Download cell membrane - Fort Bend ISD

Cell Boundaries
TAKS Objective 2
The cell membrane
All living cells have
cell membranes
The cell membrane
(plasma membrane)
regulates what enters and
leaves the cell and
provides protection and
support (helps the cell
maintain homeostasis).
Cell membrane
• The cell membrane is
made of a double layer
of phospholipids, called
a lipid bilayer.
• Polar heads make up the
exterior of the lipid
bilayer and the interior
is made of it’s nonpolar
tails.
• It contains proteins
which helps certain
materials enter and exit
the cell.
Cell Membrane in action
Click on the following link and scroll down
to the The Fluid Quality of Membranes
portion and show the animation (click
begin)
http://telstar.ote.cmu.edu/biology/downloads/
membranes/index.html
Diffusion (Passive Transport)
• Diffusion causes many
substances to move across
a cell membrane but does
not require the cell to use
energy.
• Diffusion occurs from a
higher concentration to a
lower concentration until
equilibrium is established.
Osmosis (Passive Transport)
• Osmosis is the diffusion of
water through a selectively
permeable membrane (selects
which materials can enter or
exit the cell)
• Is water the solvent or solute?
• http://www.tvdsb.on.ca/westmi
n/science/sbi3a1/Cells/Osmosis
.htm
Osmosis in Action
The direction of water movement across the cell membrane depends on the relative concentrations of free
water molecules in the cytoplasm and in the fluid outside the cell. There are three possibilities for the
direction of water movement
• Hypotonic solution have
less solute than water
(dilute). Water will flow
into a cell, causing the cell
to swell.
• Isotonic solutions have
equal concentrations of
solute and water. Water
will flow in and out of the
cell at an equal rate
• Hypertonic solutions
have more solute than
water (concentrated).
Water will flow out of the
cell, causing the cell to
shrink
Facilitated Diffusion
(passive transport)
• In facilitated diffusion,
molecules, such as
glucose, that cannot
diffuse across the cell
membrane’s lipid
bilayer on their own.
They must move
through the cell
membrane with the help
of carrier proteins.
Active Transport
• Active transport is a
process that moves
material across a cell
membrane against a
concentration difference
(from low to high) and
requires transport
protein and energy
(ATP).
• Example: transport of K,
Na, Ca ions.
Active Transport
• Endocytosis
(moving into the
cell) and
• Exocytosis (moving
out of the cell) are
also other forms of
active transport.