration?
The amount of a particular substance
The reason
diffusion occurs
is because
molecules are
always…
MOVING
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) concentration gradient
2) 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.
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.
Cell Membranes help organisms maintain
HOMEOSTASIS
By controlling what substances may enter
or leave cells. To stay alive, a cell must
exchange materials such as food, water,
and wastes with its environment.
What is the main job of the cell
membrane?
HOMEOSTASIS & TRANSPORT
• Cell membranes helps organisms
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