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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 rocks

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from article Pyroclastic rocks

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 rocks

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. (Photograph by R.P. Hoblitt, USGS)

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from article Pyroclastic rocks

Observed or postulated mechanisms for the generation of pyroclastic flow and surge deposits (from W. E. Scott, 1989). (a, b) Mechanisms that commonly produce block-and-ash flow deposits. (b, c) Mechanisms that trigger laterally directed blasts.…

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from article Pyroclastic rocks

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 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 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 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 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 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 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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from article Biodiversity

Global biodiversity hotspots. There are more than 30 biodiversity hotspots located around the world. These areas have experienced severe habitat losses (at least 70%) as the result of human activities, hampering the work of conservationists in their…

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from article Biodiversity

A regional analysis of 25 oceanic regions shows that 92% of all known biodiversity falls into a dozen groups, of which crustaceans (for example, crabs, shrimps, and lobsters), mollusks (for example, snails, bivalves, squids, and octopus), and fish…

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from article Biodiversity

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from article Haplosporida

Spore of Urosporidium fuliginosum.

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from article Haplosporida

Stages in the development of Icthyosporidium giganteum.

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from article Micrometeorology

Soundings of temperature versus height for (a) day time and (b) nighttime obtained by radiosonde measurements during the Wangara experiment near Hay, New South Wales, Australia, in 1967. Soundings are shown for 9 A.M. through 9 P.M. on day 33 of the…

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from article Micrometeorology

The 3 P.M. sounding from Fig. 1a showing the layers of the daytime convective boundary layer.

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from article Urodela

A typical member of the order Urodela: the longtail salamander (Eurycea longicauda). (Credit: Ryan Hagerty/U.S. Fish and Wildlife Service)

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from article Urodela

Southern dwarf siren (Pseudobranchus axanthus), which has undergone limb degeneration and retains only tiny forelimbs. (Credit: U.S. Geological Survey)

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from article Urodela

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from article Urodela

California tiger salamander (Ambystoma californiense). (Credit: John Cleckler/U.S. Fish and Wildlife Service)

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from article Urodela

The two-toed amphiuma salamander (Amphiuma means). (Credit: Southeast Ecological Center, U.S. Geological Survey)

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from article Urodela

The northern red salamander (Pseudotriton ruber ruber) is a member of the family Plethodontidae. (Credit: Alicia Lafever/U.S. National Park Service)

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from article Spinal cord disorders

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from article Earth's heat flow

Geographic distribution of heat flow measurement sites. (After H. N. Pollack, S. J. Hurter, and J. R. Johnson, Heat flow from the Earth's interior: Analysis of the global data set, Rev. Geophys., 31(3):267–280, 1993)

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from article Earth's heat flow

Heat flow–versus–age relationships for continents and oceans. (After D. Sprague and H. N. Pollack, Heat flow in the Mesozoic and Cenozoic, Nature, 285:393–395, 1980)

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from article Earth's heat flow

Geographic distribution of 17 heat flow provinces where the linear relationship between measured heat flow and radiogenic heat production from near-surface rocks has been empirically determined. (After I. Vitorello and H. N. Pollack, On the…

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from article Earth's heat flow

Present-day global heat flow (degree 12 spherical harmonic representation). Contours are in milliwatts per square meter. (After H. N. Pollack, S. J. Hurter, and J. R. Johnson, Heat flow from the Earth's interior: Analysis of the global data set,…

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from article Chamois

Alpine chamois (Rupicapra rupicapra). (Photograph courtesy of Brent Huffman/Ultimate Ungulate Images)

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from article Environmental management

Environmental management seeks to provide solutions to the practical problems that humans encounter or create, including the production of garbage and waste. (Credit: Walter Zerla/Getty Images)

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from article Environmental management

Without proper environmental management, economic and industrial development often lead to environmental pollution, especially in urban environments. (Credit: Simon Alvinge/123RF)

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from article Chicxulub impact crater

Bouguer gravity anomaly map over the Chicxulub impact crater. The coastline is designated by a thin white line, cenotes (natural pits) and sinkholes are designated by black dots, and the city of Mérida and the town of Chicxulub Puerto are designated…

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from article Chicxulub impact crater

Seismic line imaging of what lies beneath the seafloor, showing the Chicxulub impact crater. The crater includes many faults that can be grouped into an exterior ring fault, a series of outer ring faults, and a series of inner ring faults. Within…

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from article Bioassay

In conducting bioassays, researchers often employ laboratory culture tests, which use, for example, bacteria cultured in a petri dish (usually to model an effect on the organism of interest or on some basic cellular function). (Credit:…

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from article Amniota

Basic types of vertebrate eggs.

