Download Diffusion and Osmosis

DIFFUSION AND
OSMOSIS
The Cell Membrane
ABOUT CELL MEMBRANES
All cells have a cell membrane
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.
TOO BIG TO PASS
THROUGH THE
MEMBRANE
PASSIVE TRANSPORT BY PROTEINS
 Some
transport proteins, called channel
proteins, form channels that allow specific
molecules to flow through.
ABOUT CELL MEMBRANES (CONTINUED)
Structure of cell membrane
Lipid Bilayer -2 layers
of phospholipids
a. Phosphate
head is polar
(water loving)
b. Fatty acid tails nonpolar (water fearing)
c. Proteins embedded in
membrane
Phospholipid
Lipid Bilayer
Polar heads Where would you
love water & be least likely to
dissolve.
find water in the
cell membrane?
Non-polar
tails hide
from water.
Carbohydrate cell
markers
Proteins
ABOUT CELL MEMBRANES
(CONTINUED)

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
A cells contents would be the same as its
surroundings without selective permeability
Structure of the Cell Membrane
www.teachertube.com/viewVideo.php?video_id=144202&title=Cell_membrane
Outside of cell
Proteins
Lipid
Bilayer
Transport
Protein
Go to
Section:
Carbohydrate
chains
Phospholipids
Inside of cell
(cytoplasm)
What macromolecule helps move molecules
Through channels or pumps?
Proteins
What keeps tails from sticking together?
Cholesterol
Which macromolecule stick out from the
cell
And act like ID cards to identify other
cells?
Carbohydrates
TYPES OF CELLULAR
TRANSPORT

Passive Transport
cell doesn’t use energy
1.
2.
3.

Weeee!!!
Diffusion
Facilitated Diffusion
Osmosis
high
low
Active Transport
cell does use energy
1.
2.
3.
Protein Pumps
Endocytosis
Exocytosis
This is
gonna be
hard
work!!
high
low
PASSIVE TRANSPORT

cell uses no energy
molecules move randomly
Molecules spread out from an
area of high concentration
to an area of low
concentration.

(HighLow)

Three types:


3 TYPES OF PASSIVE
TRANSPORT
1.
2.
3.
Diffusion
Facilitative Diffusion –
diffusion with the help of
transport proteins
Osmosis – diffusion of
water
PASSIVE TRANSPORT:
1. DIFFUSION
1.
Diffusion: random movement of
particles from an area of high
concentration to an area of low
concentration.
(High to Low)

Diffusion continues until all
molecules are evenly spaced
(equilibrium is reached)-Note:
molecules will still move around
but stay spread out.
http://bio.winona.edu/berg/Free.htm
EXAMPLE OF DIFFUSION
Smell of cookies baking in the
oven
Diffusion occurs because molecules constantly
move and collide with one another
PASSIVE TRANSPORT BY PROTEINS

Plasma
membrane
Passive transport of materials across the
membrane using transport proteins is called
facilitated diffusion.
Channel proteins
Concentration
gradient
Passive Transport:
2. Facilitated Diffusion
A
B
Facilitated
diffusion
(Channel
Protein)
Diffusion
(Lipid
Bilayer)
2. Facilitated diffusion:
diffusion of specific
particles through
transport proteins found
in the membrane
Transport Proteins are specific
– they “select” only certain
molecules to cross the
membrane
b. Transports larger or charged
molecules
a.
Carrier Protein
Passive Transport: 2. Facilitated Diffusion
Glucose
molecules
Cellular Transport From aHigh Concentration
High
Cell Membrane
Low Concentration
Through a 
Go to
Section:
Transport
Protein
Protein
channel
Low
Passive Transport:
3. Osmosis
 3.Osmosis:
diffusion
of water through a
selectively permeable
membrane
 Water moves from
high to low
concentrations
•Water moves freely
through pores.
•Solute (green) to large
to move across.
WHAT CONTROLS OSMOSIS?
 Unequal
distribution of
particles,
called a
concentratio
n gradient, is
one factor that
controls
osmosis.
Before
Osmosis
After
Osmosis
Selectively
permeable
membrane
Water molecule
Sugar molecule
Three solutions
ISOTONIC SOLUTION
Isotonic: The concentration of solutes in the solution is
equal to the concentration of solutes inside the cell.
Result: Water moves equally in both directions and the cell
remains same size! (Equilibrium)
Isotonic- water moves in
and out of cell in
equilibrium
CELLS IN AN ISOTONIC SOLUTION
water
H2O
H2O
Water
Molecule
Dissolved
Molecule
molecules move
into and out of
the cell at the
same rate, and
cells retain
their normal
shape.
CELLS IN AN ISOTONIC SOLUTION
A
plant cell has
its normal shape
and pressure in
an isotonic
solution.
HYPOTONIC SOLUTION
Hypotonic: The solution has a lower concentration of
solutes and a higher concentration of water than inside the
cell. (Low solute; High water)
Result: Water moves from the solution to inside the cell):
Cell Swells and bursts open (cytolysis)!
Hypotonic- water
concentration is
higher outside of the
cell, water enters
and cell swells
CELLS IN A HYPOTONIC SOLUTION
 Plant
cells swell
beyond their normal
size as pressure
increases. (plants
prefer this –it makes
the leaves firm)
HYPERTONIC SOLUTION
Hypertonic: The solution has a higher concentration of
solutes and a lower concentration of water than inside the
cell. (High solute; Low water)
shrinks
Result: Water moves from inside the cell into the solution:
Cell shrinks (Plasmolysis)!
Hypertonic- water
concentration is
higher in the cell than
out- water leaves and
the cell shrinks
CELLS IN A HYPERTONIC SOLUTION
 Plant
cells lose
pressure as the
plasma membrane
shrinks away from
the cell wall.
PLASMOLYSIS
WHAT TYPE OF SOLUTION AM I?
H2O
H2O
Hypertonic
Isotonic
Hypotonic
What type of solution are these cells in?
A
B
C
Hypertonic
Isotonic
Hypotonic
WITH OSMOTIC
PRESSURE
•Bacteria and plants have cell walls that prevent them from
over-expanding. In plants the pressure exerted on the cell
wall is called turgor pressure.
•A protist like paramecium has contractile vacuoles that
collect water flowing in and pump it out to prevent them
from over-expanding.
•Salt water fish pump salt out of their specialized gills so they
do not dehydrate.
•Animal cells are bathed in blood. Kidneys keep the blood
isotonic by remove excess salt and water.