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CELL TRANSPORT
Chapter 8
Passive Transport
• Many substances move in & out of the
cell using NO ENERGY
• This is called Passive Transport
• 2 Types:
• 1) Simple Diffusion: Move from high
conc → low conc
• 2) Facilitated Diffusion
Facilitated Diffusion
• Many molecules are too large to diffuse
through lipid bilayer
• Instead, they use carrier proteins, which
can change shape, to get across
• Facilitated Diffusion: diffusion across a
cell membrane with help of carrier proteins
• Is passive (no energy)
• Facilitated Diffusion
Active Transport
• At times, molecules may have to move
against the concentration gradient
• Low conc. → High conc.
• This REQUIRES ENERGY, and is called
Active Transport
• 3 Types:
• 1) Sodium/Potassium Pumps
• 2) Endocytosis
• 3) Exocytosis
Sodium/Potassium Pump
• Transports sodium (Na+) and potassium
(K+) against their concentration gradients
• Animals need more Na+ outside/more K+ inside
• Pump must change shape to fit Na+/K+
• Energy for this comes from ATP in mitochondria
• Each cycle = 3 Na+ out and 2 K+ in
Endocytosis
• Involves folding cell
membrane around
LARGE molecules to
bring into cell in
vesicle
• Vesicle: membrane-
bound organelle
containing food & other
molecules
Endocytosis (con’t)
2 types:
Pinocytosis: intake of fluids
Phagocytosis: intake of solids
Exocytosis
• Reverse of endocytosis
• Vesicle fuses with cell membrane to
release LARGE molecules from cell
How Cells Deal with Osmosis
• Human cells usually exist in isotonic
solutions
• Many cells exist in hypotonic solutions
• i.e.: paramecia, plants
• Water constantly diffuses in
• Organisms must get rid of excess H2O
• Contractile Vacuole: organelle in paramecia
used to pump H2O out
• Cell walls keep plant cells from bursting
Active and Passive Cell Transport
• Cell Transport