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from article Aspidorhynchiformes
Aspidorhynchus acutirostris, Upper Jurassic, Bavaria; a typical fish of the order Aspidorhynchiformes.
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from article Paleobotany
Compression specimen of the Triassic leaf type Dicroidium.
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from article Paleobotany
Permian pollen grain macerated from Antarctic coal.
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from article Paleobotany
Cross section of a permineralized stem from a Carboniferous coal ball.
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from article Paleobotany
Thin section of a petrified Rhynie chert stem.
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from article Paleobotany
Several coprolites found within the tissues of a Carboniferous plant.
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from article Paleobotany
Cuticle of a fossil (Eocene) leaf showing the outline of the epidermal cells and fungus with specialized hyphae.
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from article Paleobotany
Several Glossopteris leaves from the Permian of Antarctica. Leaves of this type were some of the first evidence that at one time the southern continents were all physically linked into a major continental plate called Gondwana.
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from article Paleobotany
Section showing tree rings from a temperate plant, showing change in cell size and wall thickness.
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from article Paleobotany
Section showing rings from a tree with uniform cell size and wall thickness, but growing at approximately 82° South during the Triassic.
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from article Osteolepiformes
Schematic phylogeny (family tree) of the osteolepiforms, based on arguments presented by P. Ahlberg and Z. Johanson (1998). The fishes within the gray zone are conventionally designated as Osteolepiformes (the formal group name), but they actually…
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from article Osteolepiformes
The tristichopterid Eusthenopteron foordi. (a) A close-up of its pectoral fin skeleton. (b) An illustration of the full specimen. Eusthenopteron reached approximately 50–70 cm in length. Its pectoral fin skeleton contains structures equivalent to…
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from article Parasympathetic nervous system
Overview of parasympathetic pathways of the human autonomic nervous system. Preganglionic axons from the brain and spinal cord innervate the viscera in the head, neck, and trunk. (Copyright © McGraw Hill)
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from article Fertilization (animal)
Photomicrograph (tinted green) of mouse sperm bound to the zona pellucida of an unfertilized egg under laboratory conditions (in vitro). (Credit: K. O. Kalthoff)
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from article Fertilization (animal)
Mammalian sperm (a) adhering to the zona pellucida, (b, c) undergoing the acrosome reaction, and (c, d) penetrating the zona pellucida on its way to the egg cell proper. (Copyright © McGraw Hill)
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from article Chemical senses
The sense of smell (olfaction) is a key chemical sense in vertebrates. (Left) Taste buds of the oral cavity, especially the tongue, are composed of modified epithelial cells responsive to chemicals in solution. (Right) Bitter, sour, salty, and sweet…
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from article Pigmentation
Colorful flower of Mirabilis jalapa. The colors of the flowers of this plant can vary as a result of different plant pigments. (Credit: F. D. Richards)
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from article Pigmentation
Zebrafish are often studied as model organisms for research dealing with skin pigmentation. (Credit: Lynn Ketchum/Oregon State University)
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from article Coronoidea
Stephanocrinus gemmiformis, Middle Silurian, Tennessee; side view of the theca.
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from article Neurohypophysis hormone
Structure of neurohypophysial hormones. Each neurohypophysial hormone is made up of nine amino acid residues with two half cysteines joined by a disulfide bridge to form a ring structure. Vasotocin is found in fishes and fetal pituitaries, while…
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from article Peroxisome
Electron micrograph of a cell of Yarrowia lipolytica (a type of yeast) grown in fatty acid–containing medium. (Copyright © McGraw Hill)
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from article Bipolar disorder
Prevalence of bipolar disorder in adults. The bar graph shows the percent of the U.S. adult population affected by bipolar disorder as it relates to age. (Credit: National Institute of Mental Health)
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from article Enzyme inhibition
Enzyme inhibition often works by preventing a substrate from attaching to an active enzyme. In this example, E1 is one of three sequential enzymes that will convert a substrate (S) into a product (P). However, the product that is created can then…
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from article Enzyme inhibition
Two types of reversible enzyme inhibition. (Left) In competitive inhibition, the inhibitor interferes with the active site of the enzyme, so the substrate is unable to bind to it. (Right) In noncompetitive inhibition, the inhibitor changes the…
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from article Docodonta
Restoration of the skull of the Late Jurassic docodont Haldanodon in lateral view. Arrow points to dentary-squamosal articulation; the articular-quadrate articulation lies directly behind it (toward the midline of the skull). (Illustration by…
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from article Docodonta
Upper and lower molars of Docodon, a Late Jurassic docodont. (a) Occlusal view of an upper molar. (b) Internal and (c) occlusal views of a lower molar.
