(Redirected from Life science)
 ''Escherichia coli'' |  Tree fern |
 Goliath beetle |  Gazelle |
Biology studies the variety of life ''(clockwise from top-left)'' ''
E. coli'', tree
fern,
gazelle,
Goliath beetle
'Biology' (from Greek: βίος, ''bio'', "
life"; and λόγος, ''logos'', "
knowledge"), also referred to as the 'biological sciences', is the study of
living organisms utilizing the
scientific method. Biology examines the structure, function, growth, origin, evolution, and distribution of living things. It classifies and describes organisms, their function, how species come into existence, and the interactions they have with each other and with the
natural environment.
Most biological sciences are specialized disciplines. Traditionally, they are grouped by the type of organism being studied:
★
botany, the study of plants;
★
zoology, the study of animals, and
★
microbiology, the study of microorganisms.
The fields within biology are further divided based on the scale at which organisms are studied and the methods used to study them:
★
biochemistry examines the fundamental chemistry of life;
★
molecular biology studies the complex interactions of systems of biological molecules
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cellular biology examines the basic building block of all life, the
cell;
★
physiology examines the physical and chemical functions of the tissues and organ systems of an organism; and
★
ecology examines how various organisms interrelate.
Applied fields of biology such as
medicine and genetic research involve many specialized sub-disciplines.
Biology as a separate
science was developed in the nineteenth century, as scientists discovered that organisms shared fundamental characteristics. Biology is now a standard subject of instruction at schools and universities around the world, and over a million papers are published annually in a wide array of biology and medicine
journals.
[1]
Foundations of modern biology
There are four unifying principles of biology:
★
Cell theory. All living organisms are made of at least one cell, the basic unit of function in all organisms. In addition, the core mechanisms and chemistry of all cells in all organisms are similar, and cells emerge only from preexisting cells that multiply through cell division.
★
Evolution. Through
natural selection and
genetic drift, a population's inherited traits change from generation to generation.
★
Gene theory. A living organism's traits are encoded in their
DNA, the fundamental component of genes. In addition, traits are passed on from one generation to the next by way of these genes. All information flows from genes to the
phenotype, the observable physical or biochemical characteristics of the organism. Although the phenotype expressed by the gene may adapt to the environment of the organism, that information is not transferred back to the genes. Only through the process of evolution do genes change in response to the environment.
★
Homeostasis. The physiological processes that allow an organism to maintain its internal environment notwithstanding its external environment.
Cell theory
Main articles: Cell theory
The cell is the fundamental unit of life. Cell theory states that all living things are composed of one or more cells, or the
secreted products of those cells, for example,
shell and
bone. Cells arise from other cells through
cell division, and in multicellular organisms, every cell in the organism's body is produced from a single cell in a fertilized egg. Furthermore, the cell is considered to be the basic part of the pathological processes of an organism.
[2]
Evolution
Main articles: Evolution
A central organizing concept in biology is that all life has a common origin (see
Common descent) and has changed and developed through
evolution. 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). Darwin theorized that species and breeds developed through the processes of
natural selection as well as by
artificial selection or
selective breeding.
Genetic drift was embraced as an additional mechanism of evolutionary development in the
modern synthesis of the theory.
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 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. For a summary of major events in the evolution of life as currently understood by biologists, see
evolutionary timeline.
Up into the
19th century, it was commonly believed that life forms could appear spontaneously under certain conditions (see
spontaneous generation). 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 both living and extinct have been or 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).
Evolution does not always give rise to progressively more complex organisms. For example, the process of
dysgenics has been observed among the human population.
[3]
Gene theory
Main articles: Gene
Biological form and function is created from and is passed on to the next generation by genes, which are the primary units of inheritance. Physiological adaption to an organism's environment cannot be coded into its genes and cannot be inherited by its offspring (see
Lamarckism). Remarkably, widely different organisms, including bacteria, plants, animals, and fungi, all share the same basic machinery that copies and transcribes DNA into proteins. For example, bacteria with inserted human DNA will correctly yield the corresponding human protein.
The total complement of genes in an organism or cell is known as its
genome which is stored on one or more
chromosomes. A chromosome is a single, long DNA strand on which thousands of genes, depending on the organism, are encoded. When a gene is active, the DNA code is
transcribed into an RNA copy of the gene's information. A
ribosome then
translates the RNA into a structural
protein or
catalytic protein.
Homeostasis
Main articles: 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 exists at the cellular level, for example cells maintain a stable internal acidity (
pH); and at the level of the organism, for example
warm-blooded animals maintain a constant internal body temperature. Homeostasis is a term that is also used in association with
ecosystems, for example, the atmospheric concentration of
carbon dioxide on Earth has been regulated by the concentration of plant life on Earth because
plants remove more
carbon dioxide from the atmosphere during the daylight hours than they emit to the atmosphere at night.
Tissues and
organs can also maintain homeostasis.
Research
Main articles: List of biology disciplines
Structural
Schematic of typical animal
cell depicting the various
organelles and structures.
,
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.
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. 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.
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''.
Physiological
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.
Evolution
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.
,
Evolution,
Evolutionary synthesis,
Natural selection
Evolution 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,
botany, 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.
Up into the
19th century, it was believed that life forms were being continuously created under certain conditions (see
spontaneous generation). 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 favor of the theory of universal common descent (UCD) for all
bacteria,
archaea, and
eukaryotes (see:
origin of life).
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.
