Transcript Cell Membranes, Diffusion, and Osmosis

Cell Membranes and Membrane Transport
Cell Membrane
1.
Functions
A. Holds in contents
B. Regulates what goes in
and out of cell
2.
Main Structure
A. Made of phospholipids
i.
ii.
Phosphate head
(hydrophilic),
Fatty acid tail
(hydrophobic)
B. Forms a “bilayer”
Cell Membrane
3.
Other Structures
A. Cholesterol- keeps the phospholipids from
locking together
B. Proteins- helps move things across the
membrane
C. Carbohydrates- helps cells identify each other
Membrane Transport
1.
Solute/Solvent/Solution
A. Solute: molecule being dissolved (example: salt)
B. Solvent: molecules doing the dissolving (example:
water)
C. Solution: the two together
Membrane Transport
2.
Diffusion
A. Random movement of particles from high
to low concentration
B. Only occurs if there is a concentration
gradient
C. Will continue until equilibrium is reached
(even distribution)
Concentrated, dense
Not concentrated, spread out
Evenly distributed (equilibrium)
Membrane Transport
2.
Diffusion (cont’d)
D. Example: perfume in
corner of room
E. Does not take any
added energy to
happen
F. Facilitated diffusion
needs to use a
protein in the
membrane to
happen
Membrane Transport
3.
Osmosis
A. Diffusion of water through a selectively permeable
membrane
i.
Membrane will only let water through (ONLY WATER CAN
MOVE to equalize things!!!)
B. Very important in cells!
Type of
solution
Distribution
of solute
Isotonic Solution
Equal amount of solute
inside and outside cell
Hypertonic Solution
(hypotonic cell)
More solute outside cell
than inside
Hypotonic Solution
(hypertonic cell)
Less solute outside cell
than inside
Over time, cell will
grow because water
goes in to equalize
concentration
-Animal cells explode!
-plants cells happy (cell
wall is tough enough!)
Drawing
How does
the cell
change?
Over time, nothing
happens
Over time, the cell will
shrink because water goes
out to equalize
concentration
Animal vs
plant cells
-Animals cells happy
-Plant cells wilted
-Animals cells shrink, still ok
-Plant cells tear away from
cell wall, not ok

Animals vs Plant Cells
Membrane Transport
4.
Active Transport
A. Goes against the
concentration
gradient
i.
(As opposed to
diffusion and facilitated
diffusion)
B. Therefore, needs
energy to pump
molecules across the
cell membrane
i.
(As opposed to
diffusion and facilitated
diffusion)
C. Uses membrane
proteins