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from article Neuroeconomics
Neuroeconomics applies neuroscientific tools and methodologies to investigate the decision making that occurs inside the brain. (Credit: James Steidl/SuperStock)
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from article Alpine vegetation
A windswept and stunted whitebark pine (Pinus albicaulis) growing among the alpine vegetation on Mount Washburn in Yellowstone National Park, Wyoming, United States. (Credit: R. G. Johnsson)
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from article Alpine vegetation
Alpine vegetation and flowers blooming in Mount Rainier National Park in Washington, United States. (Credit: National Park Service)
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from article Doppler VOR
Collocation of Doppler VOR and TACAN beacons installed on 100-foot high (30-m) tower with a counterpoise of 119-ft (36-m) diameter in forest near Frankfurt, Germany. Circular array consists of 39 loop antennas fed by solid-state commutator. Center…
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from article Doppler VOR
Principle of Doppler VOR beacon. Reference signal R and bearing signal V which is generated by dipole d are shown as they would be measured in aircraft to the north, east, south, and west of the beacon. (a) Dipole d at 180°. (b) Dipole d at 270°.…
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from article Doppler VOR
Comparison of radial flight recordings. (a) From VOR installation. (b) From DVOR installation. Both experimental beacons were located at same unfavorable site. Plane is flying constant course at bearing of 133° from beacons at 4000-ft (1.2-km)…
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from article Killer whale
Killer whales (Orcinus orca) in the waters off Alaska. (Credit: David Ellifrit/Alaska Fisheries Science Center, National Oceanic and Atmospheric Administration)
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from article Killer whale
The tail of a killer whale. (Credit: Janice Waite/Alaska Fisheries Science Center, National Oceanic and Atmospheric Administration)
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from article Lysosome-related organelle
Recruitment of cargo molecules into protein-coated (clathrin-coated) vesicles at the trans-Golgi network (TGN) for delivery to incipient lysosomes or lysosome-related organelles. In the TGN, soluble lysosomal or lysosome-related organellar proteins…
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from article Paleopathology
The fused spine and ribs in a case of ankylosing spondylitis from an adult male human found at a burial site near the Kuskokwim River, Alaska. (Credit: Department of Anthropology, National Museum of Natural History, Smithsonian Institution Catalog…
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from article Paleopathology
Pottery figurine of an achondroplastic dwarf from an archeological site in Tachina, Esmeraldas, Ecuador, dated between 500 BCE and 500 CE. (Credit: Department of Anthropology, National Museum of Natural History, Smithsonian Institution Catalog No.…
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from article Paleopathology
Sword trauma that removed part of the left upper jaw and the right lower jaw so that no remaining teeth were in contact between the jaws. The adult male human survived this injury. The skull is from an archeological burial site near the Stewart…
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from article Paleopathology
Destruction of the lower portion of the fourth lumbar vertebra (arrow), probably caused by tuberculosis, from a young male human skeleton found at the archeological burial site of Bâb edh-Dhrâ in Jordan, dated to approximately 3300 BCE. (Credit:…
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from article Paleopathology
The effect of scurvy on the right side of the cranium of an 11-year-old human child from the archeological site of Pachacamac, Peru. (Credit: Department of Anthropology, National Museum of Natural History, Smithsonian Institution Catalog No. 266599)
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from article Psychological resilience
Psychological resilience refers to positive adaptation among individuals at risk for maladjustment. There are three classes of protective factors that help people to thrive in the face of significant adversities: support from close family and…
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from article Psychological resilience
The strongest predictor of resilient adaptation is the quality of an individual's close, personal relationships. In general, positive relationships help individuals to combat adversity through collective problem solving and through the sharing of…
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from article Suicide
