Entropy is a measure of probability and the "disorder" of a system. Disorder refers to is really the number of different microscopic states a system can be in, given that the system has a particular fixed composition, volume, energy, pressure, and temperature. the exact definition is Entropy = (Boltzmann's constant k) x logarithm of number of possible states = k log(N). The first law of thermodynamics defines the relationship between the various forms of energy present in a system (kinetic and potential), the work which the system performs and the transfer of heat. We can imagine thermodynamic processes which conserve energy but which never occur in nature. For example, if we bring a hot object into contact with a cold object, we observe that the hot object cools down and the cold object heats up until an equilibrium is reached. The transfer of heat goes from the hot object to the cold object. According to the second law of thermodynamics, in any process that involves a cycle, the entropy of the system will either stay the same or increase. When the cyclic process is reversible then the entropy will not change. When the process is irreversible, then entropy will increases. The second law states that there exists a useful state variable called entropy S. The change in entropy delta S is equal to the heat transfer delta Q divided by the temperature T. delta S = delta Q / T Order can be produced with an expenditure of energy, and the order associated with life on the earth is produced with the aid of energy from the sun. For example, plants use energy from the sun in tiny energy factories called chloroplasts Using chlorophyll in the process called photosynthesis, they convert the sun's energy into storable form in ordered sugar molecules. In this way, carbon and water in a more disordered state are combined to form the more ordered sugar molecules. In animal systems there are also small structures within the cells called mitochondria which use the energy stored in sugar molecules from food to form more highly ordered structures.