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from article Red Sea

Division of the Red Sea into regions representing different stages in the formation of an ocean basin. (After F. Martinez and J. R. Cochran, Structure and tectonics of the northern Red Sea: Catching a continental margin between rifting and drifting,…

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from article Immunity

The immune response to an invading microbe can generate immunity via antibody production. Steps: (1) Antigen binds to a B cell receptor (antibody) on a B cell. (2) The B cell may also receive more information from a helper T cell about the presence…

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from article Immunity

Colored scanning electron micrograph of an activated human macrophage. Activation of macrophages is often an important aspect of the immune response. (Credit: Steve Gschmeissner/Science Photo Library/Alamy Stock Photo)

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from article Immunity

Colored scanning electron micrograph of B lymphocytes. These white blood cells are involved in the immune response. (Credit: Steve Gschmeissner/Science Photo Library/Alamy Stock Photo)

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from article Deforestation

View of an area of deforestation in Central Kalimantan, Indonesia. In this case, the land is being cleared to develop areas for intensive rice production. (Credit: Australian National University)

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from article Deforestation

The relationship between forest and nonforest (other) land. Preservation of forest lands includes reforestation and natural regeneration. However, deforestation and natural events can lead to nonforest land. Afforestation (the act or process of…

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from article Deforestation

Natural forest areas (in hectares; 1 hectare = 2.47 acres) in various climatic domains (boreal/polar, temperate, subtropical, and tropical) from 1990 to 2015. The data are derived from the Global Forest Resources Assessment 2015 by the Food and…

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from article Deforestation

Former rainforest in northern Queensland, Australia, that was deforested in the early 1900s and is now used for pasture. (Credit: Rodney Keenan)

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from article Deforestation

Aerial view of deforestation in the Amazon region of Brazil. Clearing of trees in the Amazon rainforest has resulted in the elimination of natural resources and numerous species. (Credit: Luoman/Getty Images)

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from article Basalt

Devils Postpile, Mammoth Lakes, California, United States, which formed about 82,000 years ago, is a great example of columnar basalt. (Credit: U.S. National Park Service)

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from article Basalt

Thin section of upper crust of lava about 3 cm from top; black is microcrystalline groundmass. 0.5 mm = 0.02 in.

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from article Basalt

Thin section of interior of lava shown in Fig. 1, but 7.9 m (26 ft) below the top of the flow. Clear plagioclase crystals are ophitically enclosed in large pyroxene grains up to 1 mm in diameter. Crystals of black magnetite are minor. A few…

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from article Basalt

Growth of crystals as a function of temperature in basalt in Hawaiian lava. °F = (°C × 1.8) + 32.

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from article Basalt

Diagrams illustrating the compositions of basalts in terms of normative mineral formulas. Customarily, CaAl2Si2O8 (anorthite) is grouped together with NaAlSi3O8 (albite), and Fe2SiO4, FeSiO3, and CaFeSi2O6 are grouped with the corresponding Mg…

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from article Evolutionary computation

Typical flowchart for an evolutionary algorithm.

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from article Evolutionary computation

Traveling salesperson problem comprising 1000 cities. (a) Best-evolved solution after examination of 4 × 107 possible solutions. (b) Rate of evolutionary optimization.

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from article Evolutionary computation

Arrangement for distributing an evolutionary algorithm across multiple processors. Each processor holds its own population that undergoes random variation and selection. Occasionally, solutions will migrate from one population to another and begin…

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from article Symphyla

Scutigerella immaculata. This symphylan is a garden and greenhouse pest. (Photo by Ivo Antušek; BioLib.cz)

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from article Symphyla

Cercus (enlarged view). (Courtesy of Robert T. Allen, Academy of Natural Sciences, Philadelphia; Amanda Lawrence, Electron Microscope Center, Mississippi State University)

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from article Cestida

Structure of Cestum veneris.

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from article Ordovician

Ordovician, the second period of the Paleozoic Era.

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from article Ordovician

Early Ordovician (Arenig) paleogeography, major rock suites and potential ocean surface currents; based on remanent magnetism data supplemented by plots of the positions of shelf sea carbonates and reefs.