Methods of suicide in (left) males and (right) females. The three most prevalent methods of suicide involve firearms, suffocation, and poisoning. Males are much more likely to use firearms, whereas the preferred method in females is poisoning.…
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from article Suicide
Age-adjusted suicide rates in males and females from 1999 to 2017 in the United States. (Credit: National Vital Statistics System, National Center for Health Statistics, Centers for Disease Control and Prevention)
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from article Gastrointestinal tract disorders
The major organs and associated anatomical structures of the gastrointestinal tract. (Copyright © McGraw-Hill Education)
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from article Gastrointestinal tract disorders
A cross section of a peptic ulcer, illustrating the four layers: fibrin (black arrowhead), neutrophils (black arrow), granulation tissue (white arrowhead), and fibrosis (white arrow). (Copyright © McGraw-Hill Education)
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from article Gastrointestinal tract disorders
Small intestine biopsy showing villous atrophy, which is found in individuals affected by celiac disease. (Credit: Ed Uthman/National Institutes of Health)
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from article Lepisosteiformes
Spotted gar (Lepisosteus oculatus). (Photo by Brian Montague, U.S. Fish and Wildlife Service)
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from article Extremophile
Extremophile (psychrophile) bacteria (Carnobacterium pleistocenium) retrieved from the ice of a frozen Alaskan pond dating back approximately 32,000 years. (Credit: Marshall Space Flight Center, National Aeronautics and Space Administration)
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from article Tommotian fauna
Tube-dwelling animals of the Tommotian fauna. (a) Cloudina, one of the earliest animals with a mineralized skeleton. (b) Aculeochrea, an anabaritid showing the three-rayed symmetry typical of the group. (c) Hyolithellus, an animal reinforcing its…
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from article Tommotian fauna
Reconstruction of life cycle of the probably scyphozoan Olivooides, based on fossilized embryos and polyps.
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from article Tommotian fauna
An archaeocyathan, interpreted to be a calcareous sponge.
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from article Tommotian fauna
Sclerite-bearing animals and probably mollusks. (a) Halkieria, a scale-and-plate-clad coeloscleritophoran (reprinted with permission from M. S. Conway and J. S. Peel, Articulated halkieriids from the Lower Cambrian of north Greenland, Nature,…
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from article Mouth disorders
Stages involved in the formation of periodontitis: (left) normal, nondiseased state of teeth, bone, and the gingiva (gum tissue); (middle) calculus buildup and early gingivitis (inflammation of the gums); (right) late-stage periodontitis, with…
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from article Trilobita
Two iron-stained trilobites (Paradoxides) on a bedding plane slab from Morocco, North Africa, of Cambrian age. (Credit: Alan Morgan)
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from article Trilobita
Trilobite diversity and preservation. (a) Olenellid, Lower Cambrian (British Columbia). External mold of exoskeleton in shale. (b) Ogygopsis, Middle Cambrian (British Columbia). Molt assemblage, with cranidium and pygidium aligned, but librigenae,…
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from article Trilobita
Morphological features of trilobites. (a) Calymene, Silurian (New York). Dorsal view of mineralized exoskeleton. (b) Phacops, Devonian (Ohio). Ventral (bottom) view of cephalon and anterior segments of the thorax, with hypostome attached. (c)…
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from article Trilobita
Triarthrus eatoni, Upper Ordovician (New York). Reconstruction with dorsal exoskeleton removed on right side to show appendages. Antennae are incomplete. Exites (gill branches) of the first nine postantennal appendages are removed to show the…
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from article Fate maps (embryology)
Principle of fate mapping. (a) Label placed in a certain position on the egg ends up in a reproducible position on the later animal. (b) Possible fate map for this type of egg. (Reprinted with permission from J. M. W. Slack, Essential Developmental…
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from article Fate maps (embryology)
Fate maps of urodele blastula from (a) lateral and (b) dorsal aspects, deduced from vital staining. (After J. M. W. Slack, From Egg to Embryo: Determinative Events in Early Development, Cambridge University Press, 1983)
