1. Cell Transport
The movement of molecules can be either passive (no energy) or active (needs energy) depending upon the membrane structure and concentration gradients.

2. Transport through cell membranes
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3. 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:
DIFFUSION
OSMOSIS
ACTIVE TRANSPORT
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4. AS Biology, Cell membranes and Transport
Diffusion of liquids
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5. AS Biology, Cell membranes and Transport
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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6. AS Biology, Cell membranes and Transport
DIFFUSION
Diffusion is a PASSIVE process which means no energy is used to make the molecules move.
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7. Diffusion through a membrane
Observe the molecules moving from a region of high to low.
Cell membrane
Outside cell
Inside cell
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8. Diffusion through a membrane
Cell membrane
diffusion
Outside cell
Inside cell
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9. Diffusion through a membrane
Cell membrane
Outside cell
Inside cell
EQUILIBRIUM
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12. Molecules that diffuse through cell membranes
Oxygen – so diffuses very quickly.
Carbon dioxide – very small so diffuses quickly.
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
CONCENTRATED SOLUTION
DILUTE SOLUTION
Cell membrane partially permeable.
Sugar molecule
VERY Low conc. of water molecules. High water potential.
VERY High conc. of water molecules. High water potential.
Outside cell
Inside cell
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15. AS Biology, Cell membranes and Transport
Osmosis
Cell membrane partially permeable.
Low conc. of water molecules. High water potential.
OSMOSIS
High conc. of water molecules. High water potential.
Outside cell
Inside cell
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16. AS Biology, Cell membranes and Transport
Osmosis
Cell membrane partially permeable.
OSMOSIS
Outside cell
Inside 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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17. 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
AS Biology, Cell membranes and Transport