Transcript Movement through the Membrane

Movement through the
Membrane
Chapter 7-3
Cell Membrane
Regulates what enters and leaves the
cell (kind of like a security guard)
Made of a lipid bilayer
– 2 layers of lipids
– Provides a tough, flexible barrier
between the cell and its surroundings
Proteins and carbohydrates can also
be found in the cell membrane.
Cell Membrane
One of the most important functions
of the cell membrane is to regulate
the movement of molecules from one
side of the membrane to the other.
The cell membrane is selectively
permeable (it doesn’t let just
everything through; it is selective).
Equilibrium
Equilibrium—same concentration
(amount per area) on both sides;
equal
Molecules are constantly moving
across the membrane.
In equilibrium, the molecules are
moving at the same rate.
Isotonic Solution
same strength
same
concentration
as cell
water
molecules
move in and
out at same
rate
Hypertonic Solution
above strength
higher
concentration
than cell
water moves
out of the cell
Hypotonic Solution
below strength
lower
concentration
than cell
water moves
into the cell
4 Types of Movement through
the Membrane
Diffusion
Osmosis
Passive Transport (also called
facilitated diffusion)
Active Transport
Diffusion
Diffusion is the movement of
molecules from an area of high
concentration (crowded) to an
area of low concentration
(uncrowded) until equilibrium is
reached
Diffusion does NOT require the
cell to use energy.
Diffusion
Osmosis
Osmosis is the diffusion of water.
Water moves from high
concentration to low
concentration.
It does NOT require energy.
Osmotic Pressure
Fresh water is ALWAYS
hypotonic to a cell.
Water will move into a cell in
fresh water, causing it to swell
and possibly causing it to burst.
The cell wall prevents the cell
from expanding too much.
Passive Transport
Some molecules cannot cross the
lipid bilayer of the cell
membrane.
Proteins in the cell membrane
act as a channel (path). The
proteins passively allow the
molecules through the
membrane.
High to low concentration
Does NOT require energy
Active Transport
LOW (uncrowded) to HIGH
(crowded) concentration!!!!
Proteins act as pumps and
actively force molecules
through the membrane
Active transport REQUIRES
energy!!!