Phylum Chordata classification - Unacademy Sexes are separate and gametes are released into the water through the atriopore for external fertilization. The name "chordate" comes from the first of these synapomorphies, the notochord, which plays a significant role in chordate structure and movement. A coelom also is present in some more distantly related phyla, including Annelida, Arthropoda, and Mollusca, but the main organs of the body are arranged differently in these phyla. Some chordate lineages may only be found by DNA analysis, when there is no physical trace of any chordate-like structures. (turtles and their extinct relatives). Jan 9, 2023 OpenStax. The four defining characteristics of chordates are: Dorsal, hollow nerve tube: Contains nervous tissue and forms during embryonic development. In vertebrate fishes, the pharyngeal slits are modified into gill supports, and in jawed fishes, into jaw supports. Animals in the phylum Chordata share four key features that appear at some stage during their development (often, only during embryogenesis) (: The chordates are named for the notochord: a flexible, rod-shaped structure that is found in the embryonic stage of all chordates and also in the adult stage of some chordate species. Animals in the phylum Chordata share four key features that appear at some stage during their development: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail (Figure 2). A second step was the evolution of the amniotic egg, which, similar to the evolution of pollen and seeds in plants, freed terrestrial animals from their dependence on water for fertilization and embryonic development. Cephalochordates usually live partially buried in marine sand and gravel. In some groups, some of these are present only during embryonic development. 29.1: Chordates - Biology LibreTexts Traditionally, Cephalochordata and Craniata were grouped into the proposed clade "Euchordata", which would have been the sister group to Tunicata/Urochordata. { "29.1A:_Characteristics_of_Chordata" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "29.1B:_Chordates_and_the_Evolution_of_Vertebrates" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "29.1C:_The_Evolution_of_Craniata_and_Vertebrata" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "29.1D:_Characteristics_of_Vertebrates" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()" }, { "29.01:_Chordates" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "29.02:_Fishes" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "29.03:_Amphibians" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "29.04:_Reptiles" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "29.05:_Birds" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "29.06:_Mammals" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "29.07:_The_Evolution_of_Primates" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()" }, [ "article:topic", "authorname:boundless", "showtoc:no", "license:ccbysa", "columns:two", "cssprint:dense", "licenseversion:40" ], https://bio.libretexts.org/@app/auth/3/login?returnto=https%3A%2F%2Fbio.libretexts.org%2FBookshelves%2FIntroductory_and_General_Biology%2FBook%253A_General_Biology_(Boundless)%2F29%253A_Vertebrates%2F29.01%253A_Chordates%2F29.1A%253A_Characteristics_of_Chordata, \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}}}\) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\), 29.1B: Chordates and the Evolution of Vertebrates, Identify the key features of the chordates. [15] While it is structured so as to reflect evolutionary relationships (similar to a cladogram), it also retains the traditional ranks used in Linnaean taxonomy. Chordates are common in all major habitats. Its anatomy of Pikaia closely resembles that of the extant lancelet in the genus Branchiostoma. Introduction. All chordates are deuterostomes possessing a notochord. Get a Britannica Premium subscription and gain access to exclusive content. Here we will consider the traditional groups Agnatha, Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves, and Mammalia, which constitute classes in the subphylum Vertebrata/Craniata. Learning Objectives Identify the key features of the chordates Key Takeaways Key Points These characteristics are only present during embryonic development in some chordates. Some invertebrate chordates use the pharyngeal slits to filter food out of the water that enters the mouth. The 1,600 species of Urochordata are also known as tunicates (Figure 29.5). Invertebrate Chordates: Overview & Examples - Study.com They also have a segmented body with a coelom and bilateral symmetry. Animals in the phylum Chordata share five key characteristics that appear at some stage during their development: a notochord, a dorsal hollow (tubular) nerve cord, pharyngeal gill arches or slits, a post-anal tail, and an endostyle/thyroid gland ( Figure 29.3 ). We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. Legal. A cranium is a bony, cartilaginous, or fibrous structure surrounding the brain, jaw, and facial bones (Figure 29.7). Creative Commons Attribution License These four traits, shown in Figure below, define the chordate phylum. [49], The evolutionary relationships between the chordate groups and between chordates as a whole and their closest deuterostome relatives have been debated since 1890. The dorsal hollow nerve cord is part of the chordate central nervous system. These characteristics . Chordates enter into a wide variety of symbiotic relationships and are especially noteworthy as hosts for parasites. Wed love your input. The Craniata and Tunicata compose the clade Olfactores, which is sister to Cephalochordata. Updates? In contrast, the nervous system in protostome animal phyla is characterized by solid nerve cords that are located either ventrally and/or laterally to the gut. More than one classification and naming scheme is used for these animals. Chordates have a complete digestive system and a closed circulatory system. Pharyngeal slits are openings in the pharynx that develop into gill arches in bony fish and into the jaw and inner ear in terrestrial animals. A water current is created by cilia in the mouth, and is filtered through oral tentacles. 