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from article Piciformes
Red-headed woodpecker (Melanerpes erythrocephalus) in Desoto National Wildlife Refuge, Iowa. (Photo by Dave Menke/U.S. Fish and Wildlife Service)
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from article Otter
North American river otter (Lontra canadensis). (Credit: Alan and Sandy Carey/Getty Images)
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from article Otter
Sea otter (Enhydra lutris) in the water off the coast of Moss Landing, California. (Credit: Lilian Carswell/U.S. Fish and Wildlife Service)
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from article Forensic botany
Surface of a green bean pod, showing its spines using (a) light microscope (courtesy of David O. Norris) and (b) scanning electron microscope (courtesy of Meredith Lane).
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from article Anthropology
Fossil skulls of four different species of Homo (clockwise from upper left): Homo neanderthalensis, Homo antecessor, Homo erectus, and Homo sapiens. Each skull shows different anatomical variations. (Credit: creativemarc/Shutterstock)
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from article Anthropology
The indigenous inhabitants of Siberut Island (West Sumatra, Indonesia) are known as the Mentawai people. They live a seminomadic hunter-gatherer life in the coastal and rainforest environments of the island. (Credit: Chanwit Whanset/Shutterstock)
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from article Dentition
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from article Pain
Neurophysiology of incoming pain. Sensation from peripheral receptors travels along specific pain nerves, and is modulated throughout the spinal cord and brain. (Copyright © McGraw-Hill Education)
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from article Echiura
Echiuran anatomy. (a) External anatomy, ventral view. (b) Internal anatomy, dorsal view. A, anus; AV, anal vesicles; G, gut (middle section removed for clarity); M, mouth; N, nephridia (egg and sperm storage organs); S, setae; VNC, ventral nerve…
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from article Atomic force microscopy
Principle of AFM.
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from article Atomic force microscopy
Application of AFM imaging to lipid membranes. (a) Nanostructures with well-defined bendings and a ∼30 nm periodicity, formed at the surface of a mixed dipalmitoylphosphatidylcholine/surfactin bilayer supported on mica. (b) Another type of…
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from article Atomic force microscopy
Application of AFM force spectroscopy to the detection of single molecular recognition events. Force–distance curves were recorded between an AFM tip and a substrate functionalized with oligoglucose and concanavalin A, respectively. The ∼100 pN…
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from article Schizomida
Schizomus sawadai. (After K. Sekiguchi and T. Yamasaki, A redescription of “Trithyreus sawadi” (Uropygi: Schizomidae) from the Bonin Islands, Acta Arachnol., 24(2):73–81, 1972)
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from article Data structure
Linear array of integers.
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from article Data structure
A stack, a linear list in which elements are inserted or deleted only at one end.
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from article Data structure
A queue, a linear list that permits insertion at one end and deletion at the other.
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from article Data structure
Singly linked list or one-way chain.
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from article Data structure
Diagram representing a directed graph.
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from article Data structure
Example of a tree.
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from article Data structure
Linked storage representation for a binary tree.
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from article Signal transduction
Different receptors and their mechanism of action: G-protein–coupled receptor (GPCR), receptor tyrosine kinase (RTK), adenylyl cyclase (AC).
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from article Signal transduction
Steps in the activation of the MAPK pathway leading to cell proliferation.
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from article Signal transduction
Steps in the glucagon-stimulated release of glucose stores from cells.
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from article Notomyotida
Some diagnostic features of representative Notomyotida. (a) Paxillae and one pectinate pedicellariae of Cheiraster richardsoni. (b) Benthopecten pentacanthus.
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from article Jerboa
Jerboa. (Credit: Pekka Fågel)
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from article Ratites
Ostrich (Struthio camelus massaicus). (Photo courtesy of Gerald and Buff Corsi, copyright © California Academy of Sciences)
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from article Ratites
Greater rhea (Rhea americana). (Photo courtesy of Dr. Lloyd Glenn Ingles, copyright © California Academy of Sciences)
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from article Choanoflagellida
A linear colony of the choanoflagellate, Desmarella moniliformis.
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from article Nitrogen-fixing trees
Nitrogen-fixing Rhizobium bacteria form nodules on the roots of various legume trees. (Copyright © McGraw Hill)
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from article Nitrogen-fixing trees
A perennial nodule, several years old, formed on the roots of common or black alder (Alnus glutinosa) by symbiosis with Frankia (a nitrogen-fixing bacterium). (Copyright © McGraw Hill)
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from article Lipoprotein
Structural model of a lipoprotein.
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from article Machine learning
Machine-learning algorithms will help self-driving cars reliably handle unexpected situations they encounter on the road. (Credit: Karsten Neglia/Shutterstock)
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from article Trematoda
Phylogeny of the Neodermata. Note that the monophyly of the Neodermata has been confirmed by many morphological and DNA studies. The phylogeny of the various neodermatan subgroups may have to be revised on the basis of studies using mitochondrial…
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from article Trematoda
Furcocercaria of Schistosoma. Note the forked tail.
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from article Trematoda
Eggs of Schistosoma species. Note the differently developed spine and egg shape in the various species shown.
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from article Trematoda
Paragonimus species. Note the spinose tegument. Worms are about 1.5 cm (0.6 in.) in length.
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from article Anthropocene extinction
The relationship between species extinctions and the human population on Earth since the year 1800. As the human population has increased, so too have the numbers of species extinctions. The numbers have been so great that the current Anthropocene…
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from article Acantharea
Representatives of the Acantharea; Acanthometra pellucida, (a) showing axial rods extending through the central capsule, and myonemes (myophrisks) extending from the rods to the sheath; (b) contracted myophrisks with expanded sheath; and (c) relaxed…
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from article Vitamin K
Vitamin K. (a) Natural forms. (b) Regeneration of the hydroquinone for γ-carboxyglutamate (Gla) synthesis; Glu = glutamic acid. Vitamin K functions by carboxylating certain glutamate residues in a few proteins. With each carboxylation reaction, a…
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from article Vertebrata
The subphylum Vertebrata constitutes the largest natural group (clade or monophyletic group) of chordate animals (members of the phylum Chordata). The asterisk indicates that birds are included in the reptile group. (Copyright © McGraw Hill)
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from article Ophiurida
Brittle star, Ophiolepis impressa (order Ophiurida, family Ophiolepididae), found on coral reefs in the tropical western Atlantic. (After G. Hendler et al., Sea Stars, Sea Urchins and Allies: Echinoderms of Florida and the Caribbean, Smithsonian…
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from article Proteasome
Most intracellular proteins destined for degradation by the 26S proteasome are bound to multiple ubiquitin molecules through the action of three enzymes: a ubiquitin-activating enzyme (E1), a ubiquitin-conjugating enzyme (E2), and a…
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from article Proteasome
Three-dimensional computerized reconstruction from electron microscopic images of the 26S proteasome. This large proteolytic complex is composed of about 50 different subunits that form subparticles, the 20S proteasome and the 19S regulatory…
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from article Neritimorpha
Female Nerita laying egg capsules.
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from article Neritimorpha
Sea grass snail Smaragdia with cryptic green coloration.
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from article Neritimorpha
Red-blooded Phenacolepas limpets.
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from article Glutathione
Reduced and oxidized forms of glutathione.
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from article Glutathione
γ-Glutamyl cycle. See text for description of steps.
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from article Hedgehog
European hedgehog (Erinaceus europaeus). (Photo by James Brian Bottomley and Sheila Bottomley)
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from article Gastornithiformes
Gastornis giganteus (reconstruction), an extinct flightless bird belonging to the order Gastornithiformes. (Photo courtesy of the American Museum of Natural History, New York)
