Biology (from
Greek βιολογία - βίος,
bios, "
life";
-λογία,
-logia, study of) is the
natural science concerned with the study of life and living
organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. The term
biology in its modern sense appears to have been introduced independently by
Karl Friedrich Burdach (1800),
Gottfried Reinhold Treviranus (
Biologie oder Philosophie der lebenden Natur, 1802), and
Jean-Baptiste Lamarck (
Hydrogéologie, 1802).
Biology is a vast subject containing many subdivisions, topics, and theories. Five unifying principles form the fundamental axioms of modern biology:
cell theory,
evolution,
gene theory,
energy, and
homeostasis.
These fields are further divided based on the scale at which organisms are studied and the methods used to study them:
biochemistry examines the rudimentary chemistry of life;
molecular biology studies the complex interactions of systems of biological molecules;
cellular biology examines the basic building block of all life, the
cell;
physiology examines the physical and chemical functions of the tissues,
organs, and organ systems of an organism; and
ecology examines how various organisms interrelate with their environment.
The classification, taxonomy, and nomenclature of biological organisms is administered by the
International Code of Zoological Nomenclature,
International Code of Botanical Nomenclature, and
International Code of Nomenclature of Bacteria for animals, plants, and bacteria, respectively. Viruses, viroids, prions, and all other sub-viral agents that demonstrate biological characteristics are controlled by the
International Code of Virus classification and nomenclature. However, several other viral classification systems do exist.
History
Although the modern for of biology has been introduced in relatively recent histroy, sciences related to and included within biology have been studied traditionally since ancient times. Natural philosophy has been independantly studied as early as the ancient civilizations such as
Mesopotamia,
Egypt, the
Indian subcontinent, and
China. However, the origins of modern biology and the approach to its examination and research are usually traced back to
ancient Greece. While traditional study of medicine date back to
Hippocrates, it was
Aristotle who contributed greatly to the development of biology. Especially important are his
History of Animals and other works where he showed naturalist leanings and later even more empirical works that focused on biological causation and the diversity of life. Aristotle's successor at the
Lyceum,
Theophrastus, wrote a series of books on
botany which survived as the most important contribution of antiquity to botany, even into the
Middle Ages.
Significant advances in the study and development of biology where promoted through the efforts of such
Muslim physicians as the
Afro-Arab scholar
al-Jahiz (781–869) in zoology, the
Kurdish biologist
Al-Dinawari (828–896) in botany,
[, in ] and the
Persian physician
Rhazes (865–925) in
anatomy and
physiology. These philosophers elaborated on, expanded, and improved the Greek biological theories and systematics. 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.
Biology began to quickly develop and grow with
Antony van Leeuwenhoek's dramatic improvement of the microscope. It was then that scholars discovered
spermatozoa,
bacteria,
infusoria and the sheer strangeness and diversity of microscopic life. Investigations by
Jan Swammerdam led to new interest in
entomology and built the basic techniques of microscopic dissection and
staining.
Advances in
microscopy also had a profound impact on biological thinking itself. In the early 19th century, a number of biologists pointed to the central importance of the
cell. In 1838 and 1839,
Schleiden and
Schwann began promoting the ideas that (1) the basic unit of organisms is the cell and (2) that individual cells have all the characteristics of
life, though they opposed the idea that (3) all cells come from the division of other cells. Thanks to the work of
Robert Remak and
Rudolf Virchow, however, by the 1860s most biologists accepted all three tenets of what came to be known as
cell theory.
Meanwhile, taxonomy and classification began to present a focal point in the study of natural history.
Carolus Linnaeus published a basic
taxonomy for the natural world in 1735 (variations of which have been in use ever since), and in the 1750s introduced
scientific names for all his species.
Georges-Louis Leclerc, Comte de Buffon, treated species as artificial categories and living forms as malleable—even suggesting the possibility of
common descent. Though he was opposed to evolution, Buffon is a key figure in the
history of evolutionary thought; his work would influence the evolutionary theories of both
Lamarck and
Darwin.
Serious evolutionary thinking originated with the works of
Jean-Baptiste Lamarck. However, it was the British naturalist
Charles Darwin, combining the biogeographical approach of Humboldt, the uniformitarian geology of Lyell,
Thomas Malthus's writings on population growth, and his own morphological expertise, that created a more successful evolutionary theory based on
natural selection; similar evidence led
Alfred Russel Wallace to independently reach the same conclusions.
The discovery of the physical representation of heredity came along with evoluttionary principles and
population genetics. In the 1940s and early 1950s, experiments pointed to
DNA as the portion of
chromosomes (and perhaps other nucleoproteins) that held genes. A focus on new model organisms such as
viruses and
bacteria, along with the discovery of the double helical structure of DNA in 1953, marked the transition to the era of
molecular genetics.
