Biology (from Greek βιολογία - βίος, bios, "life"; -λογία, -logia, study of) is the science that studies living organisms. Prior to the nineteenth century, biology came under the general study of all natural objects called natural history. The term biology was first coined by Gottfried Reinhold Treviranus.[citation needed] It 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]
Biology examines the structure, function, growth, origin, evolution, distribution and classification of all living things. Five unifying principles form the foundation of modern biology: cell theory, evolution, gene theory, energy, and homeostasis.[2]
Traditionally, the specialized disciplines of biology 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. These fields 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, 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 with their environment.
Foundations of modern biology
There are five unifying principles of biology[2]:
- Cell theory. All living organisms are made of one or more cells, the basic living unit of function in organisms. All cells come 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.
- Genes. A living organism's traits are encoded in DNA. Segments of DNA that, taken as a whole, specify a trait are known as genes. In addition, traits are passed on from one generation to the next by way of these genes. All information transfers from the genotype, the unobservable genetic traits, 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.
- Energy. The attribute of any living organism that is essential for its state. (e.g. required for metabolism)
Cell theory
Cell theory states that[3]:
- 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.
- Cells arise from other cells through cell division
- In multicellular organisms, every cell in the organism's body is produced from a single cell in a fertilized egg.
- The cell is considered to be the basic part of the pathological processes of an organism.
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. Introduced into the scientific lexicon by Jean-Baptiste de Lamarck in 1809, Charles Darwin 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.[4] 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, spontaneous generation, the belief that life forms could appear spontaneously under certain conditions, was widely believed. 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 means that there is an unbroken continuity of life from its initial origin to the present time.
A group of organisms share 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.[5] 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 (see: origin of life)[6].
Evolution does not always give rise to progressively more complex organisms. For example, the process of dysgenics has been observed among the human population.[7]
Genetics
Genes are the primary units of inheritance in all organisms and are made of DNA. Widely different organisms, including bacteria, plants, animals, and fungi, share the same basic machinery that copies and transcribes DNA into proteins. For example, bacteria with inserted human DNA may, under the right circumstances, manufacture a human protein.
All the genes in an organism or cell are together known as the genome, which–in eukaryotes but not bacteria–is stored on one or more chromosomes. A chromosome is an organized structure consisting of DNA and protein. Cells transcribe a DNA gene into an RNA version of the gene, and a ribosome then translates the RNA into a protein.
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 roots of plants help prevent soil from eroding, which helps to maintain the ecosystem. Tissues and organs can also maintain homeostasis. It is also the maintenance of stability of numbers of individuals within a population.
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 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 in the presence of water and minerals. A few ecosystems, however, depend entirely on energy extracted from methane, sulfides, or other inorganic molecules by chemosynthetic microorganisms. Some of the captured energy is used to produce biomass to sustain life and provide energy for its growth and development. A part of this energy is lost as heat and waste molecules. The common processes for converting energy in chemical substances into energy useful to sustain life are metabolism[8] and respiration.
Research
Structural
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
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
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 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.
[edit] 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:[9]
However, many scientists now consider this five-kingdom system to be outdated. Modern alternative classification systems generally begin with the three-domain system:[10]
- Archaea (originally Archaebacteria)
- Bacteria (originally Eubacteria)
- Eukarya (including protists, fungi, plants, and 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:
There is also a series of intracellular parasites that are progressively "less alive" in terms of metabolic activity:
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 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.
Ecology
Ecology studies the distribution and abundance of living organisms, and the interactions between organisms and their environment.[11] 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, and the other organisms that share its habitat. 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.
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 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 the province of ecology.
Branches of Biology
These are the branches of biology:[12]
- 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
- Astrobiology- the study of evolution, distribution, and future of life in the universe. Also known as exobiology, exopaleontology, and bioastronomy.
- 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
- Biomathematics or Mathematical Biology - the study of biological processes through mathematics, with an emphasis on modeling.
- 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.
- Biomedical research - the study of the human body in health and disease
- 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
- Botany - the study of plants
- 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.
- Developmental Biology - (Embryology) the study of the processes through which an organism develops, from zygote to full structure.
- Ecology - the study of the interactions of living organisms with one another and with the non-living elements of their environment.
- Entomology - the study of insects
- 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.
- Evolution or Evolutionary Biology - the study of the origin and decent of species over time
- Genetics - the study of genes and heredity.
- Herpetology - the study of reptiles and amphibians
- Histology - the study of cells and tissues, a microscopic branch of anatomy.
- Ichthyology - the study of fish
- Integrative biology - the study of whole organisms
- Mammalogy - the study of mammals
- 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
- Mycology - the study of fungi
- 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.
- Ornithology - the study of birds
- Population ecology - the study of populations of organisms, including how they increase and go extinct
- Population genetics - the study of changes in gene frequencies in populations of organisms
- Paleontology - the study of fossils and sometimes geographic evidence of prehistoric life
- Pathobiology or pathology - the study of diseases, and the causes, processes, nature, and development of disease
- Parasitology - the study of parasites and parasitism
- 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
- Conservation biology
- List of biological websites
- List of biologists
- List of biology topics
- Periodic Table of Life Sciences in Tinbergen's four questions
