Transcript Diffusion Through a Cell Membrane

DIFFUSION
• Food, water, and
other substances
are made of
different kinds of
particles, such as
molecules and
ions.

Particles are
always moving,
like dancers on a
crowded dance
floor.
• You can tell how
particles will tend to
move if you know
how crowded they
are.
• Concentration refers
to how crowded
particles are.
A juice concentrate is a
very strong form of
juice. It has many more
juice particles than
regular juice does.
When
you
mix
the
• In a concentrate, the
concentrate with
juice particles are very water, the juice
crowded.
particles spread out in
the water.
•They tend to move
away from places where
they are concentrated
Thus,
the particles
become less
concentrated.
Particles will
continue to move
from areas of high
concentration to
areas of low
concentration until
they reach
equilibrium.
•This process is called diffusion.
• Watch the demonstration with food coloring
in water, then answer the following:
Explain
why the ink spreads out in the water.
Use the words concentration and diffusion in your
answer.
The dye is very concentrated when it enters the
water. The dye diffuses through the water to
lower concentrated areas until equilibrium is
reached.
Diffusion Through a Cell Membrane
• Cells also need food
and water to live
• Substances move
into and out of the
cell through its cell
membrane
• A cell membrane is
like the cell’s skin.
•Just as ink diffuses in
water, some
substances can
diffuse into and out of
a cell through its cell
membrane.
•Particles of some
substances can
diffuse through
proteins in the cell
membrane.(facilitated
diffusion)
• Diffusion is an important process that
allows a cell to get substances it
needs.
• Complete the Vocabulary Review on
your note sheet.
Reviewing Vocabulary
1. Some substances move into and out of cells
by diffusion.
2. The word concentration refers to how
crowded particles are.
3. Some particles diffuse into and out of cells
through the cell membrane
4. Particles tend to move toward places where
they have a low concentration.
5. Particles tend to move away from places
where they have a high concentration
6. Give one example of diffusion in your home.
cooking, sugar in tea, ‘cut the cheese’
OSMOSIS
• Most of your body
is made of water.
• This water can
move into and out
of your cells
• Water can enter
and leave your
cells by diffusion.

When water
DIFFUSES
through a CELL
MEMBRANE, the
process is called
OSMOSIS.
In
the picture, water is diffusing through a cell membrane.
Water particles
Outside of Cell
Cell
Membrane
Inside of Cell
Why
is the water moving INTO the cell in the picture?
• Because water has a lower concentration
inside the cell than outside the cell.
• Water moves into the cell by OSMOSIS.
• What happens to the raisin after sitting
in the water for a while?
It
becomes larger
Why
does this happen?
• Water molecules have a lower concentration
inside the raisin. Outside the raisin, water
molecules are crowded. Water molecules
diffuse into the raisin by osmosis.
PASSIVE TRANSPORT
• Cells do not use energy
to move particles by
osmosis or diffusion
• Particles move freely
into and out of cells.
This kind of movement
is called PASSIVE
TRANSPORT

Complete the
Vocabulary
Review.
Diffusion, Osmosis and facillitated diffusion are
all types of passive transport
Vocabulary Review
1. One example of osmosis is water diffusing into a
raisin.
2. Cells do not work to move molecules by passive
transport.
3. Two forms of passive transport are osmosis and
diffusion.
4. In diffusion and osmosis, particles move by
themselves.
5. Water molecules tend to move to places where they
have a low concentration.
6. Give one way that osmosis is similar to diffusion.
Both move from high to low concentration.
Active vs. Passive Transport
• Passive Transport –
does not require
energy. Particles
move from high to low
concentration.
• Active Transport –
does require energy
because molecules
are moving from low
to high concentration
Endocytosis
• Some things the
cells needs are
too large to pass
through the cell
membrane.
• The cell
membrane can
surround a large
particle located
outside the cell.

The membrane forms a
sac around the particle.

Then the sac opens
inside the cell.
Large particle leave the
cell in sacs too.
Inside a cell, a sac forms
around large waste
particles.
• The sac moves to the
membrane and then
opens outside the cell.
• Waste particle move
OUTSIDE the cell.
• This process of moving
large particles OUT of
the membrane is called
EXOCYTOSIS.
Cells Maintain Balance
• The cell controls its food and water content
by moving ions, molecules, and larger
particles into or out of itself. This is how the
cell maintains homeostasis.
• Homeostasis Simulation
http://trc.ucdavis.edu/biosci10v/bis10v/media/c
h17/hot_guy.html
• Complete the Vocabulary Review
Vocabulary Review
1. Cells use energy to move molecules by active
transport.
2. Diffusion and osmosis are two kinds of
passive transport.
3. Some molecules are too large to pass through
the cell membrane.
4. Cells take in large molecules by endocytosis.
5. Cells must maintain a balance, called
homeostasis.