Foundations of modern biology
There are five unifying principles of biology:
Cell theory
Cell theory states that:
- The cell is the fundamental unit of life
- All living things are composed of one or more cells or the secreted products of those cells, such as shells
- The cell is considered to be the basic part of the pathological processes of an organism
Evolution
thumb|right|300px|Natural selection of a population for dark coloration.
A central organizing concept in biology is that life changes and develops through
evolution, and that all life-forms known have a
common origin. Introduced into the scientific lexicon by
Jean-Baptiste de Lamarck in 1809,
established evolution fifty years later as a viable theory by articulating its driving force:
natural selection. (
Alfred Russel Wallace is recognized as the co-discoverer of this concept as he helped research and experiment with the concept of evolution).
Darwin theorized that species and breeds developed through the processes of
natural selection and
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 known as 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,
spontaneous generation, the belief that life forms could appear spontaneously under certain conditions, was widely supported. This misconception was challenged by
William Harvey. Although his work predated the microscope, he was led to suggest that life came from invisible 'eggs.' In the frontispiece of his book
Exercitationes de Generatione Animalium (
Essays on the Generation of Animals), he made an expression of
biogenesis: "Omnia ex ovo" (everything from eggs).
Evolution is now used to explain the great variations of life found on Earth.
A group of organisms have 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 collective universality 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).
Evolution does not always give rise to progressively more complex organisms. For example, the process of
dysgenics has been reportedly observed among the human population.
Genetics
A Punnett square depicting a cross between two pea plants heterozygous for purple (B) and white (b) blossoms
s are the primary units of inheritance in all organisms. A
gene is a unit of
heredity and a region of
DNA that influences a particular characteristic in an organism. All organisms, from bacteria to animals, share the same basic machinery that copies and translates DNA into proteins. Cells
transcribe a DNA gene into an RNA version of the gene, and a
ribosome then
translates the RNA into a protein. Additionally, DNA codes for the same proteins regardless of what organism it is present in. A sequence of DNA that codes for insulin in humans will also code for insulin when inserted into other organisms, such as plants.
DNA usually occurs as linear
chromosomes in eukaryotes, and circular chromosomes in prokaryotes. The set of chromosomes in a cell is collectively known as its
genome. A chromosome is an organized structure consisting of
DNA and
histones. Genomic DNA is located in the
cell nucleus of eukaryotes, as well as small amounts in
mitochondria and
chloroplasts. In prokaryotes, the DNA is held within an irregularly shaped body in the cytoplasm called the
nucleoid. The genetic information in a genome is held within genes, and the complete set of this information in an organism is called its
genotype.
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
uni-cellular or
multi-cellular, exhibit homeostasis.
In order, to maintain dynamic equilibrium, a system must detect and respond to stimuli. After the detection of stimuli, a system will respond accordingly through at least one of the two forms of biological feedback:
negative feedback and
positive feedback.
[Marieb, Elaine N. & Hoehn, Katja (2007). Human Anatomy & Physiology (Seventh ed.). San Francisco, CA: Pearson Benjamin Cummings.] Negative feedback mechanism consists of reducing the output or activity of any organ or system back to its normal range of functioning. One example of negative feedback is the human body's release of
insulin when blood sugar levels are too high. Another example is the release of
glucagon when sugar levels are too low. Positive feedback mechanisms are designed to accelerate or enhance the output created by a stimulus that has already been activated. One example of a positive feedback event in the human body is blood platelet accumulation, which, in turn, causes blood clotting in response to a break or tear in the lining of blood vessels. Another example is the release of oxytocin to intensify the contractions that take place during childbirth.
[Marieb, Elaine N. & Hoehn, Katja (2007). Human Anatomy & Physiology (Seventh ed.). San Francisco, CA: Pearson Benjamin Cummings.]Energy
The survival of a living organism depends on the continuous input of
energy. 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. In this process,
molecules of
chemical substances that constitute
food play two roles; first, they contain energy that can be transformed for biological
chemical reactions; and also develop molecular structures made up of biomolecules.
Nearly all of the energy needed for life processes originates from the Sun,
which plants and other autotrophs convert into chemical energy (organic molecules) via
photosynthesis. A few
ecosystems, however, depend entirely on energy extracted from
methane,
sulfides, or other non-
luminal energy sources by
chemotrophs.
Some of the captured energy is used to produce
biomass to sustain
life and provide energy for its growth and development. The majority of the rest of this energy is lost as heat and waste molecules. The most common processes for converting the energy trapped in chemical substances into energy useful to sustain life are
metabolism and
cellular respiration.
Research
Structural
Schematic of typical animal
cell depicting the various
organelles and structures.
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.
[Hartl D, Jones E (2005)]
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 progressively 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
Danio rerio, the mouse
Mus musculus,, and the weed
Arabidopsis thaliana. A model organism is a
species that is extensively studied to understand particular biological
phenomena, with the expectation that discoveries made in the organism model will provide insight into the workings of other organisms.
