. Biology is the that studies and living, including their, and. Despite the complexity of the science, there are certain unifying concepts that consolidate it into a single, coherent field. Biology recognizes the as the basic unit of life, as the basic unit of, and as the engine that propels the and of. Are that survive by transforming and decreasing their local to maintain a stable and vital condition defined as. Sub-disciplines of biology are defined by the research methods employed and the kind of system studied: uses mathematical methods to formulate quantitative models while performs empirical experiments to test the validity of proposed theories and understand the mechanisms underlying life and how it and from non-living matter about 4 billion years ago through a gradual increase in the complexity of the system. Main article: Cell theory states that the is the fundamental unit of, that all living things are composed of one or more cells, and that all cells arise from other cells through.
In, every cell in the organism's body derives ultimately from a single cell in a fertilized. The cell is also considered to be the basic unit in many pathological processes. In addition, the phenomenon of occurs in cells in processes that are part of the function known as.
Finally, cells contain hereditary information , which is passed from cell to cell during cell division. Research into the origin of life, amounts to an attempt to discover the origin of the first cells. Main article: A central organizing concept in biology is that life changes and develops through evolution, and that all life-forms known have a. The theory of evolution postulates that all on the, both living and extinct, have descended from a common ancestor or an ancestral. This is believed to have appeared about.
Biologists regard the ubiquity of the as definitive evidence in favor of the theory of universal common descent for all, and (see: ). The term 'evolution' was introduced into the scientific lexicon by in 1809, and fifty years later posited a scientific model of natural selection as evolution's driving force.
( is recognized as the co-discoverer of this concept as he helped research and experiment with the concept of evolution.) Evolution is now used to explain the great variations of life found on Earth. Darwin theorized that species flourish or die when subjected to the processes of. Was embraced as an additional mechanism of evolutionary development in the of the theory. The evolutionary history of the —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. Widely varied approaches to biology generate information about phylogeny.
These include the comparisons of, a product of (more particularly ), and comparisons of or other records of ancient organisms, a product of. Biologists organize and analyze evolutionary relationships through various methods, including, and.
(For a summary of major events in the evolution of life as currently understood by biologists, see.) Evolution is relevant to the understanding of the natural history of life forms and to the understanding of the organization of current life forms. But, those organizations can only be understood in the light of how they came to be by way of the process of evolution. Consequently, evolution is central to all fields of biology. Main article: are the primary units of inheritance in all organisms. A gene is a unit of and corresponds to a region of that influences the form or function of an organism in specific ways. All organisms, from bacteria to animals, share the same basic machinery that copies and translates DNA into.
Cells a DNA gene into an version of the gene, and a then the RNA into a sequence of known as a protein. The from RNA codon to amino acid is the same for most organisms. For example, a sequence of DNA that codes for in humans also codes for insulin when inserted into other organisms, such as plants. DNA is found as linear in, and circular chromosomes in. A chromosome is an organized structure consisting of and.
The set of chromosomes in a cell and any other hereditary information found in the, or other locations is collectively known as a cell's. In eukaryotes, genomic DNA is localized in the, or with small amounts in and. In prokaryotes, the DNA is held within an irregularly shaped body in the cytoplasm called the.
The genetic information in a genome is held within genes, and the complete assemblage of this information in an organism is called its. The secretes, which directs the to secrete. In turn, ACTH directs the adrenal cortex to secrete, such as. The GCs then reduce the rate of secretion by the hypothalamus and the pituitary gland once a sufficient amount of GCs has been released. Homeostasis is the ability of an to regulate its internal environment to maintain stable conditions by means of multiple adjustments that are controlled by interrelated regulation mechanisms.
All living, whether or, exhibit homeostasis. To maintain dynamic equilibrium and effectively carry out certain functions, a system must detect and respond to perturbations. After the detection of a perturbation, a biological system normally responds through that stabilize conditions by reducing or increasing the activity of an organ or system. One example is the release of when sugar levels are too low.
Basic overview of. Energy The survival of a living organism depends on the continuous input of. Chemical reactions that are responsible for its structure and function are tuned to extract from substances that act as its food and transform them to help form new cells and sustain them. In this process, of that constitute play two roles; first, they contain energy that can be transformed and reused in that organism's biological,; second, food can be transformed into new molecular structures (biomolecules) that are of use to that organism. The organisms responsible for the introduction of energy into an ecosystem are known as producers.
Nearly all such organisms originally draw their energy from the sun. Plants and other use solar energy via a process known as to convert raw materials into organic molecules, such as, whose bonds can be broken to release energy. A few, however, depend entirely on energy extracted by from, or other non- energy sources.
Some of the energy thus captured produces and energy that is available for growth and development of other forms. The majority of the rest of this biomass and energy are lost as waste molecules and heat. The most important processes for converting the energy trapped in chemical substances into energy useful to sustain life are and. Study and research Structural.
Schematic of typical animal depicting the various and structures. Is the study of biology at the molecular level.
This field overlaps with other areas of biology, particularly those of and. Molecular biology is a study of the interactions of the various systems within a cell, including the interrelationships of DNA, RNA, and protein synthesis and how those interactions are regulated. The next larger scale, studies the structural and properties of, including their internal, interactions with other cells, and with their. This is done on both the and levels, for unicellular organisms such as, as well as the specialized cells of multicellular organisms such as. Understanding the structure and function of cells is fundamental to all of the biological sciences.
The similarities and differences between cell types are particularly relevant to molecular biology. Is a treatment of the macroscopic forms of such structures and organ systems. Is the science of, and the variation of. Genes encode the information needed by cells for the synthesis of proteins, which in turn play a central role in influencing the final of the organism.
