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from article Information processing (psychology)

Vertical associative memory where concepts are grouped into phrases and propositions by associating each concept to a higher-order node that represents the entire group. (Copyright © McGraw-Hill Education)

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from article Octopoda

An octopod swimming in the ocean. (Credit: Getty Images/iStockphoto)

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from article Octopoda

Hapalochlaena maculosa, the Southern or lesser blue-ringed octopus, has vivid, small blue rings on its body and arms, highlighted with black outlines. Location: Mrs. Watson's Bay, Lizard Island, Great Barrier Reef, Australia. (Credit: Clyde F. E.…

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from article Octopoda

Hapalochlaena fasciata, the blue-lined octopus, has vivid blue lines on its body and rings on its arms, highlighted with black outlines. Location: Long Reef, New South Wales, Australia. (Credit: Clyde F. E. Roper)

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from article Octopoda

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from article Polyplacophora

Chiton on a rock surface. (Photo courtesy of the NOAA Okeanos Explorer Program, National Oceanic and Atmospheric Administration)

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from article Polyplacophora

Polyplacophoran mollusk (chiton): (a) dorsal view; (b) ventral view.

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from article Pituitary gland disorders

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from article Pituitary gland disorders

Infarction (obstruction of the blood supply) of the pituitary gland. This pituitary gland is almost entirely infarcted. Only a thin rim of viable cells remains (arrow). Pituitary infarcts can occur during pregnancy (Sheehan's disease) or as a result…

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from article Strychnos

Strychnos nux-vomica: close-up view of leaves and flowering branch. (Photo courtesy of Dinesh Valke)

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from article Aconchulinida

Aconchulinida. (a) Penardia cometa. (b) Penardia mutabilis.

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from article Phonoreception

Generalized sketch of the vertebrate labyrinth. The three cristae, macula ultriculi, and macula sacculi are always present in vertebrates, and the other endings appear as indicated, with a few exceptions.

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from article Phonoreception

Diagram (from above) of the two labyrinths of an ostariophysan fish and their connections with the swim bladder through the Weberian ossicles.

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from article Phonoreception

Simplified diagram of the frog ear.

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from article Phonoreception

Diagram of the ear of a snake. The nonauditory parts and endings are not shown.

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from article Phonoreception

Auditory sensitivity of a wood turtle (Clemmys insculpta), as shown by the potentials produced in its ear by sounds. The curve shows the sound pressure necessary to produce a potential of 0.3 microvolt.

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from article Phonoreception

Graph showing threshold sensitivity in the bullfinch (mean of four birds). (Credit: J. Schwartzkopff)

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from article Phonoreception

Auditory thresholds in primates. The curves show the sound pressures that are barely audible for humans, chimpanzees, rhesus monkeys, and marmosets.

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from article Phonoreception

Diagram of the ear of a grasshopper.

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from article Phonoreception

Auditory thresholds of the katydid (Conocephalus strictus). Sensitivity is greatest in the 7000–60,000-Hz region. (Credit: E. G. Wever and J. A. Vernon)

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from article Siphonaptera

Head of Spilopsyllus cuniculi (rabbit flea), with extended mouthparts.

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from article Guided missile

A U.S. Navy ship fires a Tomahawk cruise missile at a target in Libya as part of Operation Odyssey Dawn in 2011. (Credit: MC3 Jonathan Sunderman/US Navy/DoD)

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from article Guided missile

A V-2 rocket constructed by the U.S. military lifts off in this historical photo. Production and development of V-2 rockets continued in the United States after the defection of German aerospace engineers during World War II. (Credit: U.S. Army)

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from article Colemanite

Fundamental building block in the crystal structure of colemanite.

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from article Colemanite

Crystal structure of colemanite viewed down the a axis. The 〈Δ2□&x3009 x232A; rings link to form chains of borate polyhedra parallel to the c axis.

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from article Atomic bomb

The mushroom cloud over Nagasaki, Japan, after an atomic bomb was dropped by U.S. aircraft on August 9, 1945. (Credit: Everett Historical/Shutterstock)

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from article Atomic bomb

Conceptual diagrams illustrating the main features of (a) implosion type and (b) gun-barrel type of fission weapons. (Credit: A. DeVolpi)

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from article Breadfruit

Breadfruit (Artocarpus altilis), showing the rounded (or elliptic) fruit and the cylindrical staminate flower cluster. (Photo courtesy of Forest and Kim Starr)

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from article Island biogeography

Equilibrium number of species (Sequilibrium) is determined by the intersection of the immigration ( I ) and extinction ( E ) rate curves. P is the maximum number of species in the source pool.

