Biology
Biology studies the variety of life (clockwise from top-left) E. coli, tree fern, gazelle, Goliath beetle
Biology (from Greek βιολογία - βίος, bios, "life"; -λογία, -logia) is the study of life and a branch of the natural sciences which studies living organisms and how they interact with each other and their environment. It examines the structure, function, growth, origin, evolution, and distribution of living things. Also, it classifies and describes organisms, their functions, and how species come into existence. Five unifying principles form the foundation of modern biology: cell theory, evolution, gene theory, energy, and homeostasis.[1]
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.[2]
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; 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 and their environment interrelate.
Contents[hide]
1 Foundations of modern biology
1.1 Cell Theory
1.2 Evolution
1.3 Gene theory
1.4 Homeostasis
1.5 Energy
2 Research
2.1 Structural
2.2 Physiological
2.3 Evolution
2.4 Taxonomy
2.5 Ecology
3 See also
4 References
5 Further reading
6 External links
//
Foundations of modern biology
There are five unifying principles of biology [3]:
Cell theory. Cell Theory is the study of everything that involves cells and tissues. 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. Cell theory studies how cells are made, how they reproduce, how they interact with their environment, what they are composed of, and how the materials that make up a cell work and interact with other cell sections.
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 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 the genotype 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
Main article: Cell theory
Cell theory states that[4]:
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
Main article: 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 (see Common descent). This has led to the striking similarity of units and processes discussed in the previous section. 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 as well as by artificial selection or selective breeding.[5] 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 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.[6] 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.[7]
Gene theory
Schematic representation of DNA, the primary genetic material.
Main article: Gene
Biological form and function are passed on to the next generation by genes, which are the primary units of inheritance. Physiological adaptation 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
沒有留言:
張貼留言