4.2- Diffusion

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  • Created by: Megan2413
  • Created on: 12-12-16 11:34
What is the definition of diffusion?
It is the net movement of particles from an area of high concentration to lower concentration
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What does 'net' mean in respect to diffusion?
That molecules will diffuse in both directions but the overall (net) movement is down the concentration gradient
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Why is diffusion a passive process?
It doesn't use energy
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What is the definition of simple diffusion?
When molecules diffuse directly through a cell membrane
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What makes molecules able to pass through a membrane by simple diffusion?
- Small enough to pass through the space between phospholipids - Non-polar molecules as this makes them soluble in lipids so they can dissolve in the hydrophobic bilayer
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What proteins does facillitated diffusion use?
Channel and carrier proteins
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Why do large molecules diffuse by facillitated diffusion?
As they are large they would diffuse extremely slowly through the bilayer
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Why do charged particles (such as polar molecules and ions) diffuse by facillitated diffusion?
As they are charged, this makes them water soluble, and the centre of the phospholipid bilayer is hydrophobic
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What is the definition of facilliatetd diffusion?
When molecules use channel and carrier proteins to diffuse through a cell membrane
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Does facilliatetd diffusion move molecules down their concentration gradient?
Yes
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Is facilliatetd diffusion a passive or active process?
Passive
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What do carrier proteins do?
They move molecules or ions down their concentration gradient
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Will one carrier protein facillitate the diffusion of several different molecules?
No- they have specific binding sites
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Explain in a few steps how carrier proteins carry out facillitated diffusion?
- A molecule/ion attaches itself to the binding site of the carrier protein in the membrane from an area of high concentration - The protein changes shape - The molecule's released on the other side of the membrane to an area of low concentration
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How do channel proteins work?
They form water filled channels in which water soluble substances can travel down
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Which three factors affect the rate of simple diffusion
- Concentration gradient - Thickness of exchange surface - Surface area
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Explain how each factor affects the rate of diffusion
- The higher the concentration gradient the faster the rate of diffusion; as diffusion takes place the difference in concentration on each side of the membrane decreases until it reaches an equilibrium: diffusion slows down over time - The thinner
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--> continuation
the exchange surface, the shorter distance for molecules to travel hence the faster the rate of diffusion - The larger the surface area, the more space there is for diffusion hence the faster the rate of diffusion
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Why can water also diffuse by simple diffusion as well as facilliated diffusion even though its a polar molecule?
It is relatively small
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Card 2

Front

What does 'net' mean in respect to diffusion?

Back

That molecules will diffuse in both directions but the overall (net) movement is down the concentration gradient

Card 3

Front

Why is diffusion a passive process?

Back

Preview of the front of card 3

Card 4

Front

What is the definition of simple diffusion?

Back

Preview of the front of card 4

Card 5

Front

What makes molecules able to pass through a membrane by simple diffusion?

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