Download Transport thru the Cell Membrane

Passive
Transport
Fluid Mosaic Model
Review: Why do they call it the FLUID
MOSAIC model for the Cell Membrane?
What would you rather do?
Roll down a hill?
Or
Run up a hill?
Which one would require less energy?
Passive Transport
Does not
expend cellular
energy for the
movement to
take place
Ex-rolling
down a hill
Parts of a Solution
Solute:
what gets dissolved
Solvent:
What does the dissolving, more
plentiful that solute
Solution:
the mixture of solutes and solvent
Example: H2O and NaCl
Solute: NaCl
Solvent: H2O
Solution: H2O and NaCl
3 types of Passive Transport:
1. Diffusion
2. Osmosis
3. Facilitated Diffusion
1. Diffusion
Passive Transport WITHOUT a
Membrane
I. DIFFUSION:
Definition:
Transport of molecules (of solutes
and solvents)
From an area of higher
concentration to an area of lower
concentration
Until equal distribution of
concentrations reached in all areas
(EQUILIBRIUM)
Due to the random movement of
molecules
How does this demonstrate the
properties listed in the previous slide?
Diffusion: Without a Membrane
Osmosis: With a Membrane
Review: What are the three
possible types of membranes?
1. Permeable
2. Impermeable
3. Semi-permeable
ALL types of
molecules can
get through,
regardless of size
or charge.
NO molecules
can get through
Some molecules
can get through
– very small or
non-charged.
Osmosis and Facilitated
Diffusion
Passive
Transport
WITH a
membrane
II.
OSMOSIS:
Definition:
Diffusion through a membrane:
Movement of H2O
from to high to low concentration
THROUGH A MEMBRANE
until DYNAMIC equilibrium is reached
II.
OSMOSIS:
II.
OSMOSIS:
U-tube Osmosis
How do you get different
concentrations of water (2 ways)?
1. Change the amount of solute or
solvent
2. Add a membrane
3 Types of Solutions
(outside of cell):
1. Hypertonic
2. Hypotonic
3. Isotonic
1.Hypertonic:
Hyper =
“above, over,
more”
More solute,
less solvent
(H2O) outside
of the cell
2. Hypotonic:
Hypo = “under,
less”
Less solute,
more solvent
outside of the
cell.
Which way will the water move?
Hypertonic
90% water
80% water
Hypotonic
80% water
90% water
3. Isotonic:
Iso = “EQUAL”
Equal amounts of solute/solvent
concentrations on both sides of
membrane
(a)
Isotonic
Water concentration inside the
cells is equal to the water
concentration in the fluid
surrounding the cell. Therefore,
there is no net movement of
water either into or out of the
cell.
(b)
Hypertonic
Water concentration in the
surrounding medium is lower
than it is in the cell. Water
moves out of the cells and the
cells shrivel (crenate).
(c)
Hypotonic
Water concentration outside
the cell is greater than it is
inside the cell. Water moves
into the cell, which swell and
sometimes burst – a process
called lysis.
Consequences (of Solution Concentration):
Hypertonic  Cell Shrinking
In a plant cell: PLASMOLYSIS
In an animal cell: CRENATION
(Shriveled)
Examples:
Drinking out of ocean when you are
dying of thirst or 
Placing a fresh water fish or plant in
salt water… 
Plant Wilting sue to lack of water 
Consequences (of Solution Concentration):
(a)
Isotonic
Water concentration inside the
cells is equal to the water
concentration in the fluid
surrounding the cell. Therefore,
there is no net movement of
water either into or out of the
cell.
(b)
Hypertonic
Water concentration in the
surrounding medium is lower
than it is in the cell. Water
moves out of the cells and the
cells shrivel (crenate).
(c)
Hypotonic
Water concentration outside
the cell is greater than it is
inside the cell. Water moves
into the cell, which swell and
sometimes burst – a process
called lysis.
Consequences (of Solution Concentration):
Hypotonic  Cell Expanding
In a plant cell: TURGID (Firm)
In an animal cell: CYTOLYSIS
(Lysed: Cell Bursting)
Examples:
Place a salt water fish in fresh
water 
Red Blood Cells in pure water
Plants standing tall after
being watered
Osmotic Pressure = Turgor Pressure
As a result of osmosis, extra
water molecules accumulate
on one side of membrane and
cause pressure on the
membrane
 “Turgor”
Example: plant cell
water
Normal
Cytolysis
Crenation
Flaccid
Turgid
**Normal**
Plasmolyzed
III. FACILITATED DIFFUSION:
Protein Channels in the cell membrane
accept only specific molecules, like a lock
accepts a particular key.
III. FACILITATED DIFFUSION:
Many of these protein channels are
“two-way” and are called PORES.
These transport ions or molecules
(solutes) through membranes in
either direction
III. FACILITATED DIFFUSION:
Like an open door allows you to pass
into or out of a room.
Different solute molecules fit different
pores
This depends on
Size
Polarity
Shape of molecule
Eg. Glucose
III. FACILITATED DIFFUSION:
When a solute that is
plentiful on one side
of membrane,
they will pass by
diffusion toward other
side with the lower
concentration.
Until concentration
becomes equal on
both sides
DON’T FORGET,
These were all
PASSIVE TRANSPORT
–SO THE CELL DID NOT NEED TO
EXPEND ANY ENERGY TO MAKE IT
HAPPEN!!!!!