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from article Fate maps (embryology)
Fate map of the Arabidopsis embryo. (a) Heart stage embryo. (b) Mature embryo. (c) Seedling. The embryo is delineated into sectors from an early heart stage to give rise to specific regions or tissue types. The apical region (large shaded areas in…
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from article Fate maps (embryology)
Image of an Arabidopsis root tip (confocal micrograph). The root morphology is revealed by counterstaining with propidium iodide. The nuclei marked by fluorescent marker (circles at left) represent cells derived from a single initial/progenitor cell…
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from article Forest fire
Exclusion of fire by humans has contributed to dramatic large blazes in the western United States. (Credit: Kari Greer)
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from article Forest fire
Crown fire in northern California. (Credit: Kari Greer)
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from article Forest fire
Values at risk during a forest fire can vary, depending on the location of the fire. (Credit: USDA Forest Service)
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from article Forest fire
Wildland firefighters work to separate the fuels on the ground from the fire in an effort to stop the spread of the fire. (Credit: Kari Greer)
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from article Forest fire
Engine crews work to suppress a large wildfire in northern California. (Credit: Kari Greer)
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from article Forest fire
Mega-fires often result in severe damage to natural resources and have long-lasting regional impacts. (Credit: USDA Forest Service)
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from article Forest fire
An example of fire prevention education: Smokey Bear. (Credit: USDA Forest Service)
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from article Forest fire
Lookouts in places where elevation and vision allow for a wide view of a broad expanse play an integral role in fire detection. (Credit: Kari Greer)
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from article Forest fire
Through a variety of management activities, societies seek to mitigate the impacts of wildfire. (A) Use of a masticator to reduce fuels. (B) Use of a low-intensity, prescribed (planned) fire to reduce the density of the vegetation, reduce fuels, and…
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from article Forest fire
Methods of fire suppression include hand crews, engine crews, and airborne intervention. While aircraft support firefighting efforts, forest fires are extinguished by ground-based firefighters. (Credit: USDA Forest Service)
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from article Forest fire
Extremely intense, fast moving forest fires can overwhelm even the most experienced, well-equipped firefighting workforce. (Credit: USDA Forest Service)
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from article Radiation injury to plants and animals
The total range of wavelengths and frequencies of electromagnetic radiation, extending from the longest radio waves to the shortest known cosmic rays. In general, exposure to electromagnetic radiation can be injurious to living matter, resulting in…
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from article Radiation injury to plants and animals
Thirty-day mortality of mice exposed acutely to fast neutrons, x-rays, and gamma rays. (Credit: A. C. Upton)
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from article Radiation injury to plants and animals
Squamous cell carcinoma is one of the most common forms of human skin cancer and is often caused by exposure to various forms of ionizing or ultraviolet radiation. (Copyright © McGraw-Hill Education)
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from article Transposable elements
Transposable elements are mobile and can move from one position to another in the genome. Typically, DNA strands are cut by a transposase, and the transposable elements are incorporated elsewhere in the genome. The mechanism can involve duplications…
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from article Transposable elements
Structure of the major transposable element groups. Labeled rectangles represent gene sequences, and horizontal lines indicate noncoding portions of the transposable element (these are not drawn to scale; also note that many transposable elements…
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from article Thymus gland
Thymus of a 3-month-old human infant. Histological section through a portion of one lobe.