29.1D: Characteristics of Vertebrates - Biology LibreTexts Characteristics of Chordata. These innovations may be associated with the whole genome duplications that resulted in a quadruplication of the basic chordate genome, including the Hox gene loci that regulate the placement of structures along the three axes of the body. While every effort has been made to follow citation style rules, there may be some discrepancies. (credit: Ernest V. More; taken at Smithsonian Museum of Natural History, Washington, D.C.), Chen, J. Y., Huang, D. Y., and Li, C. W., An early Cambrian craniate-like chordate,, https://openstax.org/books/biology-2e/pages/1-introduction, https://openstax.org/books/biology-2e/pages/29-1-chordates, Creative Commons Attribution 4.0 International License, Describe the distinguishing characteristics of chordates, Identify the derived characters of craniates that sets them apart from other chordates, Describe the developmental fate of the notochord in vertebrates. http://cnx.org/contents/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8, Describe the distinguishing characteristics of chordates. Learning Objectives Identify the key features of the chordates Key Points Chordate evolution and the three-phylum system - Royal Society In some groups, some of these are present only during embryonic development. Which of the following statements about common features of chordates is true? We consider them separately only for convenience. Chordate - Definition, Characteristics and Examples - Biology Dictionary Chordata Characteristics & Groups | What are Chordate Features Phylum Chordata Body Symmetry & Characteristics - Study.com The post-anal tail is a posterior elongation of the body, extending beyond the anus. Within the amniotes, modifications of keratinous epidermal structures have given rise to scales, claws, hair, and feathers. chordate, any member of the phylum Chordata, which includes the vertebrates (subphylum Vertebrata), the most highly evolved animals, as well as two other subphylathe tunicates (subphylum Tunicata) and cephalochordates (subphylum Cephalochordata). In some terrestrial vertebrates, the tail also helps with balance, courting, and signaling when danger is near. One such study suggested that deuterostomes arose before 900million years ago and the earliest chordates around 896million years ago. It provides stiffness to . Deuterostome phylogeny. Figure 29.1 C. 1: Clade Craniata: Craniata, including this fish (Dunkleosteus), are characterized by the presence of a cranium, mandible, and other facial bones. In chordates, four common features appear at some point during development: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. Relatives of vertebrates are invertebrates. Chordate - Wikipedia It includes some 60,000 species. Amniotes are adapted for terrestrial living, and include mammals, reptiles, and birds. Asexual reproduction takes place in tunicates and in some vertebrates (females of some fish and lizards can reproduce without fertilization). The post-anal tail is a skeletal extension of the posterior end of the body, being absent in humans and apes, although present during embryonic development. Ah, I see that the lancelets are raising their mouthparts. Figure 1. Last Updated: April 7, 2019 Chordate Definition A chordate is an animal that belongs to the phylum Chordata, which is part of the Deuterostomes kingdom. The Chordata and Ambulacraria, together and possibly with the Xenacoelomorpha, are believed to form the superphylum Deuterostomia, although this has recently been called into doubt.[6]. Characteristics of Chordata. Tetrapod literally means four-footed, which refers to the phylogenetic history of various land vertebrates, even though in some of the tetrapods, the limbs may have been modified for purposes other than walking. The other two subphyla are invertebrate chordates that lack a backbone. The notocord is located between the digestive tube and the nerve cord, and provides rigid skeletal support as well as a flexible location for attachment of axial muscles. One of the first major steps was the emergence of the quadrupeds in the form of the amphibians. The three other defining characteristics (other characteristics that are not found in any . Animals in the phylumChordatashare five key chacteristics that appear at some stage during their development: a notochord, a dorsal hollow (tubular) nerve cord, pharyngeal gill arches or slits, a post-anal tail, and an endostyle/thyroid gland (Figure 2). Characteristics of Chordata. After that, some of the traits disappear or develop into other organs. Vertebrates are named for the vertebral column, composed of vertebraea series of separate, irregularly shaped bones joined together to form a backbone (Figure 29.8). [29] These consist of a series of bony or cartilaginous cylindrical vertebrae, generally with neural arches that protect the spinal cord, and with projections that link the vertebrae. The phylum Chordata consists of animals with a flexible rod supporting their dorsal or back sides. As an Amazon Associate we earn from qualifying purchases. Chordates | Boundless Biology | | Course Hero In vertebrates, the notochord is present during embryonic development, at which time it induces the development of the neural tube which serves as a support for the developing embryonic body. The notochord, however, is not found in the postembryonic stages of vertebrates; at this point, it has been replaced by the vertebral column (that is, the spine). Attempts to produce evolutionary "family trees" shows that many of the traditional classes are paraphyletic. In some chordates, the notochord acts as the primary axial support of the body throughout the animals lifetime. and you must attribute OpenStax. Animals in the phylum Chordata share four key features that appear at some stage during their development: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail ().In some groups, some of these are present only during embryonic development. The gill slits and some other features that are common among the hemichordates and the chordates originated before the chordates became a separate