This does not require a supply of energy because diffusion is a spontaneous process. This occurs when molecules are moved across the cell membrane from an area where they are at a low ...

Cell membranes protect and organize cells. All cells have an outer plasma membrane that regulates not ... which means that some molecules can diffuse across the lipid bilayer but others cannot.

Diffusion Substances move from a high ... eg urea No Osmosis Water moves from a high to a lower concentration across a partially permeable membrane and down a concentration gradient Water No ...

Together, these concentration differences create a small electrical potential across the plasma membrane ... process of molecular diffusion. As a consequence, excitable cells respond to signals ...