Yet, organisms maintain a stable structure over long periods of time. This stability of large structures with the molecular components constantly replaced and regenerated is called homeostasis, meaning they maintain a status quo. Living organisms maintain a state of metabolic homeostasis which can be viewed as a steady-state throughput of energy to sustain body function, structure, and information. Both chemical energy and molecular building blocks are extracted from the nutrients in our diet and are used to form macromolecules like proteins, DNA, polysaccharides, and membranes. These macromolecular structures in turn control nutrient uptake, metabolism, and excretion.
Metabolism is a dynamic process of energy conversion in cells of living organisms.
In a most abstract representation, cellular metabolism is a spatial and temporal network of chemical reactions and molecular interactions close to, but never quite at chemical equilibrium. Erwin Schroedinger asked for a physical and chemical accountability of the spatial and temporal processes occurring within the boundaries of a cell. As he made vividly clear, he deemed contemporary physics inappropriate to explain molecular mechanisms of a cell. Physical natural laws are exact only for large and very simple systems, like highly symmetric salt crystals. They explain the behavior of large numbers of identical molecules, while they cannot describe the exact behavior of such individual molecules, but only give probabilities.