The cell is the atom of life.
Letís start with observations.
1. Microbes are the smallest cells living an independent life, observed in nature.
1a. Viruses are smaller but cannot live independently.
2. The complexity of the smallest microbe is immense.
2a. The smallest microbe on earth illustrates what such a minimal complexity might be. It might be regarded as an atom of life. When divided into its parts it ceases to exist. (Atom in Greek means indivisible)
2b† Despite ongoing research nobody succeeded to generate such a complexity from organic or inorganic molecules.
3. Most (if not all) microbes do not live isolated, they live in populations called bio-films which by themselves are† living organisms. An isolated microorganism is only a temporary (transient) state.
4. Properties of the atom of life4a Is an open system exchanging matter and energy with the environment.
4b Its structure is oriented. In other words it is a set of oriented processes.
4c Despite †an ongoing turnover† it maintains its appearance. This feature is known as steady state, homeostasis or homeorhesis.
4d It is optimal.
4e It reproduces.
Properties 4b,4c and 4d are collectively called Wisdom of the Body (WOB).
In other words, the atom of life is an open system with a WOB.
The proliferon is the simplest artificial construct illustrating these properties.
5. Whenever atoms of life aggregate they create open systems with a WOB. For instance bio-films are also open systems with a WOB and so are we.