Diffusion
Osmosis
Active Transport
Endocytosis
Exocytosis
This lesson is all about how a
cell can move materials into
and out of itself.
Diffusion is the distribution
of a solute in a solvent from
an area of high concentration
to low concentration, without
adding energy, until a uniform
distribution is achieved.
What is diffusion?
This solution has a
uniform concentration.
Can diffusion occur?
What is diffusion?
This orange dot is an area
of high concentration. What
will happen to it?
Where is the
energy for
diffusion coming
from? How does
the temperature
of the solvent
affect diffusion?
When will
Would this
diffusion
stop?
happen faster
Why?
in a hot solvent
or a cold
solvent? Why?
Observe the molecules of the
“orange dot”. What will happen
to them? What is the process
called?
This is a divided
container. What will
happen when the
separating wall is
removed? Why?
The dotted line
represents a porous
separator
(it has holes in it).
How will that affect
diffusion?
It still diffused,
just as before,
but all other things
being equal,
it took more time.
How is this different?
How will it affect
diffusion?
Osmosis is like diffusion, in that no outside energy is involved and
materials tend to move from high concentration to low concentration,
but it is different in that a membrane is involved which controls to some
degree which things may cross the membrane, so complete mixing may
not occur. A membrane may stop certain things from crossing.
The “bags” represent a membrane. Why did it expand? What was at
lower concentration inside the bag? Did the red dots diffuse out? Why?
Is this cell
membrane
affecting
diffusion of
the red material?
Diffusion occurs
in membranes
through pores,
which act like
simple holes like
in the barrier we
saw before.
Cells can facilitate diffusion of selected
molecules through osmosis.
Why would they want to not be uniform
in their treatment of all their molecules?
In active transport, the cells expend energy
to obtain certain molecules and bring them
inside the cell membrane.
In endocytosis, the cell surrounds
the desired material and grows
around it,until the material
is incorporated into the
cell. This is particularly
helpful for getting large
things that cannot pass
through the pores of the membrane.
Use your knowledge of language arts
and of endocytosis to define exocytosis.
The diagram above shows what is happening.
Analyze this. Why would a cell do this?
Secretion describes the use
of exocytosis by a large
number of cells.