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Biology is the natural science that involves the study of life and living organisms, including
their physical structure, chemical composition, function, development and evolution
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Despite the broad scope and the complexity of
the science, there are certain unifying concepts that consolidate it into a single, coherent field
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Living organisms are open
systems that survive by transforming energy and decreasing their local entropy[2] to maintain a stable
and vital condition defined as homeostasis
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Sub-disciplines of biology are defined by the scale at which life is studied, the kinds of organisms
studied, and the methods used to study them: biochemistry examines the rudimentary chemistry of
life; molecular biology studies the complex interactions among biological molecules; cellular
biology examines the basic building-block of all life, the cell; physiology examines the physical and
chemical functions of tissues, organs, and organ systems; ecology examines how organisms interact
in their environment; and evolutionary biology examines the processes that produced the diversity of
life
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1Cell theory
o 2
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3Genetics
o 2
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5Energy

o 3
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2Physiological
o 3
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4Systematic
o 3
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6Ecological and environmental
4Basic unresolved problems in biology
5Branches
6See also
7References
8Further reading
9External links

History
Main article: History of biology

A Diagram of a fly from Robert Hooke's innovative Micrographia, 1665

Ernst Haeckel's Tree of Life (1879)

The term biology is derived from the Greek word βίος, bios, "life" and the suffix -λογία, -logia, "study
of
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It was used again in 1766 in a
work entitled Philosophiae naturalis sive physicae: tomus III, continens geologian, biologian,
phytologian generalis, by Michael Christoph Hanov, a disciple of Christian Wolff
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In 1797, Theodor Georg August Roose
used the term in the preface of a book, Grundzüge der Lehre van der Lebenskraft
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The term came into its modern usage with the six-volume treatise Biologie,
oder Philosophie der lebenden Natur(1802–22) by Gottfried Reinhold Treviranus, who announced:[6]
The objects of our research will be the different forms and manifestations of life, the
conditions and laws under which these phenomena occur, and the causes through which
they have been effected
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Although modern biology is a relatively recent development, sciences related to and included
within it have been studied since ancient times
...
However, the
origins of modern biology and its approach to the study of nature are most often traced back
to ancient Greece
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460–
370 BC), it was Aristotle(384–322 BC) who contributed most extensively to the development of
biology
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Aristotle's successor at the Lyceum, Theophrastus, wrote a series of books
on botany that survived as the most important contribution of antiquity to the plant sciences,
even into the Middle Ages
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Medicine was especially well studied by Islamic scholars working in
Greek philosopher traditions, while natural history drew heavily on Aristotelian thought,
especially in upholding a fixed hierarchy of life
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It was then that scholars
discovered spermatozoa, bacteria, infusoria and the diversity of microscopic life
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[11]
Advances in microscopy also had a profound impact on biological thinking
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Then, in
1838, Schleiden and Schwann began promoting the now universal ideas that (1) the basic unit
of organisms is the cell and (2) that individual cells have all the characteristics of life, although
they opposed the idea that (3) all cells come from the division of other cells
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[12][13]
Meanwhile, taxonomy and classification became the focus of natural historians
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[14] Georges-Louis Leclerc, Comte de Buffon, treated species as artificial categories and
living forms as malleable—even suggesting the possibility of common descent
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[15]
Serious evolutionary thinking originated with the works of Jean-Baptiste Lamarck, who was the
first to present a coherent theory of evolution
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Lamarck believed that these acquired traits could then be passed on to the
animal's offspring, who would further develop and perfect them
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[18][19] Although it was the subject
of controversy (which continues to this day), Darwin's theory quickly spread through the scientific
community and soon became a central axiom of the rapidly developing science of biology
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In the 1940s and early 1950s, experiments pointed to DNA as the
component of chromosomes that held the trait-carrying units that had become known as genes
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From the 1950s to present times, biology has been vastly extended in
the molecular domain
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Holley and Marshall Warren Nirenberg after DNA was understood to contain codons
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This project was essentially completed in 2003,[20] with further analysis still
being published
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Foundations of modern biology
Cell theory

Human cancer cells with nuclei (specifically the DNA) stained blue
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The cell on the left is going through mitosis and its DNA
has condensed
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In multicellular
organisms, every cell in the organism's body derives ultimately from a single cell in a
fertilized egg
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[21] In addition, the phenomenon of energy flow occurs in cells in processes that are
part of the function known as metabolism
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Research into the origin of life, abiogenesis,
amounts to an attempt to discover the origin of the first cells
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Main article: Evolution
A central organizing concept in biology is that life changes and develops through evolution, and
that all life-forms known have a common origin
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This universal common ancestor of all organisms is believed to have
appeared about 3
...
[22] Biologists regard the ubiquity of the genetic code as
definitive evidence in favor of the theory of universal common descent for all bacteria, archaea,
and eukaryotes (see: origin of life)
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[25][26][27] (Alfred Russel Wallaceis recognized as the co-discoverer of this
concept as he helped research and experiment with the concept of evolution
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Darwin theorized that species flourish or die when subjected to the processes of natural
selection or selective breeding
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[30]
The evolutionary history of the species—which describes the characteristics of the various
species from which it descended—together with its genealogical relationship to every other
species is known as its phylogeny
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These include the comparisons of DNA sequences, a product of molecular
biology (more particularly genomics), and comparisons of fossils or other records of ancient
organisms, a product of paleontology
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(For a
summary of major events in the evolution of life as currently understood by biologists,
see evolutionary timeline
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But, those organizations can only be
understood in the light of how they came to be by way of the process of evolution
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[32]