Taxonomy
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:
[4]
:
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:
[5]
:
Archaea (originally Archaebacteria) --
Bacteria (originally Eubacteria) --
Eukarya
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:
#
Domain
#
Kingdom
#
Phylum
#
Class
#
Order
#
Family
#
Genus
#
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 or underlined. 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
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.
Environmental
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
ecology, 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 Man and Animals" 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.
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.
History
Main articles: History of biology,
History of medicine
Although the concept of ''
biology'' as a single coherent field arose in the 19th century, the biological sciences emerged from
traditions of medicine and
natural history reaching back to
Galen and
Aristotle in ancient Greece. During the Renaissance and early modern period, biological thought was revolutionized by a renewed interest in
empiricism and the discovery of many novel organisms. Prominent in this movement were
Vesalius and
Harvey, who used experimentation and careful observation in physiology, and naturalists such as
Linnaeus and
Buffon who began to
classify the diversity of life and the
fossil record, as well as the development and behavior of organisms.
Microscopy revealed the previously unknown world of microorganisms, laying the groundwork for
cell theory. The growing importance of
natural theology, partly a response to the rise of
mechanical philosophy, encouraged the growth of natural history.
[ The Growth of Biological Thought, Mayr, E, , , Belknap Press, , ][6]
Over the 18th and 19th centuries, biological sciences such as
botany and
zoology became increasingly professional
scientific disciplines.
Lavoisier and other physical scientists began to connect the animate and inanimate worlds through physics and chemistry. Explorer-naturalists such as
Alexander von Humboldt investigated the interaction between organisms and their environment, and the ways this relationship depends on geography—laying the foundations for
biogeography,
ecology and
ethology. Naturalists began to reject
essentialism and consider the importance of
extinction and the
mutability of species.
Cell theory provided a new perspective on the fundamental basis of life. These developments, as well as the results from
embryology and
paleontology, were synthesized in s theory of
evolution by
natural selection. The end of the 19th century saw the fall of
spontaneous generation and the rise of the
germ theory of disease, though the mechanism of
inheritance remained a mystery.
[7][8]
In the early 20th century, the rediscovery of
Mendel's work led to the rapid development of
genetics by
Thomas Hunt Morgan and his students, and by the 1930s the combination of
population genetics and natural selection in the "
neo-Darwinian synthesis". New disciplines developed rapidly, especially after
Watson and
Crick proposed the structure of
DNA. Following the establishment of the
Central Dogma and the cracking of the
genetic code, biology was largely split between ''organismal biology''—the fields that deal with whole organisms and groups of organisms—and the fields related to ''
cellular and
molecular biology''. By the late 20th century, new fields like
genomics and
proteomics were reversing this trend, with organismal biologists using molecular techniques, and molecular and cell biologists investigating the interplay between genes and the environment, as well as the genetics of natural populations of organisms.
[9][10][11][12]
See also
: ''Main lists:
List of biology topics,
List of basic biology topics and
List of biologists''
References
1. Biology: A Functional Approach, King, TJ & Roberts, MBV, , , Thomas Nelson and Sons, ,
2. A unifying concept: the history of cell theory, Mazzarello, P, , , Nature Cell Biology,
3. New evidence of dysgenic fertility for intelligence in the United States, , Richard, Lynn, Intelligence,
4. Five Kingdoms: An Illustrated Guide to the Phyla of Life on Earth, , L, Margulis, WH Freeman & Co, 1997,
5. Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eukarya., Woese C, Kandler O, Wheelis M, , , Proc Natl Acad Sci U S A, 1990
6. A History of the Life Sciences, Magner, LN, , , TF-CRC, ,
7. Evolution, Futuyma, DJ, , , Sinauer Associates, ,
8. Biology in the Nineteenth Century: Problems of Form, Function and Transformation, Coleman, W, , , Cambridge University Press, ,
9. Life Science in the Twentieth Century, Allen, GE, , , Cambridge University Press, ,
10. Proteins, Enzymes, Genes: The Interplay of Chemistry and Biology, Fruton, JS, , , Yale University Press, ,
11. A History of Molecular Biology, Morange, M & Cobb, M, , , Harvard University Press, ,
12. Unifying Biology, Smocovitis, VB, , , Princeton University Press, ,
Further reading
★
Molecular Biology of the Cell, , Bruce, Alberts, Garland, 2002,
★
Ecology: From Individuals to Ecosystems, , Michael, Begon, Blackwell Publishing Limited, 2005,
★
Biology, , Neil, Campbell, Benjamin-Cummings Publishing Company, 2004,
★
Why Big Fierce Animals are Rare: An Ecologist's Perspective, , Paul, Colinvaux, Princeton University Press, 1979,
★
The Way Life Works, , Mahlon, Hoagland, Jones and Bartlett Publishers inc, 2001,
★
On Becoming a Biologist, , John Jr., Janovy, Bison Books, 2004,
★
Biology, Visualizing Life, , George B., Johnson, Holt, Rinehart, and Winston, 2005,
External links
★
The Dolan DNA Learning Center: The source for timely information about your life
★
OSU's Phylocode
★
''The Tree of Life'': A multi-authored, distributed Internet project containing information about phylogeny and biodiversity.
★
MIT video lecture series on biology
★
A wiki site for protocol sharing run from MIT.
★
Biology and Bioethics.
★
Biology online wiki dictionary.
★
Biology Video Sharing Community.
Journal links
★
PLos Biology A peer-reviewed, open-access journal published by the Public Library of Science
★
International Journal of Biological Sciences A biological journal publishes peer-reviewed scientific papers of significance
★
Perspectives in Biology and Medicine
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