Life on Our Planet
The Classification of Earthly Life
LIFE (Biota) is a characteristic that distinguishes objects that have self-sustaining biological processes ("alive," "living"), from those which do not — either because such functions have ceased (death), or else because they lack such functions and are classified as "inanimate."
In biology, the science that studies living organisms, "life" is the condition which distinguishes active organisms from inorganic matter, including the capacity for growth, functional activity and the continual change preceding death. A diverse array of living organisms (life forms) can be found in the biosphere on Earth, and properties common to these organisms -- the eukaryotes (plants, animals, fungi, and protists), archaea, and bacteria — are a carbon- and water-based cellular form with complex organization and heritable genetic information. Living organisms undergo metabolism, maintain homeostasis, possess a capacity to grow, respond to stimuli, reproduce and, through natural selection, adapt to their environment in successive generations. More complex living organisms can communicate through various means.
Viruses are most often considered replicators rather than forms of life. They have been described as "organisms at the edge of life", since they possess genes, evolve by natural selection, and replicate by creating multiple copies of themselves through self-assembly. However, viruses do not metabolise and require a host cell to make new products. Virus self-assembly within host cells has implications for the study of the origin of life, as it may support the hypothesis that life could have started as self-assembling organic molecules.
Biological Classification (or scientific classification) in biology, is a method by which biologists group and categorize organisms by biological type, such as genus or species. Biological classification is a form of scientific taxonomy, but should be distinguished from folk taxonomy, which lacks scientific basis. Modern biological classification has its root in the work of Carolus Linnaeus, who grouped species according to shared physical characteristics. These groupings since have been revised to improve consistency with the Darwinian principle of common descent. Molecular phylogenetics, which uses DNA sequences as data, has driven many recent revisions and is likely to continue to do so. Biological classification belongs to the science of biological systematics.