In studying energy, scientists use the term “system” to refer to the matter and its environment involved in energy transfers. Everything outside of the system is the surroundings. Single cells are biological systems. We can think of systems as having a certain amount of order. It takes energy to make a system more ordered. The more ordered a system, the lower its entropy. Entropy is a measure of a system's disorder. As a system becomes more disordered, the lower its energy and the higher its entropy.
The laws of thermodynamics are a series of laws that describe the properties and processes of energy transfer. The first law states that the total amount of energy in the universe is constant. This means that energy cannot be created or destroyed, only transferred or transformed. The second law of thermodynamics states that every energy transfer involves some loss of energy in an unusable form, such as heat energy, resulting in a more disordered system. In other words, no energy transfer is completely efficient, and all transfers trend toward disorder.