Biocrawler:Wikiportal/Biology

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Structure of life

Contents 1 Structure of life 1.1 Classification of life 2 Principles of biology 2.1 Biochemistry 2.2 Evolution 2.3 Diversity 2.4 Continuity 3 Description 4 History of the word "biology" 5 Related topics 6 Further reading

Molecular biology is the study of biology at a molecular level. The field overlaps with other areas of biology, particularly 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 the composition of cells and how cells works is fundamental to all of the biological sciences. Appreciating the similarities and differences between cell types is particularly important to 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, e.g. 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, although, in many instances, do not completely determine, the final phenotype of the organism.

Developmental biology studies the process by which organisms grow and develop. Originating in embryology, today 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.

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 the three areas, but it does not appear to have yet been formally adopted. The International Code of Virus Classification and Nomenclature (ICVCN) remains outside the BioCode.

Principles of biology

While biology is unlike physics in that it does not usually describe biological systems in terms of objects which obey immutable physical laws described by mathematics, it is nevertheless characterized by several major principles and concepts which include: universality, evolution, diversity, continuity, homeostasis and interactions.

Biochemistry

There are many universal units and common processes that are fundamental to the known forms of life. For example all forms of life consist of cells, which in turn, are based on a common carbon-based biochemistry. All organisms pass on their heredity via the genetic material which is based upon the nucleic acid DNA using a universal genetic code. In development the theme of universal processes is also present, for example in most metazoan organisms the basic steps of the early embryo development share similar morphological stages and include similar genes.

Evolution

One of the central, organizing concepts in biology is that all life has descended from a common origin through a process of evolution. Indeed, it is one of the reasons that biological organisms exhibit 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 Russell Wallace is commonly recognized as the co-discoverer of this concept). Genetic drift was embraced as an additional mechanism in the so-called modern synthesis. The evolutionary history of a species—which tells 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. Major events in the evolution of life, as biologists currently understand them, are summarized on this evolutionary timeline.

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.]]

Despite the underlying unity, life exhibits an astonishing wide diversity in morphology, behavior and life histories. In order to grapple with this diversity, biologists attempt to classify all living things. This scientific classification should reflect the evolutionary trees (phylogenetic trees) of the different organisms. Such classifications are the province of the disciplines of systematics and taxonomy. Taxonomy puts organisms in groups called taxa, while systematics seeks their relationships.

Traditionally, living things were divided into five kingdoms:

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

However, this five-kingdom system is now considered by many to be outdated. More modern alternatives generally begin with the three-domain system:

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

These domains reflect whether cells have nuclei or not as well as differences in cell exteriors. There is also a series of intracellular "parasites" that are progressively less alive in terms of being metabolically active:

Viruses -- Viroids -- Prions

Continuity

A group of organisms is said to have common descent if they have a common ancestor. All existing organisms on Earth are descended from a common ancestor or ancestral gene pool. This "last universal common ancestor, that is, the most recent common ancestor of all organisms, is believed to have appeared about 3.5 billion years ago (see: origin of life).

The notion that "all life [is] from [an] egg" (from the Latin "Omne vivum ex ovo") is a foundational concept of modern biology, it means that there has been an unbroken continuity of life from the initial origin of life to the present time. Up into the 19th century it was commonly believed that life forms can appear spontaneously under certain conditions (see abiogenesis). The universality of the genetic code is generally regarded by biologists as definitive evidence in favor of the theory of universal common descent (UCD) for all bacteria, archaea, and eukaryotes (see Three domain system).

Description

Biology is the science of life (from the Greek words bios = life and logos = reasoned account). It is concerned with the characteristics and behaviors of organisms, how species and individuals come into existence, and the interactions they have with each other and with their environment. Biology encompasses a broad spectrum of academic fields that are often viewed as independent disciplines. Together, they study life over a wide range of scales.

Life is studied at the atomic and molecular scale in molecular biology, biochemistry, and molecular genetics. At the level of the cell, it is studied in cell biology and at multicellular scales, it is examined in physiology, anatomy, and histology. Developmental biology studies life at the level of the development or ontogeny of an individual organism.

Moving up the scale towards more than one organism, genetics considers how heredity works between parent and offspring. Ethology considers group behavior of more than one individual. 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.

History of the word "biology"

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 (Hydrog�ologie, 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.

Related topics

Main articles: List of biology topics

Topics related to biology (Category)
People and history	Biologist - Notable biologists - History of biology - Nobel Prize in Physiology or Medicine - Timeline of biology and organic chemistry - List of geneticists and biochemists
Institutions, publications	NASA Ames Research Center - Bachelor of Science - Publications
Terms and phrases	Omne vivum ex ovo - In vivo - In vitro - In utero - In silico
Related disciplines	Medicine (Physician) - Physical anthropology
Outstanding problems	Origin of life - Unsolved problems in biology
Other	List of technologies - List of conservation topics
Biomedical topics	Lists of biomedical topics: | # | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

Further reading

• Lynn Margulis, Five Kingdoms: An Illustrated Guide to the Phyla of Life on Earth, 3rd ed., St. Martin's Press, 1997, paperback, ISBN 0805072527 (many other editions)
• Neil Campbell, Biology (7th edition), Benjamin-Cummings Publishing Company, 2004, hardcover, ISBN 080537146X