ژواکپېژندنه

From Wikipedia

ژواکپېژندنه Portal

ژواکپېژندنه دا هغه پوهه يا علم دی چې د ژوند په اړه څرخي.او د ژوند سره تړاو لري. دا د ژوؤ يا ژوندي غړو (اورګانزمو) په اړه او د هغو د خاصيت ،او توپيريزو ساينسي اړخونو باندې پنځونې يا بحسونه کوي . is  the branch of science dealing with the study of life. 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 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 biochemistry to ecology.

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

At the organism level, biology has explained phenomena such as birth, growth, ageing, death and  decay of living organisms, similarities between the offsprings and  parents (heredity) and  flowering of plants have  puzzled humanity ever since antiquity. 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 through ages (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 to study human beings. However, at the molecular scale, life is  studied in the disciplines of molecular biology, biochemistry, and  molecular genetics. At the next 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 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 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.

[سمادول] د ژواکپېژندنې يا بيالوژي بنسټونه

Unlike physics, biology does not usually describe systems in terms of objects which obey immutable physical laws described by mathematics. Nevertheless, the biological sciences are  characterized and  unified by several major underlying principles and  concepts: universality, evolution, diversity, continuity, genetics, homeostasis, and  interactions.

[ and  the genetic code">سمادول] Universality: Biochemistry, cells, and  the genetic code

Schematic representation of DNA, the primary genetic material.

Main article: Life

The most salient example of biological universality is  that all living things share a common carbon-based biochemistry and  in particular pass on their characteristics via genetic material, which is  based on nucleic acids such as DNA and  which uses a common genetic code with only minor variations.

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. For example, in most metazoan organisms, the basic stages of early embryonic development share similar morphological characteristics and  include similar genes.

[سمادول] Evolution: The central principle of biology

Main article: 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 Russell 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).

[سمادول] Diversity: The variety of living organisms

 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."> 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." width="340" height="232" longdesc="../../../p/h/y/Image%7EPhylogeneticTree.png_bdea.html" class="thumbimage" />

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 its underlying unity, life exhibits an  astonishingly wide diversity in morphology, behavior, and  life histories. In order to grapple with this diversity, biologists attempt to classify all living things. Scientific classification seeks to reflect the evolutionary trees (phylogenetic trees) of the organism being classified. 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 clasification 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  all of the species is  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

[سمادول] Continuity: The common descent of life

Main article: Common descent

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 is  said to share 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 favor of the theory of universal common descent (UCD) for all bacteria, archaea, and  eukaryotes (see: origin of life).

[سمادول] Homeostasis: Adapting to change

Main article: 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.

[ and  environments">سمادول] Interactions: Groups and  environments

 and  in turn the stinging tentacles of the anemone protects the clown fish from its predators"> and  in turn the stinging tentacles of the anemone protects the clown fish from its predators" width="250" height="188" longdesc="../../../c/o/m/Image%7ECommon_clownfish.jpg_c597.html" class="thumbimage" />

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.

[سمادول] Scope of biology

Main article: List of biology disciplines

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.

[سمادول] Structure of life

 and  structures"> and  structures" width="300" height="201" longdesc="../../../b/i/o/Image%7EBiological_cell.png_5f5b.html" class="thumbimage" />

Schematic of typical animal cell depicting the various organelles and  structures

Main articles: Molecular biology, Cell biology, Genetics, Developmental biology

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.

[سمادول] 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.

[ and  evolution of organisms">سمادول] Diversity and  evolution 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"> 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" width="300" height="148" longdesc="../../../f/i/t/Image%7EFitness-landscape-cartoon.png_e411.html" class="thumbimage" />

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 behavioral ecology and  other fields.

[سمادول] 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 International Code of Virus Classification and  Nomenclature (ICVCN) remains outside the BioCode.

[سمادول] Interactions of organisms

 an  ecosystem."> an  ecosystem." width="319" height="170" longdesc="../../../f/o/o/Image%7EFoodweb.png_9f84.html" class="thumbimage" />

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

Main articles: Ecology, Ethology, Behavior, 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 behavior (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 behavior 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.

[سمادول] 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 (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.

[سمادول] تاريخ

Main articles: History of biology, History of medicine, History of genetics

Major discoveries in biology include:

• Cell theory
• Germ theory of disease
• Genetics
• Evolution
• DNA

[سمادول] See also

Main articles: List of biology topics

[سمادول] باندنۍ تړنې

Template:Wikibooks Template:Wikibookspar

• Biology News Net: Daily updated biology news & community website.
• BioNews :Latest Biology News : Research News and  Articles from Biological Science and  related fields.
• BioCode: A proposal for organism naming.
• NCBI Open-Access Books
• PhyloCode, [1]
• The Tree of Life: A multi-authored, distributed Internet project containing information about phylogeny and  biodiversity.
• BioOne Bioscience research journals.
• EverythingBio Protocols, graduate school information, hard to find definitions.

Journal Links

• PLos Biology A peer-reviewed, open-access journal published by the Public Library of Science
• Perspectives in Biology and  Medicine

[سمادول] 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

Template:Natural sciences-footer