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[5] [6] [7] This is complicated by a lack of knowledge of the characteristics of living entities, if any, that may have developed outside Earth. [8] [9] Philosophical definitions of life have also been put forward, with similar difficulties on how to distinguish living things from the non-living. [10]
The classification of living things into animals and plants is an ancient one. Aristotle (384–322 BC) classified animal species in his History of Animals, while his pupil Theophrastus (c. 371 –c. 287 BC) wrote a parallel work, the Historia Plantarum, on plants. [7]
Living systems. Living systems are life forms (or, more colloquially known as living things) treated as a system. They are said to be open self-organizing and said to interact with their environment. These systems are maintained by flows of information, energy and matter. Multiple theories of living systems have been proposed.
e. In biology, taxonomy (from Ancient Greek τάξις ( taxis) 'arrangement' and -νομία ( -nomia) ' method ') is the scientific study of naming, defining ( circumscribing) and classifying groups of biological organisms based on shared characteristics. Organisms are grouped into taxa (singular: taxon) and these groups are given a taxonomic ...
Organism. An organism is defined in a medical dictionary as any living thing that functions as an individual. [ 1] Such a definition raises more problems than it solves, not least because the concept of an individual is also difficult. Many criteria, few of them widely accepted, have been proposed to define what is an organism.
Animals have several characteristics that set them apart from other living things. Animals are eukaryotic and multicellular. [14] Unlike plants and algae, which produce their own nutrients, [15] animals are heterotrophic, [16] [17] feeding on organic material and digesting it internally. [18] With very few exceptions, animals respire aerobically.
All known living things are made up of one or more cells [13] All living cells arise from pre-existing cells by division. The cell is the fundamental unit of structure and function in all living organisms. [14] The activity of an organism depends on the total activity of independent cells. [15] Energy flow (metabolism and biochemistry) occurs ...
The particular form of biological classification (taxonomy) set up by Carl Linnaeus, as set forth in his Systema Naturae (1735) and subsequent works. In the taxonomy of Linnaeus there are three kingdoms, divided into classes, and the classes divided into lower ranks in a hierarchical order. A term for rank-based classification of organisms, in ...