L.O: to define diffusion and facilitated diffusion

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Diffusion

• L.O to define diffusion and facilitated
  diffusion
• to state factors affecting diffusion
• Starter Recap on Osmosis
• a) What would happen to a red blood cell placed
  in a solution with low water potential
  (hypotonic)?
• b) What would happen to a plant cell placed in a
  solution with lower water potential (hypotonic)?

2
Diffusion

• L.O to define diffusion and facilitated
  diffusion
• to state factors affecting diffusion

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Transport across the cell membrane
All cells are surrounded by a partially-permeable
membrane that controls what substances can enter
and exit the cell.
A cell needs to be able to import the substances
it needs to survive, and to export waste
materials and substances that are needed outside
the cell.
There are several methods by which substances
(molecules and ions) can cross the cell membrane

• diffusion

• osmosis

• active transport.

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Diffusion

• The movement of molecules or ions from a region
  of high concentration to a region of low
  concentration.
• It is a passive process, so requires no ATP
  (energy).

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• http//mrhardy.wikispaces.com/Diffusion.swf 

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Facilitated Diffusion?

• What on earth is it?
• Discuss in pairs

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Facilitated Diffusion

• Diffusion involving the presence of protein
  carrier molecules to allow the passive movement
  of substances across a plasma membrane.

8
http//highered.mcgraw-hill.com/sites/0072495855/s
tudent_view0/chapter2/animation__how_facilitated_d
iffusion_works.html
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L.O.2 Factors Affecting Diffusion

• There are 4 factors affecting diffusion
• You investigated one factor during the induction
  lesson back in July.!
• You have just seen another factor during the demo
• Think and discuss what the other two factors
  could be

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Ficks Law
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Movement Across the Membrane
Diffusion Facilitated Diffusion Osmosis Active Transport
Direction along conc. gradient
ATP (energy) needed?
Carrier / channel proteins used?
What is moved?
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Movement Across the Membrane
Diffusion Facilitated Diffusion Osmosis Active Transport
Direction along conc. gradient Down Down Down
ATP (energy) needed? No No No
Carrier / channel proteins used? No Yes No
What is moved? Molecules Molecules Water