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from article Perception

Perception encompasses recognition in response to sensory stimuli. Stimulation of the body's receptor organs is transformed into neural activity and is relayed to more central regions of the nervous system. Then, further neural processing occurs,…

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from article Perception

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from article Perception

Perceptual organization. (a) The figure of a four (4) is immediately and spontaneously perceived, despite the presence of other overlapping and adjacent lines. (b) The four, although physically present, is not spontaneously perceived and is even…

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from article Perception

Transposition of form; the two shapes look the same despite the difference in size.

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from article Perception

This figure is not recognizable. If, however, it is tilted 90° clockwise, it will be recognized as an outline map of Africa.

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from article Perception

Geometrical illusions. (a) The Ponzo illusion in which the two horizontal lines of equal length appear unequal. (b) The Poggendorff illusion in which the two oblique line segments are aligned with one another (that is, are collinear), but appear to…

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from article Derris

Derris elliptica. (Photo courtesy of Forest and Kim Starr)

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from article Optical coherence tomography

Typical optical coherence tomography system, based on a broadband source and fiber-optic Michelson interferometer.

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from article Optical coherence tomography

Optical coherence tomography images of healthy hamster skin in vivo. (a) Conventional magnitude image. Various layers of skin can be seen in cross section. (b) Result after Doppler processing of the same signal used to create the magnitude image.…

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from article Adenosine triphosphate (ATP)

Structure of adenosine triphosphate (ATP), which consists of ribose, adenine, and a triphosphate group (a chain of three phosphate groups, designated α, β, and γ). The structures of adenosine diphosphate (ADP), adenosine monophosphate (AMP), and…

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from article Adenosine triphosphate (ATP)

The ATP cycle, in which ATP is converted to ADP and phosphate (P), which is a process that creates energy for endergonic (energy-absorbing) reactions (for example, protein synthesis and muscle contraction); then, ADP is phosphorylated and converted…

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from article Homeostasis

Homeostasis in living organisms is a self-regulating process that ensures the stability of biological systems needed for survival. With the help of receptors, the brain (a type of control center) detects the difference from the "set point" and…

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from article Poppy

Stems, fruits (capsules), and flower of the opium poppy (Papaver somniferum). By cutting into the fruits soon after the petals have fallen, the opium is obtained. (Credit: Milan Kořínek)

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from article Sarcomastigophora

An opalinid (Protoopalina axonucleata) showing primary and secondary lines of blepharoplasts.

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from article Sarcomastigophora

Hedriocystis reticulata, a small heliozoan of the superclass Sarcodina.

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from article Sarcomastigophora

A xylophagous symbiotic flagellate (Trichonympha sp.) from a termite.

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from article Kinorhyncha

Echinoderes sp., a cyclorhagid kinorhynch (ventrolateral view).

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from article Synthetic immunology

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from article Bioremediation

Contaminating oil spill on the surface of ocean water. (Credit: Steve Martarano/U.S. Fish and Wildlife Service)

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from article Bioremediation

Controlled oil burns were used to reduce the amount of surface oil following the Deepwater Horizon explosion in the Gulf of Mexico in 2010. (Credit: John Masson/U.S. Coast Guard)

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from article Bioremediation

Diagram of in situ bioremediation. Microorganisms and nutrients are introduced into the site, where they flow into the area containing pollutants. The bioremediation process is monitored, and water and by-products are extracted using wells. (Credit:…

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from article Plant pigment

Photosynthetic spectra of higher plants. (Left) Absorption spectra for chlorophyll a, chlorophyll b, and the carotenoids, showing the wavelengths of visible light that support photosynthesis. (Right) Action spectrum for photosynthesis. (Copyright ©…

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from article Plant pigment

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from article Plant pigment

The autumn colors of leaves are produced by carotenoid pigments. During the autumn, leaves stop their production of chlorophyll, providing the opportunity for the orange and yellow carotenoid colors observed in autumn leaves to predominate. In…

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from article Plant pigment

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from article Cytoskeleton

Two interphase cells with immunofluorescence labeling of actin filaments (bluish purple), microtubules (yellow), and nuclei (turquoise). (Credit: Torsten Wittmann/Scripps Research Institute)

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from article Cytoskeleton

Endothelial cells from a cow lung showing two components of the cytoskeleton: actin filaments (orange/red) and microtubules (green). (Credit: Tina Carvalho)

