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Biology

2007 Schools Wikipedia Selection. Related subjects: General Biology

   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 energy.
   Escherichia coli Tree fern
   Goliath beetle   Gazelle
   Biology studies the variety of life (clockwise from top-left) E. coli,
   tree fern, gazelle, Goliath beetle

   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.

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.

Universality: Biochemistry, cells, and the genetic code

   Schematic representation of DNA, the primary genetic material.
   Enlarge
   Schematic representation of DNA, the primary genetic material.

   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.

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).

   In recent years, evolution and other branches of science have come
   under attack by people who disagree with scientific findings regarding
   the origins and diversity of life, favoring instead religious
   explanations. See Creation-evolution controversy for more information.

Diversity

   A phylogenetic tree of all living things, based on rRNA gene data,
   showing the separation of the three domains bacteria, archaea, and
   eukaryotes as described initially by Carl Woese. Trees constructed with
   other genes are generally similar, although they may place some
   early-branching groups very differently, presumably owing to rapid rRNA
   evolution. The exact relationships of the three domains are still being
   debated.
   Enlarge
   A phylogenetic tree of all living things, based on rRNA gene data,
   showing the separation of the three domains bacteria, archaea, and
   eukaryotes as described initially by Carl Woese. Trees constructed with
   other genes are generally similar, although they may place some
   early-branching groups very differently, presumably owing to rapid rRNA
   evolution. The exact relationships of the three domains are still being
   debated.

   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:

          Monera -- Protista -- Fungi -- Plantae -- Animalia

   However, many scientists now consider this five-kingdom system to be
   outdated. Modern alternative classification systems generally begin
   with the three-domain system:

          Archaea (originally Archaebacteria) -- Bacteria (originally
          Eubacteria) -- Eukaryota

   These domains reflect whether the cells have nuclei or not, as well as
   differences in the cell exteriors.

   Further, each kingdom is broken down continuously until each species is
   separately classified. The order is 1) Kingdom, 2) Phylum, 3) Class, 4)
   Order, 5) Family, 6) Genus, 7) Species. The scientific name of an
   organism is obtained from its Genus and Species. For example, humans
   would be listed as Homo sapiens. Homo would be the Genus and Sapiens is
   the species. Whenever writing the scientific name of an organism it is
   proper to capitalize the first letter in the genus and put all of the
   species in lowercase; in addition the entire term would be put in
   italics. The term used for classification is called Taxonomy.

   There is also a series of intracellular parasites that are
   progressively "less alive" in terms of metabolic activity:

          Viruses -- Viroids -- Prions

Continuity

   Up into the 19th century, it was commonly believed that life forms
   could appear spontaneously under certain conditions (see abiogenesis).
   This misconception was challenged by William Harvey's diction that "all
   life [is] from [an] egg" (from the Latin " Omne vivum ex ovo"), a
   foundational concept of modern biology. It simply means that there is
   an unbroken continuity of life from its initial origin to the present
   time.

   A group of organisms shares a common descent if they share a common
   ancestor. All organisms on the Earth have been and are descended from a
   common ancestor or an ancestral gene pool. This last universal common
   ancestor of all organisms is believed to have appeared about 3.5
   billion years ago. Biologists generally regard the universality of the
   genetic code as definitive evidence in favour of the theory of
   universal common descent (UCD) for all bacteria, archaea, and
   eukaryotes (see: origin of life).

Homeostasis

   Homeostasis is the ability of an open system to regulate its internal
   environment to maintain a stable condition by means of multiple dynamic
   equilibrium adjustments controlled by interrelated regulation
   mechanisms. All living organisms, whether unicellular or multicellular,
   exhibit homeostasis. Homeostasis manifests itself at the cellular level
   through the maintenance of a stable internal acidity ( pH); at the
   organismic level, warm-blooded animals maintain a constant internal
   body temperature; and at the level of the ecosystem, as when
   atmospheric carbon dioxide levels rise and plants are theoretically
   able to grow healthier and remove more of the gas from the atmosphere.
   Tissues and organs can also maintain homeostasis.

