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CELL TRANSPORT
How substances get across the
membrane…
Diffusion Across Cell Membrane
Semi-permeable membrane
 Allows only certain molecules
across
 H2O
 CO2 and O2
Passive Transport
Movement of substances
across the cell membrane
Requires no energy from
the cell
Diffusion is the simplest
type of passive transport
DIFFUSION
Movement of molecules from HIGH
concentration to LOW concentration
Concentration Gradient - the
difference between concentrations in
space
Simple diffusion only allows certain
molecules across a membrane
Eventually it will hit an
equilibrium
(same concentration across
the gradient)
OSMOSIS
A type of diffusion
Process by which WATER
molecules diffuse across a
membrane from high to low
concentrations
10% Salt Solution
• % solutions have to equal 100
• 10% salt (solute) would leave how
much water (solvent)?
• 90% water
• Hyper = above
• Iso = same
• Hypo = below
tonic refers to the
shape of the cell
How Cells Deal With Osmosis
Animal Cells:
Contractile
Vacuoles
 Collects
water and
expels it from
the cell
How Cells Deal With Osmosis
Plants:
Turgor Pressure
 Water pressure
that is exerted
against cell
wall
Plasmolysis – loss of turgor pressure
 Plants wilt
Cytolysis – cells burst due to
hypotonic solution cell is in
Facilitated Diffusion
-needs a carrier protein
Ion Channels
• Transport ions such as Na, K, Ca and
Cl
• Can’t pass through membrane w/o
channel
Active Transport
Moving molecules from a LOW
concentration to a higher
concentration
Moving “up” their concentration
gradient
Requires energy from in cell

ATP
Active Transport
Need a pump
SodiumPotassium
Pump
Exchanges
Na and K
 Na to the
outside
 K to the
inside
Other Transport Mechanisms
Endocytosis – process of ingesting
macromolecules and nutrients that
are too large to pass through
membrane
Two types:
Pinocytosis
Transport of other fluids
Phagocytosis
Transport of large particles or whole
cells
Phagocytes may fuse with lysosomes
to destroy ingested bacteria or
viruses
Other Transport Mechanisms
Exocytosis – process by which
materials are released from the inside
of the cell
Release toxins and waste products
Release proteins

Control activity of other cells