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from article Notch signaling

Notch-ligand interactions. Two Notch ligands, Delta and Serrate, are shown on the signal-sending cell (left). These ligands are distinguished by differing numbers of EGF-like repeats (indicated by the light boxes) and an extracellular cysteine-rich…

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from article Folic acid

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from article Digenea

Diagrams of various adult types of digenean trematodes. (After R. M. Cable, An Illustrated Laboratory Manual of Parasitology, Burgess, Minneapolis, 1940)

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from article Digenea

Digenean trematode life cycle. (After R. M. Cable, An Illustrated Laboratory Manual of Parasitology, Burgess, Minneapolis, 1940)

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from article Hydroponics

Green- and red-leaf lettuce growing in a hydroponic vegetable garden on a bamboo fence. The pipes, which supply nutrients and water, are part of the hydroponic system. (Credit: Piyachok Thawornmat, Shutterstock)

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from article Hydroponics

Hydroponic techniques: (a) aerated standing culture; (b) flowing-solution culture with standing solution; (c) nutrient film technique; (d) aeroponics.

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from article Emerald

Emerald crystals. (Credit: Reimphoto/Getty Images)

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from article Mango

Tommy Atkins cultivar of mango (Mangifera indica) growing in Florida. (Credit: Wilhelmina Wasik/Agricultural Research Service, U.S. Department of Agriculture)

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from article Urinary bladder

Light micrograph of the healthy transitional epithelium tissue (stained by hematoxylin and eosin) of a urinary bladder. The transitional epithelium is a type of tissue consisting of multiple layers of epithelial cells, which can contract and expand.…

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from article Urinary bladder

Types of tubal bladders: (a) duplex; (b) bilobed; (c) simplex, with ureters united; (d) simplex, with separate ureters. (Credit: H. E. Walter and L. P. Sayles)

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from article Tomato

Tomatoes (Solanum lycopersicum). (Credit: Peggy Greb, Agricultural Research Service, U.S. Department of Agriculture)

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from article Tomato

Tomato affected by anthracnose (caused by the fungus Colletotrichum phomoides). (Credit: U.S. Department of Agriculture Cooperative Extension Slide Series, Clemson University)

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from article Tomato

Tomatoes showing blossom-end rot. (Credit: Mary Ann Hansen, Virginia Polytechnic Institute and State University)

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from article Learning

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from article Learning

Brain activity can be recorded in various ways, from single-cell activity (top tracing) to the familiar electrical patterns ("brain waves") of an electroencephalogram (bottom tracing). (Credit: Based on an original drawing by C. Cotman and J.…

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from article Pine nut

Pine nuts in their hard shell (Mexican piñon pine, Pinus cembroides). (Photo by Steve Hurst, U.S. Department of Agriculture–Natural Resources Conservation Service PLANTS Database)

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from article Pine nut

Cone containing pine nuts (stone pine, Pinus pinea). (Photo by Vito Buono, Bari, Italy)

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from article Biofilm

Biofilms are highly structured communities of microorganisms that are surface-associated or attached to one another, and are enclosed within a self-produced protective extracellular matrix. Biofilm formation and actions involve a number of stages:…

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from article Ctenothrissiformes

A Cretaceous ctenothrissiform fossil, Ctenothrissa sp. (order Ctenothrissiformes), on a limestone matrix found in Lebanon. Size: 90 mm (3.5 in.). (Photo courtesy of The Virtual Fossil Museum)

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from article Pyroclastic rock

Pyroclastic rock. Bombs from Mauna Kea, Hawai'i, USA. (Credit: J. P. Lockwood/USGS Photo Library, Denver, CO)

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from article Pyroclastic rock

Distribution downwind of the pyroclastic fall deposit from the climactic eruption of Mount St. Helens, Washington, on May 18, 1980. The contours (isopachs) are drawn through points of measured equal thickness (in centimeters) of this ash layer.…

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from article Pyroclastic rock

Aerial view in March 1998 of the fan-shaped pyroclastic delta formed by repeated entries of pyroclastic flows and surges into the Caribbean Sea during the Soufrière Hills Volcano eruption in 1996–1997. (Credit: R.P. Hoblitt, USGS)

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from article Pyroclastic rock

Observed or postulated mechanisms for the generation of pyroclastic flow and surge deposits. (a, b) Mechanisms that commonly produce block-and-ash flow deposits. (b, c) Mechanisms that trigger laterally directed blasts. (d–f) Mechanisms that…

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from article Pyroclastic rock

Some variations in pyroclastic rock formations. (a) Layers of pyroclastic fall deposits from the eruption plume of the June 15, 1991, explosive eruption of Mount Pinatubo (Luzon, Philippines). This exposure, located about 9 km (5.5 mi) southeast of…

