Where Does "The System" Begin and End? A Partial Description of Nature from That Which is Conserved.
Descriptions of Nature depend on defining The System, and defining what is "conserved" in terms of what remains INSIDE The System following some reaction or experiment or event, and what is "not conserved" because it passes OUTSIDE The System, into The Surroundings ("the rest of the universe" that is not The System).
Living Systems must maintain their separation from their surroundings, but in order to do this, they depend on the surroundings from which they are separated. Aerobic creatures are immersed in oxygen with evolved systems that automatically process it without necessary thought or competition or cooperation. We literally move through it like fish in water, we swim in an oxygenated environment that our bodies know what to do with.
Food and water are different. Dependence on food and water impose a different kind of dependence on the surroundings that tells us something about how Nature is, and how we are.
My working understanding is that all life must overcome a separation between what it wants, needs, knows, predicts, expects and its actual experience to remain uniquely separated from its surroundings as part of a continuous intervention on the evolution of nature. I believe physical dependence on transcending this separation is what life is.