Facilitated diffusion can be limited by the number of proteins available and present and hence, after a certain point, the rate will not increase despite change in aforementioned factors
diffusion of water molecules from a region of lower solute concentration to higher solute concentration
across a partially permeable membrane
Osmotic potential: tendency of water to move into a solution - greater solute concentration, greater the osmotic potential
occurs due to small size of water molecules that can pass through membrane
Recall that the main function of the plasma membrane is transport. Generally, transport is defined as passive or active.
Active transport, like (passive) facilitated diffusion requires proteins. However, these proteins use energy in form of ATP to pump molecules against their concentration gradient. There are two types of active transport: Primary: direct use of metabolic energy for transport of molecules against concentration gradient. Secondary: coupling the movement of one molecule against the concentration gradient with the movement of another along the concentration gradient of the second molecule, often created by primary active transport.
Exocytosis: Transport of molecules in secretory vesicles that fuse with the plasma membrane upon contact to release the contents outside of the cell
Endocytosis transport of molecules into the cell through invagination of the plasma membrane and formation of the phospholipid vesicle containing the molecule.