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from article Soil chemistry

Proper soil chemistry helps a green seedling to sprout out from the soil. Soil chemistry controls the availability of plant nutrients within the soil and thus influences plant growth. (Credit: amenic181/Shutterstock)

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from article Soil chemistry

Extensive chemical weathering can remove essential minerals and elements from soil. Typically, only the most insoluble compounds remain in the soil. For example, iron oxides may persist, imparting a reddish-brown color to the soil. (Credit: Stephen…

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from article Soil chemistry

Factors influencing the chemistry of a soil solution. (Credit: Based on an original illustration created by J. F. Hodson)

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from article Walnut

Pith of two species of Juglans: (left) butternut or white walnut (J. cinerea); (right) black walnut (J. nigra). (Photo by Bill Cook, Michigan State University; Bugwood.org)

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from article Walnut

Black walnut (Juglans nigra). (Photo by D. E. Herman, North Dakota State Soil Conservation Committee, U.S. Department of Agriculture–Natural Resources Conservation Service PLANTS Database)

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from article Walnut

Fruits of black walnut (Juglans nigra). (Photo by Rob Routledge, Sault College, Sault Ste. Marie, Ontario, Canada; Bugwood.org)

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from article Walnut

English or Persian walnut (Juglans regia). (Photo by Milan Kořínek)

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from article Walnut

Kernel of English walnut (Juglans regia). (Photo by Piero Amorati, IC Croce, Casalecchio di Reno, Italy; Bugwood.org)

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from article Walnut

Walnut leaf showing symptoms of anthracnose (caused by the fungus Gnomonia leptostyla). (Photo by Pavel Šinkyřík, Czech Republic)

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from article Walnut

Canker disease (caused by the fungus Sirococcus clavigignenti-juglandacearum) on a butternut (Juglans cinerea). (Photo by Mike Ostry, U.S. Department of Agriculture Forest Service)

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from article Lipidomics

Components of phosphoinositides. (a) General structure of phospholipids, showing positions sn-1 and sn-2, where various fatty acids may attach. X represents a phosphate-linked group; FA represents a fatty acid. (b) Space-filling models of four…

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from article Lipidomics

Selected MS ion chromatograms of synthetic 1,2-diacyl-sn-3-glycerol (DAG) molecular species from polymorphonuclear neutrophilic leukocytes (PMNs) of patients with local aggressive periodontal disease. DAG species were resolved and identified by…

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from article Lipidomics

Families of bioactive lipids. (a) Arachidonic acid is the precursor for many of the known bioactive mediators, such as EETs, prostaglandins, leukotrienes, and lipoxins. (b) Eicosapentanoic acids (C20:5 and C22:6) are precursors to potent new…

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from article Lipidomics

Functional-mediator lipidomics approach to evaluate and profile compounds during experimental inflammation and its resolution.

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from article Thrombosis

Thrombin molecular model. (Credit: Molekuul/Science Photo Library/Getty Images)

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from article Thrombosis

Organized thrombus in an artery with recanalization.

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from article Thrombosis

Organized thrombus in an artery with scar formation; the artery is completely occluded by the fibrotic mass.

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from article Cephalochordata

European lancelet (Branchiostoma lanceolatum). (After J. E. Webb, On the populations of Branchiostoma lanceolatum and their relations with the West African lancelets, Proc. Zool. Soc. Lond., 127:131, 1956)

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from article Clover

Red clover (Trifolium pratense). (Photo by Tom Heutte, U.S. Department of Agriculture Forest Service)

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from article Clover

White clover (Trifolium repens). (Photo by Pavel Šinkyřík)

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from article Clover

Crimson clover (Trifolium incarnatum). (Photo by Pavel Šinkyřík)

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from article Clover

White sweet clover (Melilotus albus). (Photo by Forest and Kim Starr)

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from article Clover

Leaves of clover affected by leaf spot, which is caused by the fungus Pseudopeziza trifolii. (Photo courtesy of the U.S. Department of Agriculture Cooperative Extension Slide Series, Clemson University)