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from article Plants of saline environments
Desert arrowweed (Pluchea sericea) is a halophytic evergreen shrub adapted for growth in the salty basins of Death Valley, California. (Credit: Steven P. Lynch)
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from article Plants of saline environments
Soluble salts in irrigation water and those present in fertilizers lead to the gradual accumulation of toxic levels of sodium ions in topsoil, rendering the land useless. (Credit: Roberto A. Gaxiola)
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from article Plants of saline environments
Relationship between growth and sodium chloride concentration for halophytes and glycophytes. The diagram assumes that the plants are growing in a culture solution that accounts for about 10–20 mol m−3 of ions. (Copyright © McGraw Hill)
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from article Plants of saline environments
Suaeda maritima (annual sea blite), a halophytic member of the Chenopodiaceae. (Credit: František Pleva)
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from article Plants of saline environments
Gray mangrove (Avicennia marina) on the island of Tonga. Aerial roots called pneumatophores, which act as a snorkel, are growing out of the mud. Other mangroves can absorb air through holes in their bark known as lenticels. (Credit: Valentina…
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from article Plants of saline environments
Salt gland from the mangrove swamp species Aegiceras corniculatum. (a) Secretory cells surrounded by cuticle and epidermal cells. (b) Section through the gland. (Copyright © McGraw Hill)
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from article Monoplacophora
Living and fossil Monoplacophora. (a) Neopilina galatheae. (b) Tryblidium reticulatum. (After R. C. Moore, ed., Treatise on Invertebrate Paleontology, pt. I, 1957)
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from article Monoplacophora
Side views of various helcionellacean and bellerophont univalved mollusks. (a) Cyrtonellopsis; (b) Hypseloconus; (c) Cyclocyrtonella; (d) Stenotheca; (e) Bellerophon; (f) Tropidodiscus. (After B. Runnegar, Class Monoplacophora, in R. S. Boardman, A.…
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from article Cell (biology)
A typical structure of a prokaryotic (bacterial) cell. (Copyright © McGraw-Hill Education)
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from article Cell (biology)
Animal cell structure and anatomy. A term with an asterisk indicates that the structure is not found in plant cells. (Copyright © McGraw-Hill Education)
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from article Cell (biology)
Plant cell structure and anatomy. A term with an asterisk indicates that the structure is not found in animal cells. (Copyright © McGraw-Hill Education)
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from article Gorgonacea
Gorgonian colonies in life. (a) Plumigorgia cf. hydroides, Palawan, Philippines. (b) Eunicella gracilis, São Tomé, Gulf of Guinea. (c) Junceella fragilis, Luzon, Philippines. (d) Leptogorgia alba, Cocos Island, Costa Rica. (e) Astrogorgia sp.,…
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from article Gorgonacea
Some common gorgonaceans. (a) Thouarella hicksoni (inset, detail of polyps). (b) Ideogorgia capensis. (c) Eunicella papillosa. (d) Leptogorgia lutkeni. (e) Junceella sp. (f) Anthothela parviflora. (g) Rumphella sp. (h) Homophyton verrucosum. (i)…
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from article Gorgonacea
Gorgonian colonies (dry preserved specimens). (a) Briareum sp. (b) Ideogorgia capensis. (c) Chrysogorgia pinnata. (d) Fanellia compressa. (e) Viminella sp. (f) Paragorgia sp. (g) Subergorgia suberosa. (h) Isis hippuris. (i) Solenocaulon sp.
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from article Gorgonacea
Caribbean gorgonian colonies (digital scans from dry preserved specimens). (a) Muricea cf. fruticosa. (b) Gorgonia ventalina. (c) Pseudopterogorgia cf. hummelincki.
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from article Gorgonacea
Gorgonian colonies (dry preserved specimens). (a) Leptogorgia palma. (b) Skeleton of Isidella sp. (Artwork courtesy of Jessica Machnicki, California Academy of Sciences)
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from article Gorgonacea
Gorgonian morphology.
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from article Inertial navigation system
Elementary accelerometer.
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from article Inertial navigation system
Computation of distance by two integrations. Integration of acceleration gives velocity; integration of velocity gives distance.
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from article Inertial navigation system
Schematic of a three-gimbal platform.
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from article Inertial navigation system
Strap-down inertial navigation system. (After A. Lawrence, Modern Inertial Technology, 2d ed., Springer, New York, 1998)
