Transcript CELL MEMBRANE - Farmingdale Schools

CELL (PLASMA) MEMBRANE
FLUID-MOSAIC MODEL FIRST DE TERMINED
BY S.J. SINGER
The current best model of what a cell
membrane looks like is in the figure
below. As you can see it is made up of
two parts. They are the phospholipids
(magenta and green), the proteins (orange
and red), and the carbohydrates (black).
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Phospholipid bilayer
The heads of the
PHOSPHOLIPIDS are
composed of glycerol and
a phosphate group and like
to dissolve in water.
The tails of the
PHOSPHOLIPIDS are mostly
fatty acids made up of long
carbon and
hydrogen chains. Carbon and
hydrogen chains are not polar
and do not like to dissolve
in water.
Passive Transport DIFFUSION
Diffusion is the movement from a high
concentration of molecules to a low
concentration of
molecules. Molecules can diffuse
across membranes through the
phospholipid bilayer or using a
special protein (facilitated
diffusion). Either kind of diffusion
does NOT need energy from the cell.
Some special proteins move certain
molecules across cell membranes only
with the help of cell energy (either directly
or indirectly).
DIFFUSION
OSMOSIS
 When water diffuses,
the process is called
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).
LYSIS OF A RED BLOOD CELL
TURGID ELODEA CELLS
EFFECTS OF OSMOSIS ON ANIMAL &
PLANT CELLS
If the concentration of solute
(salt) is equal on both sides, the
water will move back and forth
but it won't have any result
on the overall amount of water
on either side.
"ISO" means the same
 The word "HYPO" means less, in
this case there are less solute
(salt) molecules outside the cell,
since salt sucks, water will move
into the cell.
 The cell will gain water and grow
larger. In plant cells, the central
vacuoles will fill and the plant
becomes stiff and rigid, the cell
wall keeps the plant from bursting
 In animal cells, the cell may be in
danger of bursting, organelles
called CONTRACTILE
VACUOLES will pump water out
of the cell to prevent this.
The word "HYPER" means more,
in this case there are more solute
(salt) molecules outside the cell,
which causes the water to be
sucked in that direction.
In plant cells, the central vacuole
loses water and the cells shrink,
causing wilting.
In animal cells, the cells also
shrink.
In both cases, the cell may die.
This is why it is dangerous to drink
sea water - its a myth that drinking
sea water will cause you to go
insane, but people marooned at
sea will speed up dehydration (and
death) by drinking sea water.
Water will move in the direction where there is a high
concentration of solute (like salt) and hence a lower
concentration of water.
ACTIVE TRANSPORT
 Active Transport - this type of transport
requires that the cell use energy, because
substances are moving against the
concentration gradient.
 Endocytosis - cell takes in small & large
particles. Ex. Pinocytosis & Phagocytosis
 Exocytosis - cell gets rid of particles, opposite
of endocytosis
------------------------------------------------------------- CYCLOSIS- Circulation or streaming of the
cytoplasm. Ex. Chloroplasts
Cyclosis of chloroplasts
Moving molecules
with cell energy
is called active
transport. The
cell energy is the
ATP made in the
mitochondria.