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Movements
Movements Through
Through
Cell
Cell Membranes
Membranes
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Selective Permeability
 The plasma membrane allows some materials
to pass while excluding others
 This permeability includes movement into
and out of the cell
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Cellular Physiology: Membrane Transport
 Membrane Transport – movement of
substances into and out of the cell
 Transport is by two basic methods
 Passive transport
 No energy is required
 Active transport
 The cell must provide metabolic energy
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Movement Through Cell Membrane
 Passive Mechanisms of transport require
no cellular energy
 Ex:
 Simple Diffusion
 Facilitated Diffusion
 Osmosis
 Filtration
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Passive Transport Processes
 Diffusion
 Molecules move
from high
concentration
to low
concentration,
or down a
concentration
gradient
 Equilibrium- Molecules tend to distribute
themselves evenly within a solution
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DIFFUSION ANIMATION
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Figure 3.9
Diffusion through the Plasma Membrane
Figure 3.10
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Passive Transport Processes
 Facilitated diffusion
 Substances require a protein carrier (or
Carrier Molecule) for passive transport
 The rate of facilitated diffusion is limited to
the number of carrier molecules in the
membrane and/or the number of molecules
available for transport.
 Insulin promotes facilitated diffusion of
glucose
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Facilitated Diffusion
• diffusion across a membrane with the help of a channel
or carrier molecule
• glucose and
amino acids
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Passive Transport Processes
 Osmosis –
 simple diffusion of water from area of higher
concentration to lower concentration
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Osmosis
• movement of water through a selectively permeable membrane
from region of higher concentration to region of lower concentration
• water moves toward a higher concentration of solutes
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Passive Transport
 These are red blood cells in three
different solutions:
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Passive Transport
 Hypertonic Solution
 Has more solute
particles (thus less
H2O) than a cell in
that solution
 Result: Plasmolysiscell shrinks
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Passive Transport
 Hypotonic Solution
 Has less solute particles
(thus more H2O) than a
cell in that solution
 Result: Cytolysis- cell
bursts
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Passive Transport
 Isotonic Solution
 Has the same
concentration of
solute particles as a
cell in that solution
 Result: Cell remains
unchanged
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Passive Transport
 Can you identify the solution each cell
is in and explain what happens to each
cell?
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Active Transport Processes
 Active Mechanisms require
cellular energy (ATP)
 Active Transport Particles move from
an area of lower
concentration to
higher concentration
 Up to 40% of cell’s
energy supply is used
for active transport
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Active Transport Processes
 Solute pumping
 Amino acids, some sugars and ions are
transported by solute pumps
 ATP energizes protein carriers, and in
most cases, moves substances against
concentration gradients
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ACTIVE TRANSPORT ANIMATION
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Active Transport Processes
Figure 3.11
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Active Transport Processes
 Bulk transport
 Endocytosis
 A portion of the cell membrane forms
vesicle to carry in particles too large for
diffusion or pumping
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Endocytosis
Figure 3.13a
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Active Transport Processes
 Types of endocytosis
 Pinocytosis – cell drinking:
 Portion of cell membrane becomes
indented and surrounds tiny droplets of
liquid. Membrane pinches off and carries
liquid into cytoplasm where it releases
contents
 Phagocytosis – cell eating:
 Solids are engulfed by indented portion of
cell membrane which then pinches off and
acts as vesicle to carry & empty solids into
cytoplasm
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Active Transport Processes
 Bulk transport
 Exocytosis
 Moves materials out of the cell
 Material is carried in a membranous vesicle
 Vesicle migrates to plasma membrane
 Vesicle combines with plasma membrane
 Material is released to the outside
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Exocytosis
Figure 3.12a
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