Genetics provides research tools used in the investigation of the function of a particular gene, or the analysis of. Within organisms, genetic information is physically represented as, within which it is represented by a particular of amino acids in particular. Studies the process by which organisms grow and develop. Developmental biology, originated from, studies the genetic control of, and 'cellular,' which is the process that progressively gives rise to, and. For developmental biology include the round worm, the fruit fly, the zebrafish, the mouse, and the weed. (A model organism is a that is extensively studied to understand particular biological, with the expectation that discoveries made in that organism provide insight into the workings of other organisms.) Physiological. Main article: Physiology is the study of the mechanical, physical, and biochemical processes of living organisms function as a whole.
The theme of 'structure to function' is central to biology. Physiological studies have traditionally been divided into and, but some principles of physiology are universal, no matter what particular is being studied.
For example, what is learned about the physiology of cells can also apply to human cells. The field of animal physiology extends the tools and methods of to non-human species. Plant physiology borrows techniques from both research fields. Physiology is the study the interaction of how, for example, the, and systems, function and interact. The study of these systems is shared with such oriented disciplines as and.
Evolutionary is concerned with the origin and descent of, and their change over time. It employs scientists from many taxonomically oriented disciplines, for example, those with special training in particular such as, or, but are of use in answering more general questions about evolution. Evolutionary biology is partly based on, which uses the record to answer questions about the mode and tempo of evolution, and partly on the developments in areas such as. In the 1980s, re-entered evolutionary biology after its initial exclusion from the through the study of., and are related fields often considered part of evolutionary biology.
Main article: Multiple events create a tree structured system of relationships between species. The role of is to study these relationships and thus the differences and similarities between species and groups of species.
However, systematics was an active field of research long before evolutionary thinking was common. 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: (originally Archaebacteria); (originally Eubacteria) and (including, and ) These domains reflect whether the cells have nuclei or not, as well as differences in the chemical composition of key biomolecules such as. Further, each kingdom is broken down recursively until each species is separately classified.
The order is:;;;;;;;. Outside of these categories, there are obligate intracellular that are 'on the edge of life' in terms of activity, meaning that many scientists do not actually classify such structures as alive, due to their lack of at least one or more of the fundamental functions or characteristics that define life. They are classified as,. The scientific name of an organism is generated from its genus and species. For example, humans are listed as. Homo is the genus, and sapiens the species. When 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 may be italicized or underlined. The dominant classification system is called the. It includes ranks and. How organisms are named is governed by international agreements such as the (ICN), the (ICZN), and the (ICNB). The classification of, and all other sub-viral agents that demonstrate biological characteristics is conducted by the (ICTV) and is known as the International Code of Viral Classification and Nomenclature (ICVCN). However, several other viral classification systems do exist.
A merging draft, BioCode, was published in 1997 in an attempt to standardize nomenclature in these three areas, but has yet to be formally adopted. The BioCode draft has received little attention since 1997; its originally planned implementation date of January 1, 2000, has passed unnoticed. A revised BioCode that, instead of replacing the existing codes, would provide a unified context for them, was proposed in 2011. However, the of 2011 declined to consider the BioCode proposal. The remains outside the BioCode, which does not include viral classification.
Main articles:, and is the study of the distribution and abundance of, the interaction between them and their. An organism shares an environment that includes other organisms and as well as local (non-living) such as and. 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 small scales. A microscopic responding to a local sugar gradient is responding to its environment as much as a lion searching for food in the African. For any species, can be,. Matters become more complex when two or more species interact in an.
Ecological systems are studied at several different levels, from the scale of the ecology of individual organisms, to those of, to the and finally the. The term is often used interchangeably with, although population biology is more frequently used in the case of, and, while the term population ecology is more commonly applied to the study of plants and animals. Ecology draws on many subdisciplines. Is the study of animal (particularly that of social animals such as and ), and is sometimes considered a branch of zoology. Ethologists have been particularly concerned with the of behavior and the understanding of behavior in terms of the theory of.
In one sense, the first modern ethologist was, whose book, influenced many ethologists to come. Studies the spatial distribution of organisms on the, focusing on such topics as, and, and. Basic unresolved problems in biology. Main article: Despite the profound advances made over recent decades in our understanding of life's fundamental processes, some basic problems have remained unresolved. One of the major unresolved problems in biology is the primary adaptive function of sex, and particularly its key processes in eukaryotes of meiosis and homologous recombination.
One view is that sex evolved primarily as an adaptation that promoted increased genetic diversity (see references e.g. An alternative view is that sex is an adaptation for promoting accurate DNA repair in germ-line DNA, and that increased genetic diversity is primarily a byproduct that may be useful in the long run. Another basic unresolved problem in biology is the biologic basis of aging. At present, there is no consensus view on the underlying cause of aging.
Various competing theories are outlined in. Branches These are the main branches of biology: For a more detailed list, see.
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Belmont, CA: Wadsworth. External links Wikibooks has more on the topic of: Wikisource has original works on the topic: Look up in Wiktionary, the free dictionary. Wikiversity has learning resources about. at Curlie (based on ).
Campbell Biology 9th Edition Chapter 7 Summary Great Gatsby
– Idaho National Laboratory.: A multi-authored, distributed Internet project containing information about phylogeny and biodiversity. Journal links.
A peer-reviewed, open-access journal published by the.: General journal publishing from all areas of biology.: A journal publishing Biology papers of general interest.: Internationally renowned science journal – see sections of the life sciences.: A biological journal publishing significant peer-reviewed scientific papers.: An journal publishing of broad relevance.