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from article Cytomegalovirus infection

Photomicrograph of three enlarged cells with large intranuclear inclusions (each with a clear peripheral halo), which are characteristic of cytomegalovirus infection. In this particular case of an immunosuppressed patient, the cytomegalovirus…

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from article Cytomegalovirus infection

Cytomegalovirus virion inclusion. A transmission electron microscopic (TEM) image depicting cytomegalovirus virions (complete, mature virus particles) in an unknown tissue sample. (Credit: National Center for Immunization and Respiratory Diseases)

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from article Arthropoda

The insects are the largest group within the phylum Arthropoda. Some of the most visually appealing insects are the butterflies (order Lepidoptera). (Credit: Shutterstock)

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from article Arthropoda

Crustaceans constitute some of the most notable arthropods. The Chesapeake blue crab (Callinectes sapidus) is native to the western Atlantic Ocean and Gulf of Mexico. (Credit: Sandy Franz/Getty Images)

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from article Arthropoda

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from article Arthropoda

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from article Arthropoda

Fossil of a trilobite, showing its distinctive flattened oval shape and crosswise division of the body (into a head, a thorax, and a pygidium). (Credit: Shutterstock)

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from article Lissamphibia

Pedicellate teeth in Lissamphibia: (a) salamander; (b) apodan; (c) frog. Teeth are from the lower jaw (a, b) or upper jaw inverted (c) and are viewed from inside the mouth. (After T. Parsons and E. E. Williams, The teeth of Amphibia and their…

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from article Lissamphibia

Operculum-stapes complex of a primitive salamander (skin removed to show internal structures).

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from article Aortic body

Oval-shaped aortic bodies are found lying on the anterior and posterior surfaces of the aortic arch and pulmonary artery.

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from article Crustacea

A blue crab (Callinectes sapidus) is a common crustacean found in waters of the western Atlantic Ocean and the Gulf of Mexico. (Credit: Phil Lowe/Shutterstock)

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from article Crustacea

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from article Crustacea

Cephalic and thoracic appendages [(a–d) antennules; (e–h) mandibles; (i–l) thoracopods] of representative crustaceans: (a) Brachypoda; (b) Leptostraca; (c, d) Decapoda; (e) Brachypoda; (f) Stomatopoda; (g) Mysida; (h) Decapoda; (i) Anostraca; (j)…

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from article Crustacea

Larval stages of representative crustaceans: (a) cyprid larva of Sessilia; (b) pseudolarva of Stomatopoda; (c) phyllosoma larva of Decapoda; (d) zoeal larva of Decapoda; (e) megalopa of Decapoda. (Credit: Patsy A. McLaughlin)

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from article Glyptodont

A glyptodont skeleton belonging to the type genus, Glyptodon. (Credit: Gyik Toma)

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from article Glyptodont

Reconstruction of Glyptotherium texanum from Arizona. (Credit: David D. Gillette; illustration by Bonnie Dalzell)

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from article Glyptodont

Hexagonal osteoderm (a protective bony plate) in (top) lateral view and (bottom) external view. (Credit: David D. Gillette)

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from article Glyptodont

Cutaway interpretation of the osteology (skeletal and bone structure) of Glyptotherium. (Credit: Larry Isham)

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from article Kenaf

Harvesting of kenaf (Hibiscus cannabinus) in Texas. (Photo by David Nance, Agricultural Research Service, U.S. Department of Agriculture)

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from article Electric organ (biology)

Representative electric fishes: (a) Electrophorus; (b) Torpedo; (c) Malapterurus; (d) Astroscopus; (e) Gnathonemus; (f) Gymnarchus; (g) Raja; (h) Gymnotus; (i) Sternarchus. Electric organs are shaded or solid and indicated by small arrows.…

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from article Electric organ (biology)

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from article Electric organ (biology)

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from article Electric organ (biology)

Current flow through a single electrocyte and fields around an electric fish. (a) Cross section of a flattened cell at rest. Each face is specifically permeable to K+ and the cell interior is at a negative potential. Because equal potentials are…

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from article Electric organ (biology)

Representative electrocytes. Body axes are indicated by the arrows except that the Torpedo electrocyte is shown ventral surface up. Innervation is indicated by branching, except for Malapterurus in which a single nerve fiber makes a single contact…

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from article Electric organ (biology)

