cell and surrounding membrane

process by which substances move across a selectively permeable membrane such as a cell's plasma membrane

movement of molecules from an area of relatively high concentration to an area of relatively low concentration

requires an input of energy in the form of ATP, can be used to move ions and molecules across the plasma membrane and is often used to move them from areas of low concentration to areas of high concentration

concentration of dissolved substances

osmolarity inside the cell must equal osmolarity outside the cell

determined by molecules that cannot cross the cell boundary

The molar concentration of a solution, usually expressed as the number of moles of solute per liter of solution