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Diffusion

Cell membrane
Lipid bilayer

Cell membrane
Carbohydrate
chains
Proteins
Protein
channel
Cell membrane


Every living cell exists in a liquid
environment.
The cell membrane regulates movement of
molecules from the liquid on one side of the
membrane to the liquid on the other side.
Cell membrane


Important part of the cell because they help
the cell maintain homeostasis
Homeostasis = a state of equilibrium
Solutions
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Solutes dissolve in solvents
Solute examples:
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Oxygen, carbon dioxide, salt, sugar, amino acids
Water is the universal solvent
Diffusion
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Particles in a solution tend to move from an area of
HIGH concentration to an area of LOW
concentration.
HIGH
Equilibrium
LOW

When the concentration of the solute is the same
throughout a system, the system has reached
equilibrium.
Diffusion

NO energy is required from the cell in order
for diffusion to occur
Osmosis

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Diffusion of water through a semi-permeable
membrane.
Semi-permeable - allows water to pass through,
but not large molecules
Osmosis
Isotonic –
concentrations
same inside and
outside
Hypertonic – water
leaves the cell b/c higher
concentration of water is
inside of the cell
Hypotonic – water
enters the cell b/c higher
concentration of water is
outside of the cell
Osmosis

“Hold your wee for a Wii” 2007 radio contest

Contestant died from consuming too much water,
caused her cells to become hypotonic (filled with
water), and eventually burst.
Why does salt kill slugs?
Facilitated Diffusion
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Cell membranes have protein
channels that act as carriers, making
it easy for certain molecules to cross.
Involves the movement of molecules
across cell membranes through
protein channels
Facilitated Diffusion
Facilitated Diffusion

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Facilitated diffusion will only occur if there is a
HIGHER concentration of the particular
molecules on one side of a cell membrane as
compared to the other side.
Since facilitated diffusion is still diffusion, it
does NOT require energy in order to occur
Active Transport


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Sometimes cells move materials in the
opposite direction from which the
materials would normally move—that is
against a concentration difference.
Active transport requires energy.
Small molecules and ions are carried
across membranes by proteins in the
membrane.
Active Transport
Molecule to be carried
Endocytosis

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Process of taking material INTO the cell by
means of infoldings, or pockets, of the cell
membrane.
The pocket breaks loose from the cell
membrane and forms a vacuole within the
cytoplasm.
Two examples:
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Phagocytosis
Pinocytosis
Endocytosis
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Phagocytosis
Extensions of
cytoplasm surround a
particle and then
engulfs it

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Pinocytosis
Tiny pockets form along
the cell membrane, fill
with liquid, and pinch
off
Exocytosis

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Some cells release large
amounts of material from the
cell
The membrane of the
vacuole surrounding the
material fuses with the cell
membrane, forcing the
contents OUT of the cell
Cell Volume vs Surface Area

In cells:

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Volume – amount of space that can be filled with
cytoplasm, organelles and other molecules
Surface area – amount of cell membrane
available for the transport of molecules in or out of
the cell
The greater the surface area, the larger the
amount of molecules that can enter or exit a cell
at one time.
Cell Volume vs Surface Area
The
greater the surface area, the larger the amount of
molecules that can enter or exit a cell at one time.

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Slightly more volume
Less surface area

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Slightly less volume
More surface area
Your body is made up of millions of cells because more cells =
more surface area. More surface area = more efficient system