Patterns of electric organ discharge. (A) An electric catfish; potentials recorded between head and tail in a small volume of water with head negativity upward. Pulses attain a maximum frequency of 190/s. (A′) Single pulse. (B–D) Weakly electric…

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from article Gene amplification

Gene amplification occurs when the number of copies of a specific gene sequence is disproportionately increased in the parent genome. In this case, the specific gene sequence is duplicated. (Credit: Mina Kang)

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from article Gene amplification

Amplification of DNA using the polymerase chain reaction (PCR) method. After 20 cycles, the selected sequence has been amplified about 106-fold. The colored region indicates the target DNA to be amplified. The shorter arrows represent the…

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from article Gene amplification

Three mechanisms of gene amplification; n, m, and o are genes or groups of genes in the process of amplification. (a) Rolling circle: genes are copied from a single-stranded circle; they become double-stranded subsequently. (b) Multiple initiation…

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from article Chonotrichida

Spirochona, an example of a chonotrichid.

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from article Land-use planning

Land-use planning map for Tysons Corner, Virginia, showing land-use categories. [Credit: Fairfax County, Virginia (CC BY-ND 2.0)]

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from article Abaca

Abaca (Musa textilis) growing in the Philippines. (Credit: Afren de Guzman/Maitum Information Office, Sarangani, Philippines)

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from article Hardy-Weinberg formula

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from article Hardy-Weinberg formula

Application of the Hardy-Weinberg formula in the case of cystic fibrosis. There are about 100 times as many persons who are heterozygous carriers of the cystic fibrosis gene as there are persons who are homozygous for it. (Copyright © McGraw-Hill…

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from article Spitzer Space Telescope

Artist's impression of the Spitzer Space Telescope. (Credit: NASA/JPL-Caltech)

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from article Spitzer Space Telescope

The orbit of Spitzer. The Earth orbits the Sun in a counterclockwise direction in this figure, and the frame of reference rotates with the Earth-Sun line to show how Spitzer trails behind. Viewed in a solar frame of reference, the Spitzer orbit is a…

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from article Spitzer Space Telescope

Cutaway drawing of Spitzer, showing the major subsystems.

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from article Spitzer Space Telescope

Spitzer Space Telescope image of the Eagle Nebula, a star-forming region with a network of turbulent dust clouds and newborn stars about 7000 light-years away. Green denotes cooler dust fields, including the three famous "Pillars of Creation"…

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from article Spitzer Space Telescope

Spitzer Space Telescope image of the center of the Milky Way Galaxy, about 26,000 light-years distant, with hundreds of thousands of stars and a variety of dust clouds. The pictured region, about 900 light-years across, cannot be seen in visible…

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from article Plant hormone receptor

The signal transduction pathway of auxin (a notable plant hormone). Auxin/indoleacetic acid (Aux/IAA) proteins form dimers with auxin response factors (ARFs) bound to promoters of auxin-regulated genes, causing transcriptional repression. Repression…

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from article Plant hormone receptor

Gibberellin signal transduction pathway. DELLA proteins repress gibberellin (GA) response via an unknown mechanism (indicated by a question mark). Gibberellin binding to GID1 promotes interaction of GID1 with DELLA proteins. The DELLA proteins are…

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from article Branchiobdellida

Lateral view of the East Asian Cirrodrilus uchidai (Yamaguchi, 1934), showing the head with dorsal peristomial tentacles and fingerlike dorsal projections on the body segments. Scale bar = 0.2 mm (0.008 in.). [From S. R. Gelder, Observations on…

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from article Perciformes

Skeleton of a generalized perciform fish. The axial skeleton (head, vertebral column and ribs, and dorsal, anal, and caudal fins) is unshaded; the appendicular skeleton (pectoral and pelvic girdles and associated fins) is darkly shaded. (From H. T.…

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from article Perciformes

Pectoral and pelvic girdles of a generalized perciform fish. (From H. T. Boschung and R. L. Mayden, 2004)

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from article Perciformes

Striped bass (Morone saxatilis). (Photo courtesy of U.S. Environmental Protection Agency)

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from article Perciformes

Yellowspotted grouper (Epinephelus timorensis). (Photo by Richard C. Wass; Checklist of the Fishes from the National Park of American Samoa/NPS)

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from article Perciformes

Rock bass (Ambloplites rupestris). (Photo by Eric Engbretson/U.S. Fish and Wildlife Service)

