2. Semi-Permeable
Membrane
 The cell membrane
is semi-permeable
 Semi-permeable-
only certain things
can pass through
(permeate) it
 Smaller molecules
can pass through.
 Larger molecules
and charged
molecules cannot.

3. Passive vs. Active Transport
 PASSIVE= **No energy (ATP) needed for
movement of certain particles across the
membrane in/out of cell.
 Particles (molecules and ions) move from
HIGH to LOW concentration.
 “Paddling with the current.”
 Types of passive transport
Diffusion
Osmosis

4. Diffusion
 Move from high to low
concentration
 Occurs until equilibrium is
reached.
 PASSIVE TRANSPORT, SO NO
ENERGY REQUIRED FOR
PARTICLES TO DIFFUSE!!!

5. Osmosis
 Osmosis-diffusion
of water
 PASSIVE, SO NO
ENERGY
REQUIRED TO DO
THIS!
 Water can go
through the semi-
permeable cell
membrane.
 High  low

6. Hypertonic Environments
 Osmosis can occur with water
going into OR out of the cell,
depending on what type of
environment the cell is in.
 Hyper= above/higher
 Hypertonic- the cell is in a higher
solute concentration
 i.e. saltwater
 Osmosis- water moves OUT
of cell in this environment
(highlow).
 Shrivel and die.

8. Plasmolysis
 Occurs when plant cells lose
water in hypertonic environment.

9. Hypotonic Environments
 Hypo = under/lower
 Hypotonic- the cell is in a
lower solute concentration
 i.e. pure water
 Osmosis- water will move
INTO cell in this
environment (highlow)
 Swells with water and bursts.

11. Osmotic Pressure
 The pressure that builds up inside a cell
due to a hypotonic environment (i.e. pure
water.)
 If pressure is too high, what happens?
 Osmotic pressure in plants = turgor
pressure.
 Cell wall prevents plant cells from bursting
—like a water balloon in a box

12. Isotonic Environments
 Iso = same/equal
 Isotonic cell environment-
equal solute concentration
inside and outside the cell
 i.e. pure blood
 Water flow in = water flow out
 Cells remain the same

13. 98% Water, 2% Salt 98% Water, 2% Salt
98% Water, 2% Salt
96% Water, 4% salt 100% Water, 0% Salt 98% Water, 2% Salt
Concentrated Saltwater Pure Water Blood