Download Diffusion & Osmosis

About Cell Membranes
1. All
cells have a cell
membrane
2.Functions:
a.Controls what enters
and exits the cell to
maintain an internal
balance called
homeostasis
b.Provides protection
and support for the
cell
TEM picture of a
real cell membrane.
About Cell Membranes (continued)
 3.
Cell membranes have pores (holes) in
it
a.Selectively permeable: Allows
some molecules in and keeps other
molecules out
b.The structure helps it be selective!
Pores
Define selectively permeable
membrane
A
membrane that allows only certain
materials to cross it
 Materials pass through pores in the
membrane
Diffusion & Osmosis
Passive Transport
2 ways in which materials
are passed across the cell
membrane
Diffusion
The movement of molecules from a
area in which they are highly
concentrated to a area in which they
are less concentrated.
Active Transport
 REQUIRES
THE CELL TO USE
ENERGY
 REQUIRES THE CELL TO WORK!!!
– When the cell engulfs (eats) food
– When substances are carried into and
out of cells such as potassium, calcium,
and sodium
Types of Cellular Transport

Passive Transport
cell doesn’t use energy
1. Diffusion
2. Osmosis

Weeee!!
!
high
low
Active Transport
cell does use energy
1. Protein Pumps= transport
proteins carry molecules
out of cells
This is
gonna
be hard
work!!
high
low
A diagram of an example of
diffusion
High to Low
Osmosis
The diffusion of water, just water, and
only water across a selectively permeable
membrane.
 Water molecules move from an area
where they are highly concentrated to an
area of where they are less concentrated.
 Cells cannot function properly without
water, therefore, many cellular
movements depend on osmosis.

Define osmosis

Water moves from a high
concentration of water (less salt or
sugar dissolved in it) to a low
concentration of water (more salt or
sugar dissolved in it). This means
that water would cross a selectively
permeable membrane from a dilute
solution (less dissolved in it) to a
concentrated solution (more
dissolved in it).
Define osmosis
Define osmosis

In this picture a red blood
cell is put in a glass of
distilled water (all water
with no salt or sugar in
it). Because there is a
higher concentration of
water outside the cell,
water enters the cell by
OSMOSIS. In this case
too much water enters and
the cell swells to the point
of bursting open. In the
end pieces of cell
membrane are left in the
water.
Why are osmosis &
diffusion important?
Why are osmosis & diffusion
important?
All living things have certain requirements
they must satisfy in order to remain alive
– maintain homeostasis
 These include exchanging gases (usually
CO2 and O2), taking in water, minerals,
and food, and eliminating wastes.
 These tasks happen at the cellular level.
 Molecules move through the cell
membrane by diffusion

Why are osmosis & diffusion
important?
 All
living things have certain
requirements they must satisfy in
order to remain alive. These include
exchanging gases (usually CO2 and
O2), taking in water, minerals, and
food, and eliminating wastes. These
tasks ultimately occur at the cellular
level, and require that molecules
move through the membrane that
surrounds the cell.
Why are osmosis & diffusion
important?
 This
membrane is a complex
structure that is responsible for
separating the contents of the cell
from its surroundings, for controlling
the movement of materials into and
out of the cell, and for interacting
with the environment surrounding
the cell.