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from article Lung

Human lungs. (a) The trachea bifurcates as the right and left primary bronchi that enter each lung. The bronchi subdivide further to form the bronchial tree. (b) Color-coded view of the major branches of the bronchial tree. (Copyright © McGraw Hill)

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from article Animal testing

Mice are the most commonly used vertebrate species in animal testing and research. (Credit: Dolores Bonaparte)

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from article Animal testing

The use of animals in biomedical research remains essential, but the handling of these sentient beings must be done humanely to minimize and prevent animal harm. (Credit: U.S. Department of Agriculture)

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from article Common cold

Adenovirus structure. An adenovirus binds to the host cell via its fiber through the knob at the end of the fiber "spikes" on the capsid (protein coat) surface. (Credit: M. K. Cowan and H. Smith; copyright © McGraw Hill)

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from article Common cold

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from article Common cold

Life cycle of a double-stranded DNA virus, such as an adenovirus. The virus attaches to specific receptors, after which it is taken up by the cell. Following entry into the cell, the viral capsid (protein coat) is digested, releasing DNA, which…

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from article Common cold

Electron micrograph (tinted green) of human coronavirus 229E particles. Coronaviruses are named for the corona, or halo, surrounding the capsid (protein coat). The crown-like corona results from the presence of viral spikes protruding from the viral…

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from article Earth's interior

Speculative models of the interiors of the terrestrial planets. All are rocky, divided into a crust (not shown here), mantle, and metallic core. (After R. T. Merrill and M. W. McElhinny, The Earth's Magnetic Field, Academic Press, 1983)

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from article Earth's interior

Preliminary Reference Earth Model (PREM) for P- and S-wave velocities, vp and vs, and density ρ. In the part of the upper mantle where the model is anisotropic, velocities are given in both the vertical and horizontal direction. The broken lines…

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from article Earth's interior

Variations of gravity and pressure inside the Earth. 1 m = 3.3 ft. 1 megabar = 100 GPa. (After P. Melchior, The Physics of the Earth's Core, Pergamon Press, 1986)

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from article Earth's interior

Density versus depth for several mantle constituents along the 1400°C (2552°F) adiabat. Data points show the density variation of PREM. All three constituents shown here contain magnesium-rich silicates. (After D. L. Anderson, Where on Earth is the…

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from article Earth's interior

P-wave velocity anomalies above the core–mantle boundary in terms of spherical harmonics up to degree and order 6, obtained by inverting P-wave travel time data. Positive perturbations indicate faster-than-average material. Contour interval = 25…

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from article Earth's interior

Speculative, schematic model of the core–mantle boundary layer. A heterogeneous chemical boundary layer is embedded in a thermal boundary layer. Large-scale mantle circulation transports chemical heterogeneity to the base of the mantle as well as…

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from article Earth's interior

Schematic temperature profile of the mantle. Subsequent estimates of core temperature are higher than suggested in the figure; the temperature jump across the thermal boundary layer at the base of the mantle will then be correspondingly higher. °F =…

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from article Earth's interior

Schematic temperature profile of the core. The melting-point curve for the core is substantially below the melting point of pure iron. All temperatures may have to be raised to correspond with further estimates of the melting point of iron. °F = (K…

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from article Earth's interior

Contour plots of the radial component of the magnetic field at the core–mantle boundary (a) for the year 1715 and (b) for 1980. The contour interval is 100 microteslas; solid-line contours represent flux into the core, and broken-line contours…

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from article Circadian clock (plants)

Three-module circadian clock system.

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from article Circadian clock (plants)

Model of the Arabidopsis circadian clock, showing light input (bold arrow), the central oscillator (large box) and output/response (tinted arrows). Light signals synchronize the clock via the cryptochromes (cry) and phytochromes (phy). These are…

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from article Acari

Parasitiformes body plan. Lateral view of a predatory adult female Mesostigmata showing major body regions and important structures. Scale bar = 0.1 mm (0.004 in.). (Scanning electron micrograph by D. E. Walter)

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from article Acari

Acariformes body plan. (a) Adult female Oribatida (Sarcoptiformes) in lateral view showing major body regions and important structures. (b) Hexapod larva (Trombidiformes): dorsal view of a chigger, a parasite of vertebrates. (c) Octopod deutonymph…

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from article Anthrax

A color-enhanced scanning electron micrograph showing splenic tissue from a monkey with inhalation anthrax. Rod-shaped bacilli of Bacillus anthracis (yellow) and an erythrocyte (red) are shown. (Credit: Arthur Friedlander/National Institute of…

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from article Anthrax

Micrograph (stained with hematoxylin and eosin) showing submucosal hemorrhage in the small intestine of a person fatally affected by gastrointestinal anthrax. (Credit: Marshal Fox/Centers for Disease Control and Prevention)

