The first law of thermodynamics states that matter can be neither created nor destroyed. It is only converted from one form of energy into another. This energy conversion isn’t 100 percent efficient. Some of it is converted into an unusable form. This creates entropy, which is a measure of disorder. The second law of thermodynamics states that with each energy conversion, entropy increases.
Living things are considered highly ordered with low entropy. To remain this way, energy must be expended. Over time, the biological processes that maintain this order become less and less efficient. This causes an increase in entropy. Eventually, the process will become so inefficient that an organism dies.
The first law is demonstrated through the biological processes themselves. The energy needed to maintain this order is derived from energy conversions. Examples of this are photosynthesis, aerobic respiration, and anaerobic respiration. Photosynthesis converts light energy into chemical energy. Both forms of respiration convert chemical energy into ATP molecules, which is the currency of important biochemical reactions such as DNA synthesis.