Genetics

A Punnett square depicting a cross between two pea plants heterozygous for purple (B) and white (b)
blossoms

Main article: Genetics
Genes are the primary units of inheritance in all organisms
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All organisms, from bacteria to animals, share the same basic machinery that copies and
translates DNA into proteins
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The translation code from RNA codon to amino acid is the same for most organisms
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[33]
DNA is found as linear chromosomes in eukaryotes, and circular chromosomes in prokaryotes
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The set of
chromosomes in a cell and any other hereditary information found in
the mitochondria, chloroplasts, or other locations is collectively known as a cell's genome
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In prokaryotes, the DNA is held within an irregularly shaped
body in the cytoplasm called the nucleoid
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[35]

Homeostasis
Main article: Homeostasis

The hypothalamus secretes CRH, which directs the pituitary gland to secrete ACTH
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The GCs then reduce the rate of
secretion by the hypothalamus and the pituitary gland once a sufficient amount of GCs has been
released
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All living organisms, whether unicellular or multicellular,
exhibit homeostasis
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After the detection of a perturbation, a biological system normally
responds through negative feedback that stabilize conditions by reducing or increasing the
activity of an organ or system
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Basic overview of energy and human life
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Chemical reactions
that are responsible for its structure and function are tuned to extract energy from substances
that act as its food and transform them to help form new cells and sustain them
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The organisms responsible for the introduction of energy into an ecosystem are known as
producers or autotrophs
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[38] Plants and other phototrophs use solar energy via a process known as photosynthesis to
convert raw materials into organic molecules, such as ATP, whose bonds can be broken to
release energy
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[40]
Some of the energy thus captured produces biomass and energy that is available for growth and
development of other life forms
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The most important processes for converting the energy trapped in
chemical substances into energy useful to sustain life are metabolism[41] and cellular
respiration
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Molecular biology is the study of biology at the molecular level
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Molecular biology is a study of
the interactions of the various systems within a cell, including the interrelationships of DNA,
RNA, and protein synthesis and how those interactions are regulated
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This is
done on both the microscopicand molecular levels, for unicellular organisms such as bacteria,
as well as the specialized cells of multicellular organisms such as humans
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The similarities
and differences between cell types are particularly relevant to molecular biology
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[44]
Genetics is the science of genes, heredity, and the variation of organisms
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Genetics provides research tools used in the
investigation of the function of a particular gene, or the analysis of genetic interactions
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Developmental biology studies the process by which organisms grow and develop
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Model organismsfor developmental
biology include the round worm Caenorhabditis elegans,[47] the fruit fly Drosophila
melanogaster,[48] the zebrafish Danio rerio,[49] the mouse Mus musculus,[50] and the
weed Arabidopsis thaliana
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)[53]

Physiological
Main article: Physiology
Physiology is the study of the mechanical, physical, and biochemical processes of living
organisms function as a whole
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Physiological studies have traditionally been divided into plant physiology and animal
physiology, but some principles of physiology are universal, no matter what
particular organism is being studied
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The field of animal physiology extends the tools and
methods of human physiology to non-human species
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Physiology is the study the interaction of how, for example,
the nervous, immune, endocrine, respiratory, and circulatory systems, function and interact
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Evolutionary
Evolutionary research is concerned with the origin and descent of species, and their change
over time
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Evolutionary biology is partly based on paleontology, which uses the fossil record to answer
questions about the mode and tempo of evolution,[54] and partly on the developments in areas
such as population genetics
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[56] Phylogenetics, systematics, and taxonomy are related fields often
considered part of evolutionary biology
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Trees constructed
with other genes are generally similar, although they may place some early-branching groups very
differently, presumably owing to rapid rRNA evolution
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The hierarchy of biological classification's eight major taxonomic ranks
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This diagram uses a 3 Domains / 6 Kingdoms format

Main article: Systematics
Multiple speciation events create a tree structured system of relationships between species
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[57] However, systematics was an active field of research
long before evolutionary thinking was common
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[59] However, many scientists now consider
this five-kingdom system outdated
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[60]

Further, each kingdom is broken down recursively until each species is separately classified
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Outside of these categories, there are obligate intracellular parasites that are "on the edge of
life"[61] in terms of metabolicactivity, meaning that many scientists do not actually classify such
structures as alive, due to their lack of at least one or more of the fundamental functions or
characteristics that define life
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The scientific name of an organism is generated from its genus and species
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Homo is the genus, and sapiens the species
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[62] Additionally, the entire term may be italicized or underlined
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It includes ranks
and binomial nomenclature
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The classification of viruses, viroids, prions, and all other subviral agents that demonstrate biological characteristics is conducted by the International
Committee on Taxonomy of Viruses (ICTV) and is known as the International Code of Viral
Classification and Nomenclature (ICVCN)
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A merging draft, BioCode, was published in 1997 in an attempt to standardize nomenclature in
these three areas, but has yet to be formally adopted
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A revised BioCode that, instead of replacing the existing codes, would provide a
unified context for them, was proposed in 2011
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The ICVCN remains outside the
BioCode, which does not include viral classification

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