Cell Transport
The movement of molecules can be either
passive (no energy) or active (needs energy)
depending upon the membrane structure
and concentration gradients.
Transport through cell
membranes
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Transport through cell membranes
•
The cell membrane is a good barrier around cells, especially to
water soluble molecules. However, for the cell to survive some
materials need to be able to enter and leave the cell.
There are 3 basic mechanisms:
1.
DIFFUSION
2.
OSMOSIS
3.
ACTIVE TRANSPORT
•
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Diffusion of liquids
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•Diffusion is the net movement of molecules (or
ions) from a region of their high concentration to
a region of their lower concentration.
The molecules move down a concentration gradient.
Molecules have kinetic energy, which makes them move
about randomly.
As a result of diffusion molecules reach an equilibrium
where they are evenly spread out.
This is when there is no net movement of molecules from
either side.
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DIFFUSION
Diffusion is a PASSIVE process which means no energy is used
to make the molecules move.
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Diffusion through a membrane
Observe the molecules moving from a region of
Cell membrane
high to low.
Inside cell
Outside cell
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Diffusion through a membrane
Cell membrane
diffusion
Inside cell
Outside cell
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Diffusion through a membrane
Cell membrane
Outside cell
Inside cell
EQUILIBRIUM
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Molecules that diffuse through cell
membranes
1.
Oxygen – so diffuses
very quickly.
1.
Carbon dioxide –
very small so
diffuses quickly.
2.
Water – very small
so diffuses quickly.
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Osmosis
‘The diffusion of water from an area
of high concentration of water
molecules to an area of low
concentration of water across a
semi permeable membrane.’
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Osmosis
DILUTE SOLUTION
Sugar molecule
CONCENTRATED SOLUTION
Cell membrane
partially
permeable.
VERY Low conc. of
water molecules.
High water potential.
VERY High conc. of
Inside cell
water molecules.
High water potential.
Outside cell
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Osmosis
Cell membrane
partially
permeable.
Low conc. of water
molecules. High
water potential.
OSMOSIS
High conc. of water
molecules. High
water potential.
Inside cell
Outside cell
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Osmosis
Cell membrane
partially
permeable.
OSMOSIS
Inside cell
Outside cell
EQUILIBRIUM. Equal water concentration on each side. Equal water
potential has been reached. There is no net movement of water
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Red Blood Cell Placed in both salt
water and distilled water.
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Look what happens to plant cells in
both salt water and distilled water!
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Receptor Proteins
These proteins are used in intercellular communication. In this animation you can see
the a hormone binding to the receptor. This causes the receptor protein release a
signal to perform some action.
• Found on surface
• Detects hormones
• Acts as binding site
on Cell Membrane
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