Interactions

   Mutual symbiosis between clownfish of the genus Amphiprion that dwell
   among the tentacles of tropical sea anemones. The territorial fish
   protects the anemone from anemone-eating fish, and in turn the stinging
   tentacles of the anemone protects the clown fish from its predators
   Enlarge
   Mutual symbiosis between clownfish of the genus Amphiprion that dwell
   among the tentacles of tropical sea anemones. The territorial fish
   protects the anemone from anemone-eating fish, and in turn the stinging
   tentacles of the anemone protects the clown fish from its predators

   Every living thing interacts with other organisms and its environment.
   One reason that biological systems can be difficult to study is that so
   many different interactions with other organisms and the environment
   are possible, even on the smallest of scales. A microscopic bacterium
   responding to a local sugar gradient is responding to its environment
   as much as a lion is responding to its environment when it searches for
   food in the African savannah. For any given species, behaviors can be
   co-operative, aggressive, parasitic or symbiotic. Matters become more
   complex when two or more different species interact in an ecosystem.
   Studies of this type are the province of ecology.

Scope

   Biology has become such a vast research enterprise that it is not
   generally regarded as a single discipline, but as a number of clustered
   sub-disciplines. This article considers four broad groupings. The first
   group consists of those disciplines that study the basic structures of
   living systems: cells, genes etc.; the second group considers the
   operation of these structures at the level of tissues, organs, and
   bodies; the third group considers organisms and their histories; the
   final constellation of disciplines focuses on their interactions. It is
   important to note, however, that these boundaries, groupings, and
   descriptions are a simplified characterization of biological research.
   In reality, the boundaries between disciplines are fluid, and most
   disciplines frequently borrow techniques from each other. For example,
   evolutionary biology leans heavily on techniques from molecular biology
   to determine DNA sequences, which assist in understanding the genetic
   variation of a population; and physiology borrows extensively from cell
   biology in describing the function of organ systems.

Structure of life

   Molecular biology is the study of biology at a molecular level. This
   field overlaps with other areas of biology, particularly with genetics
   and biochemistry. Molecular biology chiefly concerns itself with
   understanding the interactions between the various systems of a cell,
   including the interrelationship of DNA, RNA, and protein synthesis and
   learning how these interactions are regulated.

   Cell biology studies the physiological properties of cells, as well as
   their behaviors, interactions, and environment. This is done both on a
   microscopic and molecular level. Cell biology researches both
   single-celled organisms like bacteria and specialized cells in
   multicellular organisms like humans.

   Understanding cell composition and how they function is fundamental to
   all of the biological sciences. Appreciating the similarities and
   differences between cell types is particularly important in the fields
   of cell and molecular biology. These fundamental similarities and
   differences provide a unifying theme, allowing the principles learned
   from studying one cell type to be extrapolated and generalized to other
   cell types.

   Genetics is the science of genes, heredity, and the variation of
   organisms. In modern research, genetics provides important tools in the
   investigation of the function of a particular gene, or the analysis of
   genetic interactions. Within organisms, genetic information generally
   is carried in chromosomes, where it is represented in the chemical
   structure of particular DNA molecules.

   Genes encode the information necessary for synthesizing proteins, which
   in turn play a large role in influencing (though, in many instances,
   not completely determining) the final phenotype of the organism.

   Developmental biology studies the process by which organisms grow and
   develop. Originating in embryology, modern developmental biology
   studies the genetic control of cell growth, differentiation, and "
   morphogenesis," which is the process that gives rise to tissues,
   organs, and anatomy. Model organisms for developmental biology include
   the round worm Caenorhabditis elegans, the fruit fly Drosophila
   melanogaster, the zebrafish Brachydanio rerio, the mouse Mus musculus,
   and the weed Arabidopsis thaliana.

Physiology of organisms

   Main articles: Physiology, Anatomy

   Physiology studies the mechanical, physical, and biochemical processes
   of living organisms by attempting to understand how all of the
   structures function as a whole. The theme of "structure to function" is
   central to biology. Physiological studies have traditionally been
   divided into plant physiology and animal physiology, but the principles
   of physiology are universal, no matter what particular organism is
   being studied. For example, what is learned about the physiology of
   yeast cells can also apply to human cells. The field of animal
   physiology extends the tools and methods of human physiology to
   non-human species. Plant physiology also borrows techniques from both
   fields.

   Anatomy is an important branch of physiology and considers how organ
   systems in animals, such as the nervous, immune, endocrine,
   respiratory, and circulatory systems, function and interact. The study
   of these systems is shared with medically oriented disciplines such as
   neurology and immunology.

