Diffusion
the movement of molecules form an area of high concentration of molecules to an area of lower concentration of molecules
Permeability
when the membrane allows a substance to pass through it
Facilitated diffusion
protein-mediated transport in which no outside source of energy is needed to move molecules across the cell membrane
Active transport
requires the input of energy from some outside source and moves against the concentration gradient
Osmosis
the movement of water across a membrane in response to solute concentration gradient
Osmolarity
the number of osmotically active particles per liter of solution
Tonicity
a physiological term used to describe a solution and how the solution would affect cell volume if the cell were placed in the solution and allowed to come to equilibrium
Endocytosis
active process that requires energy from ATP, it can be nonselective, allowing extracellular fluid to enter the cell, or it can be highly selective only allowing specific molecules into the cell.
Exocytosis
the opposite of endocytosis; intracellular vesicles move to the cell membrane, fuse with it, and then release their contents to the extracellular fluid.
Epithelial transport
molecules entering and leaving the body or moving between certain compartments within the body must cross a layer of epithelial cells that are connected to one another by adhesive junctions and tight junctions
Water channels
channel made from a protein called aquaporin
Ion channels
may be specific for one ion or may allow ions of similar size and charge to pass
Open channels
spend most of their time with their gate open, allowing ions to move back and forth across the membrane without regulation.
Gated channels
spend most of their time in a closed state, which allows these channels to regulate the movement of ions through them
transcytosis
a type of transcellular transport in which various macromolecules are transported across the interior of a cell