Passive transport, such as diffusion and osmosis, moves materials of small molecular weight across membranes.
The hydrophobic and hydrophilic regions of plasma membranes aid the diffusion of some molecules and hinder the diffusion of others.
Diffusion is a process of passive transport in which molecules move from an area of higher concentration to one of lower concentration.
Facilitated diffusion is a process by which molecules are transported across the plasma membrane with the help of membrane proteins.
Osmosis is the movement of water across a membrane from an area of low solute concentration to an area of high solute concentration.
Tonicity, which is directly related to the osmolarity of a solution, affects osmosis by determining the direction of water flow.
Osmoregulation is the process by which living things regulate the effects of osmosis in order to protect cellular integrity.