<Dl> <Dd> E = h c λ = h ν, (\ displaystyle E = (\ frac (hc) (\ lambda)) = h \ nu,) </Dd> </Dl> <Dd> E = h c λ = h ν, (\ displaystyle E = (\ frac (hc) (\ lambda)) = h \ nu,) </Dd> <P> where h is the Planck constant (6.63 x10 Js) and c is the speed of light (2.998 x10 m / s). Plants trap this energy from the sunlight and undergo photosynthesis, effectively converting solar energy into chemical energy . To transfer the energy once again, animals will feed on plants and use the energy of digested plant materials to create biological macromolecules . </P> <P> The First Law of Thermodynamics is a statement of the conservation of energy; though it can be changed from one form to another, energy can be neither created nor destroyed . From the first law, a principle called Hess's Law arises . Hess's Law states that the heat absorbed or evolved in a given reaction must always be constant and independent of the manner in which the reaction takes place . Although some intermediate reactions may be endothermic and others may be exothermic, the total heat exchange is equal to the heat exchange had the process occurred directly . This principle is the basis for the calorimeter, a device used to determine the amount of heat in a chemical reaction . Since all incoming energy enters the body as food and is ultimately oxidized, the total heat production may be estimated by measuring the heat produced by the oxidation of food in a calorimeter . This heat is expressed in kilocalories, which are the common unit of food energy found on nutrition labels . </P>

Application of laws of thermodynamics in biological system