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from article Mitochondria

A mitochondrion is a specialized compartment (organelle) of a eukaryotic cell (upper left). The electron micrograph (upper right) and the accompanying illustration (bottom) indicate the outer and inner membranes, cristae, and matrix. [Credit…

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from article Mitochondria

Three-dimensional reconstruction of a rat liver mitochondrion produced by electron microscopic tomography. During imaging, the sample is tilted around one or more axes to generate different projections that are later digitally combined to produce a…

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from article Mitochondria

Guard cells of a transgenic tobacco plant expressing green fluorescent protein (GFP) targeted to mitochondria. Chloroplasts (cell plastids) show red chlorophyll autofluorescence and mitochondria show green protein fluorescence. (Credit: Rainer…

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from article Mitochondria

Mitochondria are the powerhouses of the cell, being responsible for energy generation in the form of adenosine triphosphate (ATP). ATP is produced by the coupled processes of electron transport and oxidative phosphorylation in mitochondria.…

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from article Eye (invertebrate)

Pigment spot ocellus, the simplest invertebrate eye. (After E. E. Ruppert, R. S. Fox, and R. D. Barnes, Invertebrate Zoology: A Functional Evolutionary Approach, 7th ed., Brooks/Cole Thomson, Belmont, CA, 2004)

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from article Eye (invertebrate)

Simple open eye of the marine limpet Patella. (After E. E. Ruppert, R. S. Fox, and R. D. Barnes, Invertebrate Zoology: A Functional Evolutionary Approach, 7th ed., Brooks/Cole Thomson, Belmont, CA, 2004)

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from article Eye (invertebrate)

Large, complex eye of the marine snail Murex. (After E. E. Ruppert, R. S. Fox, and R. D. Barnes, Invertebrate Zoology: A Functional Evolutionary Approach, 7th ed., Brooks/Cole Thomson, Belmont, CA, 2004)

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from article Eye (invertebrate)

Simple pigment cup ocellus of flatworm. (After E. E. Ruppert, R. S. Fox, and R. D. Barnes, Invertebrate Zoology: A Functional Evolutionary Approach, 7th ed., Brooks/Cole Thomson, Belmont, CA, 2004)

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from article Eye (invertebrate)

Large, complex eye of the clam worm Nereis. (After E. E. Ruppert, R. S. Fox, and R. D. Barnes, Invertebrate Zoology: A Functional Evolutionary Approach, 7th ed., Brooks/Cole Thomson, Belmont, CA, 2004)

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from article Eye (invertebrate)

Simple eye of Ranzania, a marine annelid. (After E. E. Ruppert, R. S. Fox, and R. D. Barnes, Invertebrate Zoology: A Functional Evolutionary Approach, 7th ed., Brooks/Cole Thomson, Belmont, CA, 2004)

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from article Eye (invertebrate)

Highly developed eyes at anterior end of pelagic marine annelid Alciopidae. (After E. E. Ruppert, R. S. Fox, and R. D. Barnes, Invertebrate Zoology: A Functional Evolutionary Approach, 7th ed., Brooks/Cole Thomson, Belmont, CA, 2004)

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from article Eye (invertebrate)

Scallop Argopecten with one valve removed showing ocelli along the margin of the mantle. (After E. E. Ruppert, R. S. Fox, and R. D. Barnes, Invertebrate Zoology: A Functional Evolutionary Approach, 7th ed., Brooks/Cole Thomson, Belmont, CA, 2004)

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from article Eye (invertebrate)

Longitudinal section through the tubelike anterior median eye of jumping spider Salticus. (After E. E. Ruppert, R. S. Fox, and R. D. Barnes, Invertebrate Zoology: A Functional Evolutionary Approach, 7th ed., Brooks/Cole Thomson, Belmont, CA, 2004)

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from article Eye (invertebrate)

Octopus eye. (After E. E. Ruppert, R. S. Fox, and R. D. Barnes, Invertebrate Zoology: A Functional Evolutionary Approach, 7th ed., Brooks/Cole Thomson, Belmont, CA, 2004)