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from article Perciformes

Smallmouth bass (Micropterus dolomieu). (Photo by Eric Engbretson/U.S. Fish and Wildlife Service)

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from article Perciformes

Yellow perch (Perca flavescens). (Photo by Eric Engbretson/U.S. Fish and Wildlife Service)

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from article Perciformes

Bluespotted wrasse (Anampses caeruleopunctatus). (Photo by Richard C. Wass; Checklist of the Fishes from the National Park of American Samoa/NPS)

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from article Perciformes

Searcher (Bathymaster signatus). (Photo courtesy of Jan Haaga, Kodiak Laboratory, Alaska Fisheries Science Center, National Marine Fisheries Service)

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from article Perciformes

Icefish (Chionodraco hamatus).

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from article Perciformes

Leopard (or shortbodied) blenny (Exallias brevis). (Photo courtesy of Richard C. Wass; Checklist of the Fishes from the National Park of American Samoa/NPS)

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from article Perciformes

Morrison's dragonet (Synchiropus morrisoni). (Photo courtesy of Richard C. Wass; Checklist of the Fishes from the National Park of American Samoa/NPS)

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from article Perciformes

Halfspotted goby (Asterropteryx semipunctatus). (Photo courtesy of Richard C. Wass; Checklist of the Fishes from the National Park of American Samoa/NPS)

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from article Perciformes

Whitespotted surgeonfish (Acanthurus guttatus). (Photo courtesy of Richard C. Wass; Checklist of the Fishes from the National Park of American Samoa/NPS)

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from article Perciformes

Bigeye barracuda (Sphyraena forsteri). (Photo courtesy of Richard C. Wass; Checklist of the Fishes from the National Park of American Samoa/NPS)

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from article Perciformes

Yellowfin tuna (Thunnus albacares). (Photo courtesy of Richard C. Wass; Checklist of the Fishes from the National Park of American Samoa/NPS)

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from article Terrestrial ecosystem

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from article Respiratory system disorders

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from article Respiratory system disorders

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from article Osteoporosis

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from article Osteoporosis

Decrease in bone density with age in women. Before menopause, bone loss affects primarily the spine and hip (femur and pelvis); after menopause, bone loss is most pronounced in the radius bone of the forearm.

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from article Lingulida

View of living Lingula anatina in its burrow. (Courtesy of C. C. Emig)

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from article Animal camouflage

A Vietnamese mossy frog (Theloderma corticale) uses camouflage to blend into its surroundings. (Credit: David M. Hunt/123RF)

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from article Animal camouflage

Three body pattern types—uniform, mottle, and disruptive—are universal for camouflage in the animal kingdom. These patterns have evolved in animals of every size and shape, including both invertebrates and vertebrates, and occur in aquatic and…

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from article Animal camouflage

Octopus vulgaris reacting to a diver (predator). The initial change from camouflaged to conspicuous takes only milliseconds (ms) as a result of direct neural control of the skin. Full expression of the threat display (right) is 2 s. Video frame…

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from article Animal camouflage

A visual sensorimotor assay for probing cuttlefish (Sepia officinalis) perception and subsequent dynamic camouflage. (Top) Visual backgrounds with different size, contrast, edge characteristics, and arrangement are perceived by the cuttlefish, which…

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from article Animal camouflage

Color matching of camouflaged cuttlefish when viewed by hypothetical dichromatic and trichromatic fish predators. (A) The pseudocolor image for simulating the human view of the cuttlefish at near-surface. This composite image was formed by using…

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from article Lyophilization

Apparatus for rapid high-vacuum desiccation of frozen suspensions of biologic materials. (After A. J. Salle, Fundamental Principles of Bacteriology, 4th ed., McGraw-Hill, New York, 1954)

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from article Hormone

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from article Hormone

Epinephrine (an adrenal hormone) binds to a hormone receptor in the plasma membrane of a cell, leading to a cascade of intracellular activations that regulate cell behavior. In this instance, the binding leads to activation of an enzyme that changes…

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from article Appendix (anatomy)

Junction of the human ileum and colon, showing the cecum and vermiform appendix. (From C. K. Weichert, Anatomy of the Chordates, 4th ed., McGraw-Hill, New York, 1970)

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from article Echinodermata

Cross section through the spine of an echinoid showing the microscopic structure of the skeleton. The stereom forms a continuous mesh and the stroma that secretes it lies in the interspaces which, in this case, are arranged in radial rows.

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