2.2 Nature of Life

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Physics of Life

Although living systems obey the laws of physics and chemistry, according to Professor Ellis, the notion of function or purpose differentiates biology from other natural sciences.
Organisms exist to reproduce, whereas rocks and stars have no purpose. Selection for function has produced the living cell, with a unique set of properties that distinguish it from inanimate systems of interacting molecules.
Cells exist far from thermal equilibrium by harvesting energy from their environment.
Cells are composed of thousands of different types of molecules. They contain information for their survival and reproduction, in the form of their DNA.

Processes of Life

Homeostasis: regulation of the internal environment to maintain a constant stat
Organization: structural composition of one or more cells—the basic units of life
Metabolism: transformation of energy to maintain internal organization and do work
Growth: A growing organism increases in size and organization of its parts through developmental processes
Adaptation: the ability to change over time in response to the environment
Response to stimuli: ranging from reactions of a unicellular organism to external chemicals to complex reactions involving all the senses of multicellular organisms
Reproduction: the ability to produce new individual organisms

All these processes have underlying physical and chemical bases, and these lifeforms adapt life to physical, ecological and social environments, via sensory, signaling, and control mechanisms, which use energy.

Information Usage Logic

All biological life is based on function or purpose, and at higher levels, intention.
Organisms acquire, filter, classify, and store information, which allows them to predict future outcomes and act purposefully.
Information usage is a logical process and can be realized through different physical processes.
Organisms use information at multiple levels of a logical hierarchy based on contextual choices of the form
```
{GIVEN CONTEXT C, IF T(X) THEN F1(Y), ELSE F2(Z)}
```
where T(X), F1(Y) and F2(Z) are arbitrary truth functions of variables X, Y, Z (where T = True and F = False), including logical operations (AND, OR, NOT, NOR, etc).