Passive Transport Vs Diffusion

[gempaq]

Is it safe to say that Passive Transport and Diffusion two wholly different processes?

[fredrik]

Diffusion is a kind of passive transport. So the term "passive transport" is normally meant wider than just "diffusion". The meaning of passive is that the transport does not require active energy supply, and the transport is driven by the natural thermodynamical (downhill) gradient of the transported compound itself. In biology so called facilitated diffusion is common, and it usually means that the cell membrane contains transport channels (that doesn't require energy - ie NOT pumps) that simply stimulates diffusion by their presence. The degree of facilitation can be regulated, but there is no power supply involved.

 

The opposite - active transport, require an energy supply of some sort and can thus transport stuff against the natural thermodynamic gradient (uphill).

 

/Fredrik

[gempaq]

So are diffusion and passive transport the same?

[fredrik]

Maybe depends on the context but I'd say is not exactly the same though a bit close. Plain diffusion is a kind of passive transport.

 

But in biology contexts one usually makes distinctions between different types of passive transport: osmosis, facilitated diffusion and more "straight/simple diffusion". Even though they are related from a very basic point of view, the differences between the transport types are important when talking about cells.

 

The classifications based on *energy requirement* are passive vs active transport.

 

Then there are different types of passive transport, the same way there are different types of active transport, this fruther classification is based on transport mechanism.

 

Osmosis, plain diffusion and facilitated diffusion are all in a sense "diffusion". But to a cell there is quite a difference between them. Plain diffusion through a cell membrane means the diffusing spieces go right through the membrane, and regulations mean regulating the membrane. Facilitated diffusion means the cell has synthesised special typically membrane proteins acting as tunnels for diffusions, and regulation menas just regulating these transport proteins. These tunnels can be powered like pumps (active transport) or non-powered (facilitated diffusion).

 

/Fredrik

[gempaq]

Thanks a bunch!

[blike]

In my experience, passive transport indicates that proteins are involved but no energy is expended (i.e. voltage gated Na-channels in axons), whereas passive diffusion means the substance can simply passively diffuse across the membrane (i.e. small hydrophobic molecules).

[Genecks]

Someone once told me quantum energy is still involved, but I'm not too sure about it all.