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Is osmosis diffusion of water?

Biology Asked by mpnm on December 14, 2021

My textbook says this:

Osmosis is the diffusion of water.

Wikipedia says this:

The diffusion model of osmosis is rendered untenable by the fact that osmosis can drive water across a membrane toward a higher concentration of water.

It’s my understanding that diffusion is passive transport, and it moves material from a highly concentrated area of that material to an area where it is in lower concentration. By this definition, it looks like Wikipedia is correct. But if for example, a cell is put in saltwater, water from within the cell would go out. Is this diffusion now? Which definition is correct?

I would just go with the Wikipedia definition because it actively describes its own definition as a refinement of the textbook definition, but the paragraph above in the article is a bit confusing to me.

2 Answers

Yes, In most cases, osmosis is the diffusion of water. To my understanding, what I think Wikipedia is trying to do is to assert the fact that osmosis is also be the movement of water from a region of lower water potential to a region of higher water potential. These kinds of contradictions, as much as scientists try to avoid them, still come to play because science is very complicated. Just when we start accepting a theory, it gets discarded by another theory.

Answered by Taofeek on December 14, 2021

Osmosis is about solutions (solvent + solute).

Osmosis is a movement of the solvent through certain types of membranes. These membranes let the solvent move across them, but not the solute. The process tends to balance the solute concentration on both sides of the membranes.

If we say that the solvent is water and the solute is salt (NaCl). Water will move from the side of the membrane where the salt concentration is low toward the side where the salt concentration is high. At the end of the process both concentrations will be equal.

In biology it is a very important process at a cellular level (cell membranes are semi-permeable membranes) but also plays a key role in food digestion or kidney reabsorption, for instance. Cells (bacteria) that are put in solutions with high concentration of salt die of loosing the water they contain.

Answered by JeanV on December 14, 2021

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