Physiological
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 borrows techniques from both research 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
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 partly based on
paleontology, which uses the
fossil record to answer questions about the mode and tempo of evolution,
and partly on the developments in areas such as
population genetics and evolutionary theory. In the 1980s,
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.
Taxonomy
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:
However, many scientists now consider this five-kingdom system outdated. Modern alternative classification systems generally begin with the
three-domain system:
- Archaea (originally Archaebacteria)
These domains reflect whether the cells have nuclei or not, as well as differences in the cell exteriors.
Further, each kingdom is broken down recursively until each species is separately classified. The order is:
There is also a series of intracellular
parasites that are "on the edge of life" in terms of
metabolic activity, meaning that many scientists do not actually classify these structures as alive, due to their lack of at least one or more of the fundamental functions by which life is defined. They are classified as:
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. Additionally, the entire term would be italicized or underlined.
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 merging 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 BioCode draft has received little attention since 1997; its originally planned implementation date of January 1, 2000, has passed unnoticed. However, a 2004 paper concerning the
cyanobacteria does advocate a future adoption of a BioCode and interim steps consisting of reducing the differences between the codes.
The
International Code of Virus Classification and Nomenclature (ICVCN) remains outside the BioCode.
Ecology
Ecology studies the distribution and abundance of
living organisms, and the interactions between organisms and their
environment. The
habitat of an organism can be described as the local abiotic factors such as
climate and
ecology, plus the other organisms and biotic factors that share its environment.
Ecological systems are studied at several different levels, from individuals and
populations to
ecosystems and the
biosphere. The term
population biology is often used interchangeably with
population ecology, although population biology is more frequently used when studying
diseases,
viruses, and
microbes, while population ecology is more commonly when studying plants and animals. As can be surmised, ecology is a science that draws on several disciplines.
Ethology studies animal
behavior (particularly that 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.
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
savanna.
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 within the province of ecology.
Branches of Biology
These are the main branches of biology:
- Agriculture - study of producing crops from the land, with an emphasis on practical applications
- Anatomy - the study of form and function, in plants, animals, and other organisms, or specifically in humans
- Biochemistry - the study of the chemical reactions required for life to exist and function, usually a focus on the cellular level
- Bioengineering - the study of biology through the means of engineering with an emphasis on applied knowledge and especially related to biotechnology.
- Bioinformatics - also classified as a branch of information technology (IT) it is the study, collection, and storage of genomic and other biological data
- Biomechanics - often considered a branch of medicine, the study of the mechanics of living beings, with an emphasis on applied use through artificial limbs, etc.
- Biomimetics - science of adapting designs from nature to solve modern problems.
- Biophysics - the study of biological processes through physics, by applying the theories and methods traditionally used in the physical sciences
- Biotechnology - a new and sometimes controversial branch of biology that studies the manipulation of living matter, including genetic modification
- Cell Biology - the study of the cell as a complete unit, and the molecular and chemical interactions that occur within a living cell.
- Conservation Biology - the study of the preservation, protection, or restoration of the natural environment, natural ecosystems, vegetation, and wildlife
- Cryobiology - the study of the effects of lower than normally preferred temperatures on living beings.
- Ecology - the study of the interactions of living organisms with one another and with the non-living elements of their environment.
- Environmental Biology - the study of the natural world, as a whole or in a particular area, especially as affected by human activity
- Epidemiology - a major component of public health research, it is the study of factors affecting the health and illness of populations
- Ethology - the study of animal behavior.
- Genetics - the study of genes and heredity.
- Histology - the study of cells and tissues, a microscopic branch of anatomy.
- Marine Biology - the study of ocean ecosystems, plants, animals, and other living beings.
- Microbiology - the study of microscopic organisms (microorganisms) and their interactions with other living things
- Molecular Biology - the study of biology and biological functions at the molecular level, some cross over with biochemistry
- Neurobiology - the study of the nervous system, including anatomy, physiology, even pathology
- Oceanography - the study of the ocean, including ocean life, environment, geography, weather, and other aspects influencing the ocean.
- Population ecology - the study of populations of organisms, including how they increase and go extinct
- Paleontology - the study of fossils and sometimes geographic evidence of prehistoric life
- Pharmacology - the study and practical application of preparation, use, and effects of drugs and synthetic medicines.
- Physiology - the study of the functioning of living organisms and the organs and parts of living organisms
- Phytopathology - the study of plant diseases (also called Plant Pathology)
- Virology - the study of viruses and some other virus-like agents
- Zoology - the study of animals, including classification, physiology, development, and behavior (See also Entomology, Ethology, Herpetology, Ichthyology, Mammology, and Ornithology)
See also
Notes and References
