How do water molecules move through the cell membrane during osmosis?

2 Answers
Sep 2, 2015

The water molecules move across the cell membrane by travelling along the concentration gradient of the solution (low to high).


  • Osmosis is the process in which a solvent moves from a solution of low concentration to a solution of higher concentration .
  • A gradient is followed for this movement and once the concentration of both the solutions(on either sides of the membrane) becomes equal the solvents stop flowing.

Now consider two solutions A and B.
A - is dilute
B - is concentrated
They are both separated by a cell membrane.

Water(solvent) molecules travel from A across the cell membrane / semi permeable membrane to B until the concentrations of A and B become equal.

Water can move through the cell membrane directly through the membrane (simple diffusion ) or through protein channels called aquaporins.


Small molecules such as water and carbon dioxide can pass directly through the membrane because of they are neutral and so small. The movement of water through the membrane is referred to as osmosis.

The movement of water through the plasma membrane depends on the construction of the membrane. For example, a membrane which has a lot of cholesterol incorporated in the membrane will not allow water to pass as easily through it. A membrane with less cholesterol will have a greater permeability for water.

Water can also pass through the membrane through channel proteins called aquaporins (AQP).

Here is a video which discusses the process of facilitated diffusion.

And this video discusses the impact of osmosis on red onion cells when placed into hypertonic and hypotonic solutions.

This video show microscope images of red onion cells placed into a hypertonic environment.

Hope this helps!