Cell Membranes
Including:
Diffusion
Osmosis
Facilitated Diffusion
Active Transport
Endo-, Pino-, and Exo- cytosis
Cell Membrane
• Also called the plasma membrane, or
"phospholipid bilayer"
• Is a selectively permeable lipid bilayer found
in all cells.
– Selectively permeable means some molecules are
allowed to go through and some are not.
• It contains a wide variety of biological
molecules, primarily proteins and lipids,
which are involved in a vast array of cellular
processes
Phospholipids…
…are like fats except it has a phosphate
group in place of the fatty acid. This means
that phospholipids have a hydrophilic head
and hydrophobic tail and this is important
because phospholipids self assemble in
water into a bi-layer.
Fluid Mosaic Model
Diffusion
• The process by
which molecules
spread from areas of
high concentration, to areas of low
concentration.
• No energy is required
• When the molecules are even throughout
a space - it is called EQUILIBRIUM
Diffusion across a membrane
Osmosis
• Osmosis is the
diffusion of water
through a selectively
permeable membrane
down its concentration
gradient
• From an area of high
water concentration
to an area of lower
water concentration
Osmotic Pressure
The pressure required to prevent the passage
of water through a semi-permeable
membrane from a region of low concentration
of solutes to one of higher concentration, by
osmosis.
Cell walls create this
pressure this prevents
plant cells from
breaking
Isotonic Solution
• A solution that has the same
salt concentration as the
normal cells of the body and
the blood.
Hypertonic Solution
• A solution with a higher salt
concentration than in normal cells
of the body and the blood
Hypotonic Solution
• A solution with a lower salt
concentration than in normal
cells of the body and the
blood.
Facilitated Diffusion…
…is the spontaneous passage of
molecules or ions across a biological
membrane passing through specific
membrane transport proteins.
Active transport…
– requires energy
– Uses membrane proteins
– Goes from area of low concentration to
an area of high concentration
Endocytosis…
…is the process by which cells absorb
material (molecules such as proteins) from
outside the cell by engulfing it with their cell
membrane
• Two Types
– Pinocytosis
– Phagocytosis
Pinocytosis
• Movement of
liquids into
the cell
Phagocytosis…
movement of
solids into
the cell
Exocytosis
• …is a cellular process where cells eject
waste products or chemical
transmitters (such as hormones) from
the interior of the cell.
• Exocytosis is similar
in function to
Endocytosis but works
in the opposite
direction.