group. They have a well-developed musculature and can swim rapidly by undulating the body. In contrast, the nervous system in protostome animal phyla is characterized by solid nerve cords that are located either ventrally and/or laterally to the gut. Hermaphroditism (possessing both male and female reproductive organs) is found in tunicates and some fishes, but otherwise the sexes are separate. Tetrapods include amphibians, reptiles, birds, and mammals, and technically could also refer to the extinct fishlike groups that gave rise to the tetrapods. Chordates are capable of locomotion by means of muscular movements at some stage in life. A second step was the evolution of the amniotic egg, which, similar to the evolution of pollen and seeds in plants, freed terrestrial animals from their dependence on water for fertilization and embryonic development. The chordate life cycle begins with fertilization (the union of sperm and egg). [36][47] Pikaia, discovered much earlier (1911) but from the Mid Cambrian Burgess Shale (505 Ma), is also regarded as a primitive chordate. [27] The term Tunicata (Lamarck 1816) is recognised as having precedence and is now more commonly used. Characteristics of Chordata. Craniate. Chordates (video) | Crash Course: Biology | Khan Academy We recommend using a In some terrestrial vertebrates, the tail also helps with balance, courting, and signaling when danger is near. [39] It seems very likely the 555 million-year-old Kimberella was a member of the protostomes. Some of the most violent eruptions take place along convergent boundaries where one plate margin is forced beneath another. (In non chordate animals, the nerve cord is solid and runs along the bottom). Salps are sequential hermaphrodites, with younger female colonies fertilized by older male colonies. { "12.01:_Chordates" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.02:_Placental_Mammals" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.03:_Vertebrate_Characteristics" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.04:_Evolution_of_Modern_Mammals" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.05:_Vertebrate_Reproduction" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.06:_Vertebrate_Classification" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.07:_Vertebrate_Evolution" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.08:_Fish_Structure_and_Function" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.09:_Fish_Reproduction_and_Development" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.10:_Fish_Classification" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.11:_Fish_Evolution_and_Ecology" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.12:_Amphibian_Structure_and_Function" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.13:_Amphibian_Reproduction_and_Development" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.14:_Amphibian_Classification" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.15:_Amphibian_Evolution_and_Ecology" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.16:_Reptile_Structure_and_Function" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.17:_Reptile_Reproduction" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.18:_Reptile_Classification" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.19:_Reptile_Evolution" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.20:_Reptile_Ecology" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.21:_Bird_Structure_and_Function" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.22:_Bird_Reproduction" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.23:_Bird_Classification" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.24:_Bird_Evolution" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.25:_Bird_Ecology" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.26:_Mammal_Characteristics" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.27:_Mammal_Structure_and_Function" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.28:_Mammal_Endothermy" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.29:_Mammal_Living_and_Locomotion" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.30:_Marsupials" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.31:_Monotremes" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.32:_Mammal_Ancestors" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.33:_Evolution_of_Early_Mammals" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12.34:_Mammal_Classification" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()" }, { "00:_Front_Matter" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "01:_Introduction_to_Biology" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "02:_Cell_Biology" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "03:_Genetics" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "04:_Molecular_Biology" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "05:_Evolution" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "06:_Ecology" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "07:_Prokaryotes_and_Viruses" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "08:_Protists_and_Fungi" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "09:_Plants" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "10:_Animals" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "11:_Invertebrates" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "12:_Vertebrates" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "13:_Human_Biology" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "zz:_Back_Matter" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()" }, [ "article:topic", "showtoc:no", "authorname:ck12", "program:ck12", "license:ck12", "source@http://www.ck12.org/book/CK-12-Biology-Concepts" ], https://bio.libretexts.org/@app/auth/3/login?returnto=https%3A%2F%2Fbio.libretexts.org%2FBookshelves%2FIntroductory_and_General_Biology%2FBook%253A_Introductory_Biology_(CK-12)%2F12%253A_Vertebrates%2F12.01%253A_Chordates, \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}}}\) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\), source@http://www.ck12.org/book/CK-12-Biology-Concepts.