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from article Eye (invertebrate)

Two ommatidia from compound eye of crayfish Astacus. (After E. E. Ruppert, R. S. Fox, and R. D. Barnes, Invertebrate Zoology: A Functional Evolutionary Approach, 7th ed., Brooks/Cole Thomson, Belmont, CA, 2004)

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from article Eye (invertebrate)

Compound eye adapted for opposition image formation. Light rays from points a, b, and c. (After E. E. Ruppert, R. S. Fox, and R. D. Barnes, Invertebrate Zoology: A Functional Evolutionary Approach, 7th ed., Brooks/Cole Thomson, Belmont, CA, 2004)

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from article Eye (invertebrate)

Compound eye adapted for superposition image formation. The light from points a, b, and c is concentrated on an ommatidium. (After E. E. Ruppert, R. S. Fox, and R. D. Barnes, Invertebrate Zoology: A Functional Evolutionary Approach, 7th ed.,…

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from article Rhinoceros

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from article Ferret

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from article Siphonostomatoida

Siphonostomatoida. (a) Representative siphonostomatoid mandible; (b) brachiform maxilla (after Z. Kabata, Parasitic Copepoda of British Fishes, vol. 152, Ray Society, London, 1979). (c) Representative female caligid; (d) female Pennella (after P. A.…

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from article Holothuroidea

Cucumaria, a representative holothurian.

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from article Holothuroidea

Holothurian anatomy.

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from article Granite

Granite. (Credit: paylessimages/Getty Images)

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from article Granite

Classification of granitic rocks by the IUGS scheme. All proportions are by volume percentages.

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from article South America

Map of South America.

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from article South America

Andes Mountains, Chile. The Andes, which parallel the Pacific coast, constitute one of the Earth's most majestic features. Only the Himalayas exceed them in elevation and mass. (United Press International)

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from article South America

Representative view of the hilly uplands and low mountain country of the Guiana Highlands. One of five waterfalls on the Canaima River, Gran Sabana in southern Venezuela. (Venezuelan Information Service)

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from article South America

Uplifted beaches on desert coast, east side of San Juan Bay, Departmento de Ica, Peru. The sea cliff is about 100 ft (30 m) high. Each horizontal line represents a former beach. (Photograph by F. Atchley)

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from article South America

Port of Matarani on the desert coast of southern Peru. This oblique aerial view looks coastwise southward over one of the world's driest and most barren coastal zones. (Servicio Aerofotográfico Nacional)

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from article Sexually transmitted diseases

Acquired immune deficiency syndrome (AIDS) is a sexually transmitted disease caused by the human immunodeficiency virus (HIV). In this image, a human T cell (blue) is under attack by HIV (yellow), hampering the effectiveness of the body's immune…

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from article Sexually transmitted diseases

Prevalence of Chlamydia trachomatis (the most-common sexually transmitted bacterial pathogen) among individuals aged 14 to 39. The prevalence varies by sex, race/ethnicity, and age. Error bars indicate 95% confidence intervals. (Credit: U.S. Centers…

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from article Sexually transmitted diseases

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from article Bytownite

Bytownite, from Crystal Bay, Minnesota. (Specimen from Department of Geology, Bryn Mawr College)

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from article Calanoida

Diaptomus. (a) Lateral view of male. (b) Dorsal view of female.

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from article Excretion

Annelids (segmented worms) possess small independent nephridia. These excretory structures enable worms (as well as many other animals) to become less dependent on the immediate environment in which they live. (Copyright © McGraw Hill)

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from article Excretion

Sequence of breakdown from a nucleic acid to ammonia (NH3). Reverse pathways (broken-line arrows) indicate either a lack of knowledge of the mechanism or that other enzymes are involved. (Credit: M. Florkin)

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from article Ophiuroidea

Representative ophiuroids, which have a quite distinctive shape. (a) Ophiopeza cylindrica (alternatively, Pectinura cylindrica). (b) Asteroporpa australiensis (alternatively, Astroporpa wilsoni). (c) Gorgonocephalus chilensis.

