Life Characteristics

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From the biology textbooks there is this list of agreed upon characteristics for life:

1. Organization. All living things are organized and structured at the molecular, cellular, tissue, organ, system, and individual level. Organization also exists at levels beyond the individual, such as populations, communities, and ecosystems.

2. Maintenance/Metabolism. To overcome entropy (the tendency of a system to become more disorganized and less complex), living things use energy to maintain homeostasis (i.e., maintain their sameness; a constant, structured internal environment). Metabolism is a collective term to describe the chemical and physical reactions that result in life.

3. Growth. Living things grow. The size and shape of an individual are determined by its genetic makeup and by the environment.

4. Response to Stimuli. Living things react to information that comes from outside or inside themselves.

5. Reproduction. Individuals reproduce themselves. Life also reproduces itself at the subcellular and cellular levels. In some instances, genetic information is altered. These mutations and genetic recombinations give rise to variations in a species.

6. Variation. Living things are varied because of mutation and genetic recombinations. Variations may affect an individual's appearance or chemical makeup and many genetic variations are passed from one generation to the next.

7. Adaption. Living things adapt to changes in their environment.

Items 2 and 3 are related. Life grows by creating more and more order. Since entropy is decreased (the amount of structure and complexity is increased), life requires an input of energy. Life gains local structure at the expense of seemingly chaotic surroundings on a large scale. Items 5, 6, and 7 are related. Life reproduces---complex structures reproduce themselves. Life changes itself in response to natural selection on the macroscopic level and to changes in DNA on the microscopic level.

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last updated: June 1, 2007