In cellular biology, an<unk>  refers to the electrical and chemical properties across a membrane. These are often due to ion gradients, particularly proton gradients, and can represent a type of potential energy available for work in a cell. This can be calculated as a thermodynamic measure termed<unk>  potential that combines the concepts of energy stored in the form of chemical potential which accounts for an ion's concentration gradient across a cellular membrane and electrostatics which accounts for an ion's tendency to move relative to the membrane potential.<unk>  potential is important in electroanalytical chemistry and industrial applications such as batteries and fuel cells. It represents one of the many interchangeable forms of potential energy through which energy may be conserved.
In biological processes the direction an ion will move by diffusion or active transport across membrane is determined by the<unk> . In mitochondria and chloroplasts, proton gradients are used to generate a chemiosmotic potential that is also known as a proton motive force. This potential energy is used for the synthesis of ATP by oxidative phosphorylation.
An<unk>  has two components.  First, the electrical component is caused by a charge difference across the lipid membrane. Second, a chemical component is caused by a differential concentration of ions across the membrane. The combination of these two factors determines the thermodynamically favourable direction for an ion's movement across a membrane.<unk> s are analogous to hydroelectric dams and equivalent to the water pressure across the dam. Membrane transport proteins such as the sodium-potassium pump within the membrane are equivalent to turbines that convert the waters potential energy to other forms of physical or chemical energy, and the ions that pass through the membrane are equivalent to water that is now found at the bottom of the dam.  Alternatively, energy can be used to pump water up into the lake above the dam.  Similarly chemical energy in cells can be used to create<unk> s.
Electrochemical gradient
Pressure gradient 
Gas constant
Membrane potential
Volumetric flow rate
Molecular mass
Anion gap
Oxygen permeability