# Does osmosis happen through the phospholipids or through proteins?

Both!

#### Explanation:

Osmosis is the diffusion of water into or out of cells depending on the concentration gradient. Water will flow from where the water is at a higher concentration to where water is at a lower concentration.

Watch this video for a discussion of changes in red onion cells placed into pure water or salt water environments.

Small, nonpolar molecules that can diffuse through the cell membrane include ${O}_{2} \mathmr{and} C {O}_{2}$. Larger molecules (glucose for example) are too large to do this. Water molecules are small enough to move through the phospholipid bilayer, but their polarity means they do not move as easily as ${O}_{2} \mathmr{and} C {O}_{2}$ through the membrane.

So how else can water move into or out of cells?

Water can also move into or out of cells through channel proteins called aquaporins . These proteins molecules act as doorways through which water can pass.