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from article Amniota

Embryo developing in amniote eggs.

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from article Mecoptera

Male scorpion fly (Panorpa), order Mecoptera.

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from article Marine ecology

Marine ecology investigates the basic structural and functional relationships within and among living populations and their physical–chemical environments in marine ecosystems. In this photograph, a cold water reef in California is host to a…

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from article Marine ecology

The snaking waterways of a mangrove estuary in northwestern Madagascar. (Credit: Michael Fay/Getty Images/National Geographic RF)

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from article Marine ecology

Estuary salt marshes in the Grand Bay National Estuarine Research Reserve, Mississippi. (Credit: P. R. Hoar/National Oceanic and Atmospheric Administration)

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from article Marine ecology

Coral bleaching in the lagoon of Huahine Island, French Polynesia. Coral bleaching is the response of corals to environmental stress in which they eject the single-cell algae that live within the transparent coral tissue, making the white coral…

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from article Dental caries

The disease of dental caries or tooth decay is largely preventable. Bacteria colonize the tooth surface and often produce sufficient acids to demineralize the tooth's enamel. Then, dental plaque can build up on the tooth's surface, creating…

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from article Dental caries

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from article Swamp, marsh, and bog

Young cypress trees growing out of a swamp located in the Florida Everglades. (Credit: Getty Images)

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from article Medical control systems

Diagram of selected portions of the human motor control system. (After G. L. Gottlieb, D. M. Corcos, and G. C. Agarwal, Strategies for the control of voluntary movements with one mechanical degree of freedom, Behav. Brain Sci., 12:189–250, 1989)

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from article Medical control systems

Electric hand, a myoelectric prosthesis. (a) Two views of the hand, 2.5 in. (6 cm) across the knuckles, with the cover removed in one view to show the electric motor drive circuit. (b) Child using the electric hand. (Hugh Steeper Ltd.)

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from article Medical control systems

Hybrid control system using both functional electrical stimulation and orthoses. (a) Hierarchical control scheme. (b) Braces in use. (c) Detail of leg brace. (After Y. Kim and F. A. Spelman, eds., Images of the Twenty-First Century: Proceedings of…

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from article Medical control systems

Autoclavable pacemaker with a lithium silver vanadium pentoxide battery. (After W. Greatbatch, Pacemaker power sources, IEEE Eng. Med. Biol. Mag., 3(2):15–19, June 1984)

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from article Medical control systems

Automatic implantable cardioverter defibrillator (AICD) system with pulse generator, leads, and external programmer. (S. Nisam, Cardiac Pacemakers, Inc.)

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from article Plant vulnerability to climate change

Subarctic tundra and vegetation of the Denali National Park and Preserve in Alaska. As a result of climate change and the resultant poleward and upward shift of plant ranges, plants and their ecosystems may become particularly vulnerable. (Credit:…

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from article Plant vulnerability to climate change

Blue grama (Bouteloua gracilis) growing in Montana. As a result of warming temperatures, this type of grass could face decreased productivity, allowing forbs to increase and making the ecosystem less tolerant of drought and grazing. (Credit: Matt…

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from article Plant vulnerability to climate change

Modeled distribution of suitable climate space in Europe for stiff sedge (Carex bigelowii), which is an Arctic-Alpine plant: (a) during the period 1961–1990 (green color = suitable climate space during the 1961–1990 period); (b) climate model…

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from article Plant vulnerability to climate change

The endangered western prairie fringed orchid (Platanthera praeclara) is declining across much of its range in North America. (Credit: U.S. Fish and Wildlife Service)

