Converting energy from one form to another is governed by the laws of thermodynamics. The first law states that energy cannot be created or destroyed, it can just change form. This means that life must rely on an outside source of energy, namely the sun. The second law states that energy cannot be changed from one form to another without a loss of usable energy. This means that in an energy conversion only some of the original energy ends up in the new form; the rest is lost as heat. The second law also says that systems tend towards a state of disorder. This means that systems, such as living things, run down if not continually supplied with energy.