Download The Cell Membrane

Bell Work
 Get out your Photosynthesis Cell
Respiration Lab
 Open to the conclusion page (Part II)
 On a blank sheet of paper write down:
 Your name and your partner’s name for the cell
project
 What you are planning on doing for the cell project
 How far along you are with the cell project
 How long you think your presentation will take
And the Effect of Osmosis on the Cell
Diffusion
 Molecules move from an area of high concentration
(where there are lots) to areas of lower concentration
(where there are few)
 Diffusion requires no energy because it happens
naturally
 When the areas have the same concentration the
solution is in equilibrium. Molecules are still moving
around, but equally in both directions.
 http://www.indiana.edu/~phys215/lecture/lecnotes/di
ff.html
Osmosis
 The diffusion of water molecules through a selectively
permeable membrane (like the cell membrane)
 Water
molecules move
freely back and
forth across the
membrane, but
other molecules
cannot
Selective Permeability
 Some molecules can cross the
membrane, but others cannot
 Typically the molecules that can cross
are small uncharged ones (like water)
and the ones that cannot cross are
large (like sugar) or very charged
molecules (like ions)
Osmosis and the Cell Membrane
 When you have a high concentration of molecules that
cannot penetrate the membrane on one side of a
membrane more water will flow to that side to even
out the concentrations.
 http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/a
nimation__how_osmosis_works.html
Osmotic Pressure
 The pressure exerted by the water molecules on the
membrane.
 Hypotonic – when water is moving into the cell pressing
the membrane outward.
 This is a high osmotic pressure
 It may cause the cell to lyse or burst
 Usually occurs in fresh water
 Hypertonic – when water moves out of a cell
 This is a low osmotic pressure
 The cell will shrink and shrivel up
 Occurs in high concentration solutions
 Isotonic – When the water is moving equally in both
directions causing no osmotic pressure
Cell Membrane
 Regulates what enters and leaves the cell and by doing so
provides protection and support.
 The cell membrane
is made up of a lipid
bilayer with proteins
embedded in it. These
proteins many times
have carbohydrate
chains attached to
their outer surfaces.
The Lipid Bilayer
 Lipids have a
hydrophobic (water
hating) tail and a
hydrophilic (water
loving) head.
 The bilayer forms so
that all of the
hydrophobic tails can be
away from the water and
the heads face outwards
towards the water.
Channel Proteins
 These proteins facilitate diffusion by creating open channels
which allow specific molecules to pass right through it
 There is no energy required because the molecules will travel
naturally according to concentrations outside and inside the
c
cell
 This is called facilitated diffusion
Protein Pumps
 These proteins will
move specific
molecules across the
cell membrane
against their
concentration
gradient (from a
lower to higher
concentration)
 This is called active
transport because
they require energy
Sodium Potassium Pump
Endocytosis
 When the cell
surrounds some
molecules and folds
inward. The cell
membrane fuses
together cutting off
the in-pocket with
it’s contents
creating a vacuole.
Exocytosis
 The removal of large amounts of material from the cell that
occurs from a vacuole fusing with the cell membrane and
releasing its
contents out of
the cell