organisme

An organism is an individual living unit that exhibits the characteristics of life. In biology, organisms are typically defined as systems capable of metabolism, growth, development, reproduction, response to stimuli, and the maintenance of internal stability (homeostasis). They use energy and materials from the environment to sustain their structure and activities and to adapt to changing conditions. In languages such as English and French, the corresponding terms are organism and organisme, respectively.

Most organisms are composed of cells. In multicellular organisms, cells organize into tissues, organs, and organ systems that coordinate to perform the organism's functions. The cell theory states that all living organisms are composed of cells and that new cells arise from pre-existing cells. Unicellular organisms carry out all life processes within a single cell.

Organisms vary greatly in size, form, and lifestyle. They can be autotrophic, obtaining energy from light or chemical sources, or heterotrophic, deriving energy from other organisms. They reproduce sexually or asexually, and their populations evolve over generations through genetic variation and natural selection. Organisms interact with their environments through metabolism, respiration, waste removal, and signaling.

Taxonomically, organisms are classified into taxa such as domains, kingdoms, phyla, and species, with species representing interbreeding natural populations. The concept of an organism can be nuanced; some entities, notably viruses, carry genetic material and reproduce but lack independent metabolism and thus are not universally regarded as organisms outside a host.