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Diffusion

Definition

noun

1. The passive movement of molecules or particles along a concentration gradient, or from regions of higher to regions of lower concentration.

2. The spontaneous net movement of particles down their concentration gradient (i.e. difference in the concentrations of substances or molecules between two areas).

3. (Cell biology): a type of passive transport, therefore, it is a net movement of molecules in and out of the cell across the cell membrane along a concentration gradient.


Supplement

Unlike active transport, diffusion does not involve chemical energy. When molecules move (diffuse) via special transport proteins found within the cell membrane, it is called facilitated diffusion, otherwise it is only simple diffusion. An example of diffusion in biological system is diffusion of oxygen and carbon dioxide across the alveolar-capillary membrane in mammalian lungs.

Word origin: From Latin diffusionem (accusative of diffusio), from verb diffundere.
Related forms: diffusional (adjective).
Compare: active transport, osmosis.
See also: passive transport.


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Re: diffusion

Bigger molecules diffuse more slowly.

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by jonmoulton
Fri Apr 04, 2014 2:59 pm
 
Forum: Cell Biology
Topic: diffusion
Replies: 2
Views: 692

diffusion

how does the size of a molecule affect the rate of diffusion. I am confused how this works. any help would be appreciated.

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by kristenb
Fri Apr 04, 2014 6:12 am
 
Forum: Cell Biology
Topic: diffusion
Replies: 2
Views: 692

Re: Diffusion and concentration gradient

1) the answer of Arlen1991 is completely irrelevant to your question! 2) Darby's analogy is perfect 3) it's simply about entropy . The molecules move randomly in any direction without any knowledge of presence of other molecules (alike or different). So just by following probability they spread rand...

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by JackBean
Thu Dec 26, 2013 5:49 pm
 
Forum: General Discussion
Topic: Diffusion and concentration gradient
Replies: 7
Views: 4722

Re: Diffusion and concentration gradient

... from B to A. After all, O2 can't diffuse out of region B if it isn't already present in region B. If B is filled with mostly CO2, then most of the diffusion out of B will be of CO2.

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by wildfunguy
Thu Dec 19, 2013 12:51 am
 
Forum: General Discussion
Topic: Diffusion and concentration gradient
Replies: 7
Views: 4722

Diffusion and concentration gradient

... from CO2 and NOT O2? Conversely, how do the CO2 molecules realise that the air in the alveoli is O2-rich but low in CO2... At first I thought that diffusion depended on 'space', whereby any molecule tries to get as much space around itself as possible and hence moves towards lower concentrations. ...

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by Aymeric
Sun Dec 15, 2013 1:02 am
 
Forum: General Discussion
Topic: Diffusion and concentration gradient
Replies: 7
Views: 4722
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