Transcript 253614_osmosis_diffusion.ppt

Biology Chapter 7.3
Movement of materials through
cell membranes
Passive Diffusion
Passive- no energy is required by the cell for movement
Osmosis-Diffusion of WATER across cell
membranes from high concentration to low
concentration (also passive transport)
Concentration gradient
Net movement is DOWN the gradient, from areas of high
concentration to areas of low concentration
Passive diffusion of solute into a cell is linearly related
to the concentration of solute outside the cell
States of equilibrium
•
•
•
• Hypotonic- concentration of solute molecules is lower outside the cell
than the cytosol (inside cell)
Water diffuses into the cell (cell expands)
• Hypertonic- concentration of solute molecules is higher outside the
cell than the cytosol
Water diffuses out of the cell (cell shrinks)
• Isotonic- concentration of solute molecules is equal between the
inside and outside of cell
Water diffuses in and out of the cell at equal rates
How do cells deal with osmosis?
Contrtactile vacuoles pump water out
Normal isotonic Elodea
Elodea with Plasmolysis
Hypertonic Solution
*Facilitated Diffusion- movement of molecules happens with the
assistance of carrier proteins
Usually because these molecules are too large to diffuse through the
membrane, the molecule is impermeable to the membrane, and even in
thepresence of a concentration gradient
Passive transport because molecules moving from high concentration to
low concentration
Carrier proteins increase the rate of diffusion by allowing more
solute to enter the cell. Facilitated diffusion, however, approaches a
maximum rate as the carrier proteins become saturated with solute.
*Active Transport-movement of molecules against the
concentration gradient (from low to high concentration)
Energy is required for this process to occur
Sodium Potassium pump
endocytosis
• A process where cells
INGEST external
fluid. Macromolecules
and large particles.
• Enclosed in a pouch
called a vesicle to
attach to & be digested
by vesicles
phagocytosis
• A type of endocytosis.
• Whole cells are
engulfed.
• (amoeba engulfing a
bacterium)
Pinocytosis
• A form of endocytosis
• Pockets of nutrients
pinch off (vesicles)
and are released from
the cell to the
environment or other
parts of the cell.
• Membrane from the
cell becomes vesicle
membrane
3 forms of endocytosis
Exocytosis
• Opposite of endocytosis
• Membrane bound vesicles
of substances fuse to the
cell membrane which
breaks down releasing
contents to the external
environment.
• Large molecules and
pieces of cells are
released.
Animal cell