Transcript Movement Across the Membrane

Movement Across the
Membrane
Chapter 6, Section 3
Diffusion
The net movement of molecules from areas of high
concentration to low concentration
Only the random motion of molecules is requiredNo Energy!!
In a fluid, molecules will diffuse until equilibrium (or
balance) is reached.
Passive Transport
Diffusion of substances across a selectively permeable
membrane
Carbon dioxide and oxygen freely diffuse across the
membrane
Water will also pass across the membrane, but often needs
the help of a protein
Facilitated Diffusion
A process in which a transport protein provides a
pathway or channel for molecules to pass across
the membrane
Osmosis
The diffusion of water across a selectively
permeable membrane
Osmosis and Osmotic Pressure
Hypotonic Solutions have
a LOW salt concentration
relative to the cell
Isotonic Solutions have a
salt concentration EQUAL
to the cell
Hypertonic Solutions have
a HIGH salt concentration
relative to the cell
How do cells deal osmotic pressure?
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Cell Wall- prevents plant cells from bursting
Contractile Vacuoles- pump out excess water
Bathe cells in isotonic/blood solutions
Kidneys/Gills remove excess water from blood
Active Transport
Movement against the concentration gradient that
REQUIRES ENERGY!!
Exs: protein pumps and transport of large molecules
Transport of Large Molecules
ENDOCYTOSIS
Takes material into
the cell within vesicles
EXOCYTOSIS
Vesicle fuses with
plasma membrane and
spills contents outside
the cell
A Summary: Side by Side