To sense any signal, cells must distinguish between the signal and the background noise. for the chemical senses, the signal is the binding of a chemical to a receptor on the sensing cells. at the molecular level, background noise corresponds to thermal fluctuations in the movement of molecules. the equipartition theorem of thermodynamics states that each mode of motion at equilibrium has the energy ½ kt, where k is boltzmann’s constant and t is the temperature in °k. k = 1.38 x10-23 joule °k-1 molecule-1