Diversity and evolution of organisms

   In population genetics the evolution of a population of organisms is
   sometimes depicted as if travelling on a fitness landscape. The arrows
   indicate the preferred flow of a population on the landscape, and the
   points A, B, and C are local optima. The red ball indicates a
   population that moves from a very low fitness value to the top of a
   peak
   Enlarge
   In population genetics the evolution of a population of organisms is
   sometimes depicted as if travelling on a fitness landscape. The arrows
   indicate the preferred flow of a population on the landscape, and the
   points A, B, and C are local optima. The red ball indicates a
   population that moves from a very low fitness value to the top of a
   peak

   Main articles: Evolutionary biology, Biodiversity, Botany, Zoology

   Evolutionary biology is concerned with the origin and descent of
   species, as well as their change over time, and includes scientists
   from many taxonomically-oriented disciplines. For example, it generally
   involves scientists who have special training in particular organisms
   such as mammalogy, ornithology, or herpetology, but use those organisms
   as systems to answer general questions about evolution. Evolutionary
   biology is mainly based on paleontology, which uses the fossil record
   to answer questions about the mode and tempo of evolution, as well as
   the developments in areas such as population genetics and evolutionary
   theory. In the 1990s, developmental biology re-entered evolutionary
   biology from its initial exclusion from the modern synthesis through
   the study of evolutionary developmental biology. Related fields which
   are often considered part of evolutionary biology are phylogenetics,
   systematics, and taxonomy.

   The two major traditional taxonomically-oriented disciplines are botany
   and zoology. Botany is the scientific study of plants. Botany covers a
   wide range of scientific disciplines that study the growth,
   reproduction, metabolism, development, diseases, and evolution of plant
   life. Zoology involves the study of animals, including the study of
   their physiology within the fields of anatomy and embryology. The
   common genetic and developmental mechanisms of animals and plants is
   studied in molecular biology, molecular genetics, and developmental
   biology. The ecology of animals is covered under behavioural ecology
   and other fields.

Classification of life

   The dominant classification system is called Linnaean taxonomy, which
   includes ranks and binomial nomenclature. How organisms are named is
   governed by international agreements such as the International Code of
   Botanical Nomenclature (ICBN), the International Code of Zoological
   Nomenclature (ICZN), and the International Code of Nomenclature of
   Bacteria (ICNB). A fourth Draft BioCode was published in 1997 in an
   attempt to standardize naming in these three areas, but it has yet to
   be formally adopted. The Virus cInternational Code of Virus
   Classification and Nomenclature (ICVCN) remains outside the BioCode.

Interactions of organisms

   A food web, a generalization of the food chain, depicting the complex
   interrelationships among organisms in an ecosystem.
   A food web, a generalization of the food chain, depicting the complex
   interrelationships among organisms in an ecosystem.

   Main articles: Ecology, Ethology, Behaviour, Biogeography

   Ecology studies the distribution and abundance of living organisms, and
   the interactions between organisms and their environment. The
   environment of an organism includes both its habitat, which can be
   described as the sum of local abiotic factors such as climate and
   geology, as well as the other the organisms that share its habitat.
   Ecological systems are studied at several different levels, from
   individuals and populations to ecosystems and the biosphere. As can be
   surmised, ecology is a science that draws on several disciplines.

   Ethology studies animal behaviour (particularly of social animals such
   as primates and canids), and is sometimes considered a branch of
   zoology. Ethologists have been particularly concerned with the
   evolution of behavior and the understanding of behaviour in terms of
   the theory of natural selection. In one sense, the first modern
   ethologist was Charles Darwin, whose book The expression of the
   emotions in animals and men influenced many ethologists.

   Biogeography studies the spatial distribution of organisms on the
   Earth, focusing on topics like plate tectonics, climate change,
   dispersal and migration, and cladistics.

Etymology

   Formed by combining the Greek βίος (bios), meaning 'life', and λόγος
   (logos), meaning 'study of', the word "biology" in its modern sense
   seems to have been introduced independently by Gottfried Reinhold
   Treviranus (Biologie oder Philosophie der lebenden Natur, 1802) and by
   Jean-Baptiste Lamarck (Hydrogéologie, 1802). The word itself is
   sometimes said to have been coined in 1800 by Karl Friedrich Burdach,
   but it appears in the title of Volume 3 of Michael Christoph Hanov's
   Philosophiae naturalis sive physicae dogmaticae: Geologia, biologia,
   phytologia generalis et dendrologia, published in 1766.

History

   Major discoveries in biology include:
     * Cell theory
     * Germ theory of disease
     * Genetics
     * Evolution
     * DNA

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