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from article Geologic time scale

Geologic time scale. CLICK on image to enlarge. (Credit: International Commission on Stratigraphy, 2022)

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from article Geophysical exploration

Bouguer gravity of a portion of the Perth Basin, Western Australia. Contour interval is 1 milliGal; datum is arbitrary. Departures from regularity are called anomalies. The bulge A results from an uplift area, the contour offset along BB′ is an…

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from article Geophysical exploration

Variation of shape measurements across an anomaly. Among the shape factors sometimes measured are A, the distance over which the slope is maximum; B, the distance between points where the slope is half of the maximum slope; C, half the width of the…

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from article Geophysical exploration

Bending of seismic waves at interface; V2 > V1.

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from article Geophysical exploration

Wavefronts become more widely spaced and ray paths become curved as velocity increases with depth.

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from article Geophysical exploration

Measuring reflected seismic wave energy. (a) Dipping reflector. (b) Flat reflector.

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from article Geophysical exploration

Refractive seismic exploration data. (a) Section through model of layered earth. Curves (wavefronts) indicate location of seismic energy at successive times after a shot at A. Beyond B, energy traveling in the second layer arrives first; beyond C,…

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from article Geophysical exploration

Reflection of seismic energy obtained from reflection point R (common midpoint) by positioning a source at A and a detector at A′. The same point is involved with a source at B and a detector at B′, or C and C′. The redundancy in measuring…

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from article Geophysical exploration

Seismic surveying at sea is done by towing a long streamer containing detectors that sense seismic energy. Seismic energy is generated by several air guns that are also towed from the ship.

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from article Geophysical exploration

Seismic record section from the North Sea. The layer from about 2 to 2.3 s at the right edge is composed primarily of salt that has undergone plastic flow. The folding of the rock formations is attributed to this salt movement. The upfolding (an…

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from article Microbiome

Profile of the human microbiome by anatomical niche. DNA sequence analysis reveals the relative abundances of the six most abundant bacterial phyla in the human body. The phyla shown represent 99.6% of the sequences sampled. Cyanobacteria were…

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from article Microbiome

Cup-and-ball diagrams to conceptualize the ecosystem equilibrium of the microbiota. (a) A diverse microbial ecosystem requires a large amount of applied force (blue arrow; for example, an antibiotic disturbance) to push it out of its stable…

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from article Acquired immune deficiency syndrome (AIDS)

HIV targets helper T lymphocytes. This illustration shows HIV cells attaching to CD4 coreceptors on a helper T lymphocyte. The depletion of these helper T lymphocytes leads to acquired immune deficiency syndrome (AIDS). (Copyright © McGraw Hill)

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from article Acquired immune deficiency syndrome (AIDS)

Scanning electron micrograph of HIV-1 virions budding from a cultured lymphocyte. Multiple round bumps on the cell surface represent sites of assembly and budding of virions (green spheres). (Credit: C. Goldsmith/Centers for Disease Control and…

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from article Saccopharyngiformes

Pelican or gulper eel (Eurypharynx pelecanoides), a member of the order Saccopharyngiformes. [Photo by Alexei Orlov, Russian Federal Research Institute of Fisheries and Oceanography (VNIRO), Moscow, Russia]

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from article Trauma

Traumatic injury to the head can lead to concussions. Head injuries are frequently seen in individuals who participate in contact sports, such as football. (Credit: JoeSAPhotos/Shutterstock)

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from article Wulfenite

Wulfenite. (a) Thin tabular crystals on limonite, Organ Mountains, New Mexico (American Museum of Natural History specimen). (b) Crystal habits (after C. Klein and C. S. Hurlbut, Jr., Manual of Mineralogy, 21st ed., John Wiley and Sons, 1993).

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from article Reproductive system disorders

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from article Reproductive system disorders

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from article Reproductive system disorders

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from article Reproductive system disorders

The testicles (testes), epididymis, vas deferens and seminal vesicles, prostate gland, urethra, and penis are sites affected by disorders of the human male reproductive system. (Copyright © McGraw-Hill Education)

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