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from article Neuron

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from article Tumor virus

Under certain conditions, human papillomaviruses are capable of causing cancer in humans. (Credit: Laboratory of Tumor Virus Biology, National Cancer Institute)

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from article Mutagens and carcinogens

Arsenic is a known carcinogen. In this graphical example, more than half of the mice exposed to arsenic in their drinking water [at concentration levels of 50 and 500 parts per billion (ppb)] showed increased incidences of lung tumors (compared to a…

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from article Mutagens and carcinogens

Proflavin is a chemical disinfectant agent against bacteria, causing mutagenic DNA changes (such as the insertion or deletion of a DNA base pair). However, it is carcinogenic in mammals. Thus, it is used only for the disinfecting of surfaces or for…

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from article Mutagens and carcinogens

Model of carcinogenesis. Changes often occur in the growth properties of normal cells, leading to cancer cells that are not responsive to normal regulatory controls and can eventually give rise to a visible neoplasm or tumor. The main stages of the…

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from article Ecosystem

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from article Ecosystem

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from article Ecosystem

Food chains are limited by energy transfer. In this illustration, energy is transferred from the Sun to a plant (producer) to a primary consumer and to a secondary consumer. Energy is used by the producer and consumer organisms and is lost to the…

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from article Ecosystem

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from article Ecosystem

General model of the carbon cycle in ecosystems: (A) carbon dioxide (CO2) from the air; (B) carbon from decomposition; (C) carbon from fossil fuels; (D) natural events (for example, forest fires and volcanoes) release CO2 into the air. (Copyright ©…

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from article Autophagy

Modes of autophagy in yeast and mammalian cells. Macroautophagy involves the uptake of cytoplasm at a site away from the lysosome or vacuole. The origin of the sequestering membrane is not known, but it likely includes multiple sources such as the…

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from article Autophagy

Basic steps involved in macroautophagy, shown with the structural intermediates. See the text for full details.

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from article Autophagy

The cytoplasm-to-vacuole targeting (Cvt) pathway is an example of selective autophagy. The schematic illustrates the steps of the Cvt pathway and also shows electron micrographs of the sequestration event. Precursor aminopeptidase I (prApe1) forms a…

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from article Autophagy

Atg8 tagged with white fluorescent protein (GFP-Atg8) can be used to monitor autophagosome formation. Cells in growing conditions (for example, in the presence of nitrogen; +N) carry out a basal level of macroautophagy and typically display a single…

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from article Cell cycle

Phases of the eukaryotic cell cycle. Interphase is subdivided into three phases: gap phase 1 (G1), synthesis (S), and gap phase 2 (G2). M phase, which follows interphase, consists of mitosis (nuclear division) and cytokinesis (cell division). G0…

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from article Cell cycle

During cytokinesis (cell division), the cell pinches into two parts between the separated daughter nuclei. At the end of this process, the two daughter cells often remain tethered by a thin "midbody" of microtubules. Once this midbody breaks, the…

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from article Cell cycle

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from article Pituitary gland

The pituitary, also known as the hypophysis, is a pea-sized gland situated at the base of the brain. The hypothalamus is designed and anatomically positioned to receive a diversity of messages from external and internal sources that can be…

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from article Pituitary gland

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from article Salicylate

Chemical structures of (a) salicylate, the conjugate base of (b) salicylic acid, and the nonsteroidal anti-inflammatory drug (NSAID) (c) acetylsalicylic acid (aspirin).

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from article Meningococcus

A photomicrograph reveals the presence of the bacterium Neisseria meningitidis, which can be pathogenic, leading to meningococcal meningitis. (Credit: James Volk/Centers for Disease Control and Prevention)

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from article Poplar

Quaking aspen (Populus tremuloides). (Photo courtesy of North Dakota State Soil Conservation Committee, USDA–NRCS PLANTS Database)

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from article Poplar

Common poplar species. (a) Quaking aspen (P. tremuloides); leaf scar with an axial bud, leaf, and twig. (b) Bigtooth aspen (P. grandidentata); leaf, terminal bud, and twig. (c) Cottonwood poplar (P. deltoides); leaf, leaf scar, terminal bud, and…

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from article Hydrological consequences of global warming

The hydrologic cycle is characterized by evaporation and transpiration from the surfaces; transport of water vapor in the atmosphere by the wind, clouds, and precipitation; and water storage in snow, glaciers, groundwater, and oceans. Units: 1000…

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from article Hydrological consequences of global warming

Spatial patterns of climate model projections of (a) precipitation, (b) soil moisture, (c) runoff, and (d) evaporation for 2090–2099 under the mid-range A1B emission scenario from the Intergovernmental Panel for Climate Change 2007. (Climate Change…

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