Biology
From Wikipedia, the free encyclopedia
Biology (from Greek βίος λόγος, see below) is the branch of science dealing with the study of living organisms. It is concerned with the characteristics, classification, and behaviors of organisms, how species come into existence, and the interactions they have with each other and with the natural environment. Biology encompasses a broad spectrum of academic fields that are often viewed as independent disciplines. However, together they address phenomena related to living organisms (biological phenomena) over a wide range of scales, from biophysics to ecology. All concepts in biology are subject to the same laws that other branches of science obey, such as the laws of thermodynamics and conservation of mass.
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At the organism level, biology has partially explained phenomena such as birth, growth, aging, death and decay of living organisms, similarities between offspring and their parents (heredity) and flowering of plants which have puzzled humanity throughout history. Other phenomena, such as lactation, metamorphosis, egg-hatching, healing, and tropism have been addressed. On a wider scale of time and space, biologists have studied domestication of animals and plants, the wide variety of living organisms (biodiversity), changes in living organisms over many generations (evolution), extinction, speciation, social behaviour among animals, etc.
While botany encompasses the study of plants, zoology is the branch of science that is concerned about the study of animals and anthropology is the branch of biology which studies human beings. However, at the molecular scale, life is studied in the disciplines of molecular biology, biochemistry, and molecular genetics. More fundamental than these fields is biophysics which deals with energy within biological systems. At the next level, that of the cell, it is studied in cell biology. At the multicellular scale, it is examined in physiology, anatomy, and histology. Developmental biology studies life at the level of an individual organism's development or ontogeny. Moving up the scale towards more than one organism, genetics considers how heredity works between parent and offspring. Ethology considers the behaviour of organisms in their natural environment. Population genetics looks at the level of an entire population, and systematics considers the multi-species scale of lineages. Interdependent populations and their habitats are examined in ecology and evolutionary biology. A speculative new field is astrobiology (or xenobiology), which examines the possibility of life beyond the Earth.
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[edit] Principles
Biology does not usually describe systems in terms of objects which obey immutable physical laws described by mathematics. Biological systems have predictable statistical tendencies to behave in certain ways, but these tendencies are usually not as concrete as those described in subjects such as physics. However, biology is still subject to the same physical laws of the universe such as thermodynamics and conservation of mass.
The biological sciences are characterized and unified by several major underlying principles and concepts: universality, evolution, diversity, continuity, genetics, homeostasis, and interactions.
[edit] Universality: Biochemistry, cells, and the genetic code
Some striking examples of biological universality include life's carbon-based biochemistry and its ability to pass on characteristics via genetic material, using a DNA and RNA based genetic code with only minor variations across all living things.
Another universal principle is that all organisms (that is, all forms of life on Earth except for viruses) are made of cells. Similarly, all organisms share common developmental processes.
[edit] Evolution
The central organizing concept in biology is that all life has a common origin and has changed and developed through the process of evolution (see Common descent). This has led to the striking similarity of units and processes discussed in the previous section. Charles Darwin established evolution as a viable theory by articulating its driving force, natural selection (Alfred Russel Wallace is recognized as the co-discoverer of this concept). Genetic drift was embraced as an additional mechanism of evolutionary development in the modern synthesis of the theory.
The evolutionary history of a species— which describes the characteristics of the various species from which it descended— together with its genealogical relationship to every other species is called its phylogeny. Widely varied approaches to biology generate information about phylogeny. These include the comparisons of DNA sequences conducted within molecular biology or genomics, and comparisons of fossils or other records of ancient organisms in paleontology. Biologists organize and analyze evolutionary relationships through various methods, including phylogenetics, phenetics, and cladistics (The major events in the evolution of life, as biologists currently understand them, are summarized on this evolutionary timeline).
[edit] Diversity
Classification is the province of the disciplines of systematics and taxonomy. Taxonomy places organisms in groups called taxa, while systematics seeks to define their relationships with each other. This classification technique has evolved to reflect advances in cladistics and genetics, shifting the focus from physical similarities and shared characteristics to phylogenetics.
Traditionally, living things have been divided into five kingdoms:
However, many scientists now consider this five-kingdom system to be outdated. Modern alternative classification systems generally begin with the three-domain system:
