In biology, energy is king. Solar energy is at the core of nearly every ecosystem on the planet, and this energy from the sun drives everything from the complexity of a food web to the cellular processes that replicate the genetic code passed from one generation to the next. Deprived of the energy required to do work, the essence of an organism, its “livingness,” comes to an end.
In living systems, energy is only half of the story. For life to exist, molecular vessels (organisms) must be modified, organized and assembled in ways that can harness the energy. These pliable molecules are commonly referred as biological nutrients.
A fundamental concept to all biological systems requires that energy flows while nutrients are cycled. Energetics are subject to the physical laws of nature, and life can only exist if it obeys these laws. The ”first law of thermodynamics” informs us about energy’s limits. Energy in a biological system is conserved but not recycled. This energy is transferred and transformed from molecules to motion, from motion to molecules, but can not be created nor destroyed. The energy trapped by the molecules in our food is transferred to packets of chemical energy that drive our cellular processes. Simultaneously, some of the energy from each meal results in the generation of heat, or the vibration of molecules, that will increase the entropy in a living system. This energy is not lost, it just flows from one state to another.
In contrast to the energy on the planet, nutrients are limited and must be recycled. Without the cycling of carbon, oxygen and nitrogen the resources required to build an organism will diminish. One of the great harmonies of living systems is the ability to harness energy to order molecules in a manner that can sustain itself for a finite period of time. However, as this molecular order is subject to the stresses of the environment, an ecosystem and time, it becomes less efficient and less capable of harnessing the energy required to remain whole. It is at this point that death ends the cycle inherent in every life. To this biologist, death is nothing more than the completion of a life that includes the wonderful serendipity of unique molecular interactions on this planet we call Earth.
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