Encyclopedia
Biology 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
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 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 mass.
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 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 , changes in living organisms over time ,
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 groups of organisms. 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 , which examines the possibility of life beyond the Earth.
Principles of biology
Unlike
physics, biology does not usually describe systems in terms of objects which obey immutable physical laws described by
mathematics. Biological systems are not completely random, however, as they may 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. Nevertheless, the biological sciences are characterized and unified by several major underlying principles and concepts: universality,
evolution, diversity,
continuity, genetics,
homeostasis, and interactions.
However, biology is still considered to be subject to the same physical laws that other branches of science obey, such as the laws of thermodynamics and conservation of mass.
Universality: Biochemistry, cells, and the genetic code
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 are made of cells. Similarly, all organisms share common developmental processes. For example, in most animals, the basic stages of early
embryonic development share similar morphological characteristics and include similar
genes.
Evolution: The central principle of biology
The central organizing concept in biology is that all life has a common origin and has changed and developed through the process of
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 . 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 .
Diversity: The variety of living organisms
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 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 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 -- Bacteria -- Eukaryota
| style = "background: pink; padding: 4px;" | Animal [i]ia - Animals
...
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 -- Viroid
Avsunviroidae [i] ...
s --
Prions
Continuity: The common descent of life
Up into the
19th century, it was commonly believed that life forms could appear spontaneously under certain conditions . This misconception was challenged by
William Harvey's diction that "all life [is] from [an] egg" , 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 for all
bacteria,
archaea, and
eukaryotes .
Homeostasis: Adapting to change
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 ; 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: Groups and environments
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 of biology
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 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 is a free-living nematode [i] , about 1 mm [i] in length, wh ...
, the fruit fly
Drosophila melanogaster is a two-winged insect that belongs to the Diptera [i], the order [i] ...
, the zebrafish
Brachydanio rerio, the mouse
Mus musculus is the
common house mouse....
, and the weed
Arabidopsis thaliana, commonly called arabidopsis,
thale cress, or
mouse-ear cress, a sm...
.
Physiology of organisms
Main articles: Physiology,
AnatomyPhysiology 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
Main articles: Evolutionary biology,
Biodiversity,
Botany,
ZoologyEvolutionary 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.
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 , the International Code of Zoological Nomenclature , and the International Code of Nomenclature of Bacteria . 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 remains outside the BioCode.
Interactions of organisms
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 , 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.
History of the word "biology"
Formed by combining the Greek
', meaning 'life', and ', meaning 'study of', the word "biology" in its modern sense seems to have been introduced independently by
Gottfried Reinhold Treviranus and by
Jean-Baptiste Lamarck . 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:
External links
- : Daily updated biology news & community website.
- : Major biology forum, dictionary and collection of tutorials and articles.
- : Research News and Articles from Biological Science and related fields.
- : A proposal for organism naming.
-
- PhyloCode, http://www.ohiou.edu/phylocode/index.html
- : A multi-authored, distributed Internet project containing information about phylogeny and biodiversity.
- Bioscience research journals.
- Protocols, graduate school information, hard to find definitions.
Journal Links- A peer-reviewed, open-access journal published by the Public Library of Science
- A biological journal publishes peer-reviewed scientific papers of significance
See also
Topics related to biology
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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 is the third and final studio album from the American [i] grunge [i] ...
- In silico | Related disciplines | Medicine - Physical anthropology - Environmental science - Life Sciences - Biotechnology | Outstanding problems | Origin of life - Unsolved problems in biology | Other | List of technologies - List of conservation topics |
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 0-8050-7252-7
- Neil Campbell, Biology , Benjamin-Cummings Publishing Company, 2004, hardcover, ISBN 0-8053-7146-X
- Johnson George B. 2005 "Biology, Visualizing Life." Holt, Rinehart, and Winston. ISBN 0-03-016723-X