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from article Ophiuroidea

External features of the ophiuroid Amphiura. (a) Aboral view. (b) Adoral view.

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from article Tetanus

Photomicrograph showing endospores forming at the ends of Clostridium tetani bacterial cells, which are shaped like small tennis rackets. Clostridium tetani is the causative agent of tetanus. (Credit: Lisa Burgess; copyright © McGraw Hill)

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from article Syphilis

Syphilis is caused by Treponema pallidum, which is a corkscrew-shaped motile bacterium (spirochete). (Credit: National Institute of Allergy and Infectious Diseases, National Institutes of Health)

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from article Malacostraca

Caridoid facies. (After E. R. Lankester, ed., A Treatise on Zoology, pt. 7, fasc. 3, A. and C. Black, 1909)

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from article Malacostraca

Representative malacostracan thoracic appendages: (a) biramous ambulatory thoracic appendage of an Anaspidacea; (b) uniramous thoracic walking leg of a Stenopodidea; (c) first maxilliped of a Paguroidea; (d) third maxilliped of a Thalassinoidea; (e)…

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from article Ornamental plant

Colorful ornamental plants in a garden. (Credit: Getty Images/iStockphoto)

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from article Pauropoda

A typical pauropod (genus Allopauropus) with bifurcate antennae, 9 pairs of legs, and a well-developed anal pygidium. The anterior part of the animal is located toward the top right-hand corner of the image. (Photo by Andy Murray)

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from article Rabies

Negri bodies (cytoplasmic inclusion bodies) in infected nerve cells in a dog brain are characteristic cellular changes that occur as a result of rabies encephalitis. (Credit: G. Heid/Centers for Disease Control and Prevention)

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from article Rabies

Schematic model of a rabies virus showing the surface glycoprotein spikes (projections) extending from the lipid envelope that surrounds the internal nucleocapsid and the matrix protein lining the envelope. The nucleocapsid comprises the single RNA…

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from article Monogenea

Two Monopisthocotylea (a, b) and two Polyopisthocotylea (c, d). From left to right: Pseudohaliotrema carbunculus, Heterocotyle aetobatis, Heteronchocotyle leucas, and Heteraxinoides xanthophilis.

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from article Monogenea

Life cycles of Monogenea. From left to right: (a) Gyrodactylus funduli (note embryos within embryos), (b) Polystoma integerrimum (note two types of adults either on the gills and skin of tadpoles or in the bladder), and (c) Diplozoon species (note…

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from article Metamorphic rock

Gneiss. Most gneisses are formed by recrystallization of preexisting rock during metamorphism. Shear stress present during such metamorphism causes the formation of banding. (Credit: Tyler Boyes/Getty Images)

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from article Metamorphic rock

Fabrics of metamorphic rocks under microscope. (a) Mortar fabric; (b) flaser or mylonitic fabric; (c) granoblastic fabric. (d) Lepidoblastic fabric; (e) nematoblastic fabric; (f) porphyroblast with reaction rim.

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from article Metamorphic rock

Diagram showing the general relationship between deformation folding and slaty cleavage caused by pressure PP or the couple ScSc. Heavy black lines denote the original bedding deformed into folds. Thin lines indicate slaty cleavage which may grow…

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from article Metamorphic rock

Mineral facies groups of regional metamorphic rocks showing the temperature and pressure of metamorphism. °F = (°C × 1.8) + 32.1 km = 0.6 mi.

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from article Geographic information system

Comparison of (a) raster and (b) vector data models at the boundary of a residential housing subdivision. Raster data files consist of rows of uniform cells coded according to data values. Raster files are easily manipulated, but are less detailed…

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from article Geographic information system

Overlay analysis using raster data files.

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from article Forensic palynology

Confocal image: (a) Artemisia dracunculus (sagebrush, 26 μm). Scanning electron micrographs of pollen grains: (b) Brazoria pulcherrima (mint, 26 μm); (c) Cannabis sativa (marijuana, 21 μm). Confocal image: (d) Festuca pratensis, (meadow fescue, 30…

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