Characteristics of Life
If biology is the study of life, then it is natural to ask: What is life? There is no one definition of life that can encompass all living things. However, there are certain characteristics that all living things share:
- Order and organization: The basic unit of life is the cell. It is capable of performing all activities of life. For single-celled organisms, this is the limit of their organization. For multicellular organisms, cells may be arranged in tissues, tissues arranged in organs, and organs arranged in systems. Living things are further organized into populations, communities, ecosystems and, ultimately, the biosphere (the combined regions of the earth in which organisms can live). A corollary to this topic is the organization and structure of the genetic material: all living things have nucleic acids as the storage mechanism for genetic information.
- Growth and development: All living things grow and develop during their life. This may be as simple as a bacterium that increases in size or as complex as a fertilized egg that develops into an elaborate, multicellular organism.
- Reproduction: Organisms must reproduce in order for the species to survive. The exact mode of reproduction may be different
(for example, asexual verses sexual reproduction), but the outcome is the same: an increase in the number of organisms.
- Energy metabolism: All living things require energy to survive. Various processes are necessary in order to supply this energy. First of all, organisms must gain nutrition: those that can make their own food are called autotrophs, all others are called heterotrophs. The nutrients must be converted into energy, which includes the process of respiration. Finally, waste products must be eliminated.
- Stimuli response and homeostasis: The ability to respond to the environment, whether it be the external or the internal environment, is a vital function in all living things. Organisms must regulate their life processes based on what is happening in the environment.
- Evolution: The ability to change, to mutate, is an important characteristic of life. Were it not for this ability, the vast diversity of life would not exist on this planet. For that matter, no life would exist at all.