Osmosis

[kaylabarber]

This is basically a true or false statement. If it is false, I am supposed to rewrite a correct statement:

 

Osmosis will not take place if a dead cell is placed in a solution hyotonic to its contents.

 

I am aware of what osmosis is and I also know that a cell in hypotonic solution will expand due to the lower solute concentration outside of the cell. However, I am not aware if dead cells are able to go through osmosis nor can I find information regarding dead cells and osmosis anywhere.

 

Thanks for any help

[hermanntrude]

bear in mind that osmosis also happens in man-made systems and in completely non-living environments. It is a passive process (nothing has to be actively done to make it happen), and it comes from the random diffusion of atoms, ions and molecules across the membrane

[kaylabarber]

Excellent. Thank you.

[CharonY]

Actually, it depends. Cells can rapidly lose membrane integrity and selectivity. Thus ions would eventually be able to move through the membrane unhindered thus preventing osmosis.

[hermanntrude]

a single dead cell wouldnt decompose as fast as a dead cell in a dead body

[CharonY]

It is not a matter of decomposition. But rather that proteins in the membrane lose their selectivity. The first thing that happens when a cell dies is that that proton gradient is lost. Small and even charged molecules start diffusing through pores and channels.

Also, a dead cell is a dead cell. What does the body has to do with it?

The important bit is that a cell does not has a completely closed lipid membrane. If it was, it would work simply as a semi-permeable membrane for charged molecule. However, cells are riddled with porins, channels, etc. which allow the passage of molecules. The selectivity of the membrane then, however, is often dependent on cellular activity.

[hermanntrude]

in other words, cells interfere with osmosis?

[CharonY]

Not necessarily (depending on precisely what you mean with interfere, I may be misunderstanding you). But the selectivity for specific ions or any other compounds of a cell depends to a large part on cell activity. Once a cell dies it becomes porous and diffusion rather than osmosis occurs.

Just to summarize: osmosis is a passive process, but it requires a semi-permeable membrane. The membrane of most cells is essentially porous, it possesses numerous channels, porins etc. that are large enough to let ions through the (hydrophobic) membrane. However, while the cell lives it also exhibits a selectivity of the ions to maintain certain gradients, for instance or a certain homeostasis for specific ions. Under this condition osmosis can occur. Once a cell dies, however the active processes cease and will be superseded by diffusion.

 

Edit: If you meant whether cells control osmosis, then yes, depending on cell type and up to a certain limit.

Edited May 21, 2009 by CharonY