Transport Through
Membrane
Plasma Membrane
✦ Surrounds the
cell, controls what
enter/exits the
cell
✦ Selectively
Permeable- allows
certain particles
to pass and
blocks others
✦ “bouncer”
✦ Small items pass
through, large
can not
✦ What enters?
✦ Oxygen, nutrients
✦ What leaves?
✦ Carbon dioxide,
waste
Plasma (cell) Membrane
Structure
✦ 1. Phospholipid
bilayer- two rows
of phospholipids,
tails facing each
other
✦ Water loving on
outside
✦ Water fearing in
middle, staying
together
Membrane Structure cont.
✦ 2. Steroids- fit
between tails of
phospholipids
✦ Cholesterol in
animals cells
✦ Allows the
membrane to stay
fluid and increases
movement of
molecules
3. Carbohydrateslocated on outside
of membrane
4. Proteins✦ Peripheral- located
on the surface of
the membrane
✦ Integralembedded within
the membrane can
go through to
other side
✦ Fluid Mosaicterm used to
describe the
movement of the
membrane, fluidpieces are moving
not stationary;
mosaic- many
pieces
Types of Transport
✦ 1. Passive
✦ 2. Active
✦ Cells are
surrounded by
aqueous solutions
with many
substances
dissolved
✦ Concentration
Gradientdifferences in
concentration of
molecules in a
space
Passive Transport
✦ Movement of
substances
through
membrane
✦ From high to low
concentration
✦ No energy
required
✦ Types of Passive
✦ 1. Diffusion
✦ 2. Facilitated
diffusion
✦ 3. Osmosis
Diffusion
✦ Simplest form of passive transport
✦ Examples- oxygen, carbon dioxide
✦ Equilibrium- state where
concentration is the same, no net
movement
Facilitated diffusion
✦ Movement across membrane that
requires assistance by proteins
because molecules are too large or
have a charge
✦ Examples- Glucose, Cl-
✦ Carrier protein- name of proteins
that help move molecules
Osmosis
✦ Passive transport
of water only
Direction of osmosis
✦ Hypotonic- water
moves into cell
✦ Water conc. is
high outside of cell
✦ Solute conc. is low
outside of cell
✦ Hypertonic- water
diffuses out of cell
✦ Water conc. is low
outside cell
✦ Solute conc. is
high outside of cell
7
✦ Isotonic- when
two environments
are equal, no net
movement
✦ “equilibrium”
Human Blood Cells
Cell Deal with Extra Water
✦ Animal- fills vacuole,
pump back out
✦ Some burst- cytolysis
(cell death)
✦ Plants- can swell,
pushing against cell
wall
✦ Called turgor pressure
Cells Deal with Limited
Water
✦ Animal cellsshrivel, eventually
die
✦ Plant- shrink
away from cell
wall
✦ Called plasmolysis
✦ Reason plants wilt
Active Transport
✦ Type of transport
in which
molecules
✦ Move from low to
high
concentrations
✦ Requires energy
✦ Types of Active
Transport
✦ Cell membrane
pumps
✦ Endocytosis
✦ Exocytosis
Cell Membrane Pump
✦ Uses protein
(pump) to force
molecules into
higher
concentration
Sodium-Potassium Pump
✦ Specific protein
that moves Na+
out and K+ into
the cell
✦ Carrier protein
can hold either 3
Na+ or 2 K+
Sodium-Potassium Pump
✦ 1. 3 Na+ enter protein, move to
outside
✦ 2. 2 K+ enter protein, move to inside
✦ 3. Cycle repeats
Endocytosis
✦ Process in which
large particles or
fluids are moved
into the cell
✦ Vesiclemembrane which
encloses the
particles and
moves them
around cell
Types of Endocytosis
✦ Pinocytosistransport of fluid
“cell drinking”
✦ Phagocytosistransport of large
particles or entire
cells “cell eating”
✦ Ex.- White Blood
Cells ingesting
bacteria
Exocytosis
✦ Process in which
large particles are
removed out of
the cell
✦ Starts in vesicle
then moves to cell
membrane
✦ Ex.- waste and
proteins are
removed