DIffusion question

[krje1980]

Hi.

I am planning on taking som college courses in Biology, and am currently reviewing High School biology in preparation for this.

In the section on prokaryote cells and bacteria I read the follwoing:

"Prokaryote organisms live in places where the concentration gradient is lower outside of the cell than within it. Thus, diffusion of water may cause the cell to swell. The cell membrane prevents the bacteria from swelling until it bursts."

OK, so I am a little bit confused here. I thought that water tends to move from areas of high concentration until areas of low concentration. So if the cell has higher concentration than its surroundings, shouldn't water diffuse out of the cell rather than into it? And if this happens, wouldn't the cell shrink instead of swell?

If anyone can explain the quoted paragraph to me I would greatly appreciate it!

[JackBean]

no, it's trying to make the concentrations the same, so the SOLUTE is going from high conc. to low, whereas water goes the other way.

[krje1980]

Thanks.

But why, exactly, would water move into the cell? I get that the overall solution has higher concentration inside the cell than outside it, but I still don't get why this would cause water to move into the cell unless the actual water concentration is higher outside of the cell than within it.

[JackBean]

think about it as - if there is more solute, there must be less water -> there's "gradient" of water as well. In reality, the change of water is pretty small, yet different.

[krje1980]

Yeah, it makes sense now. I read a bit further and it explained the whole diffusion topic in more detail. Thanks for your input though