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from article Marjoram
Close-up view of marjoram (Majorana hortensis; alternatively Origanum majorana). (Photo courtesy of Forest and Kim Starr)
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from article Stress (psychology)
Dimensions of stressful experiences. (Image courtesy of the National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health)
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from article Stress (psychology)
Diagram of the hypothalamic-pituitary-adrenal axis. The thicker arrow indicates that the feedback of glucocorticoids on ACTH is most potent. Abbreviations: ACTH, adrenocorticotropic hormone; CRH, corticotropin-releasing hormone.
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from article Tooth
Stages in the development of a tooth.
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from article Tooth
Schema showing tooth replacement in lower vertebrates. (a, b) Horizontal lines represent the strand of tissue which connects the tooth germs in most vertebrates; vertical lines indicate the distance from the tooth germs to the surface of the jaw. In…
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from article Bioterrorism
Civilians are the prime targets in bioterrorist attacks. During World War II, gas masks with filters were distributed to British civilians because of fears of a chemical agent attack. (Credit: Ingram Publishing/SuperStock)
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from article Bioterrorism
A color-enhanced scanning electron micrograph (SEM) 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…
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from article Chestnut
American chestnut (Castanea dentata). (Photo courtesy of Forest and Kim Starr)
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from article Chestnut
Nuts of the Allegheny chinquapin (Castanea pumila). (Photo courtesy of Steve Hurst, USDA–NRCS PLANTS Database)
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from article Genetic mapping
A genetic map shows the relative locations of genes in a linear arrangement. The map is based on the idea of linkage (that is, the closer that two genes are to each other on the chromosome, the greater is the probability that they will be inherited…
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from article Genetic mapping
The process of genetic mapping involves analyses of how traits and genetic markers segregate in experimental or natural populations to determine whether traits and markers (collectively, loci) are inherited together or independently from one…
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from article Genetic mapping
Genetic map of chromosome X showing some of the disorders that are possible. (Copyright © McGraw-Hill Education)
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from article Malvales
Close-up view of a blooming Hibiscus flower. (Photo by Howard F. Schwartz, Colorado State University)
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from article Amphetamine
Molecular structures of amphetamine and methamphetamine (a chemical derivative of amphetamine). (Copyright © McGraw-Hill Education)
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from article RNA World theory
Biochemical functions of the known natural ribozyme classes. Ribozymes are ribonucleic acid (RNA) molecules that can catalyze specific biochemical reactions. The self-cleaving ribozyme classes promote an internal phosphoester transfer reaction to…
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from article RNA World theory
Examples of possibly ancient riboswitches that bind RNA-derived compounds. Riboswitches for the essential cofactor thiamin (thiamine) pyrophosphate (TPP) are present in some species from all domains of modern life, whereas riboswitches for cyclic…
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from article Dallis grass
Dallis grass (Paspalum dilatatum). (Photo courtesy of Larry Allain, USGS National Wetlands Research Center)
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from article Eye (vertebrate)
Diagram of the human eye. (Credit: Shutterstock)
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from article Eye (vertebrate)
Histological section of the vertebrate retina with a light-sensitive area and surrounding tissue. (Credit: Al Telser; copyright © McGraw-Hill Education)
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from article Eye (vertebrate)
Cross section of the vertebrate retina. (Copyright © McGraw-Hill Education)
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from article Eye (vertebrate)
Types of rods and cones found in different vertebrates: (a) goldfish, (b, c) frog, (d) squirrel, (e) human, (f) gecko, (g) goldfish, (h) frog, (i) turtle, (j) human, (k) frog, (l) turtle, (m) snake, and (n) fish. (Copyright © McGraw-Hill Education)
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from article Eye (vertebrate)
The Philippine tarsier (Carlito syrichta) is a nocturnal animal and possesses the largest eyes of any primate. (Credit: William Flaxington)
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from article Eye (vertebrate)
Development of the eye in the human embryo at (a, b, c) 3.5 weeks, (d, e, f) 4 weeks, (g) 4.5 weeks, and (h) 5 weeks. (Credit: Based on an original illustration by Ronan O'Rahilly)
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from article Seasonal affective disorder
Exposure to bright light via a light-therapy box during winter is an effective treatment for individuals suffering from seasonal affective disorder. (Credit: Getty Images)
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from article Seasonal affective disorder
Individuals suffering from seasonal affective disorder often exhibit a variety of symptoms of depression, including increased sleep length, weight gain, and craving for carbohydrates, as well as sexual and social problems, anxiety, lethargy, and…
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from article Plant development
Stages of plant development for a daisy (genus Gerbera) showing the progression from a seedling to a blooming plant. (Credit: Hue Photography/Getty Images)
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from article Plant development
The aboveground body of the plant (shoot) comprises a stack of plant segments termed phytomers. Phytomers consist of a leaflike lateral organ (attached to the stem at a node), a stem (internode), and a lateral meristem or bud. All cells that are…
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from article Plant development
The root (a, b) is built by files of cells and contains three distinct zones of maturation (c). In contrast, the shoot apical meristem (d, e) gives rise to all aboveground plant tissues and comprises zones of cells. The central zone (CZ) maintains…
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from article Plant development
Much of plant morphological diversity can be explained by variations in (a) branching order/pattern, (b) phyllotaxy, and/or (c) leaf shape. (Copyright © McGraw-Hill Education)
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from article Plant development
The ABCE model for floral development. (a) Plants can regulate which type of floral organ is produced in each whorl by restricting the expression pattern of ABCE transcription factors. (b) The four whorls of the flower are shown (stamen, sepal,…
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from article Bromegrass
Smooth bromegrass (Bromus inermis). (Photo by Roselyn Heil, Yellowstone National Park, National Park Service)
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from article Pith
Shoot apex of Coleus blumei, longitudinal section. (After R. A. Popham, Laboratory Manual for Plant Anatomy, C. V. Mosby, 1966)
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from article Pith
Various types of pith in branchlets. (a) Continuous. (b) Diaphragmed. (c) Chambered. (After E. L. Core, Plant Taxonomy, Prentice-Hall, 1955)
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from article Respiratory pigments (invertebrate)
Electron micrograph of hemocyanin molecules from the snail Helix pomatia, showing “pillbox” subunit structure. Circular forms show subunits in a tenfold symmetrical array. There are six parallel rows of subunits in the rectangular forms.
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from article Secretory structures (plant)
Petunia. (a) Young leaf covered with glandular hairs. (b) Higher magnification of the hairs.
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from article Secretory structures (plant)
Hair of stinging nettle.
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from article Secretory structures (plant)
Ceanothus. (a) Longitudinal section of flower. The nectary is ringlike and surrounds the ovary. (b) Enlarged view of a section of the nectary. The epidermis and the small cells beneath it are secretory.
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from article Secretory structures (plant)
Resin duct from pinewood in (a) transverse section and (b) longitudinal section.
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from article Secretory structures (plant)
Laticifers of Nerium oleander. (a) Longitudinal section of shoot tip. The wavy solid lines represent parts of laticiferous cells, which are arranged irregularly. (b) Enlarged view of the area in the rectangle in a showing parts of laticifers with…
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from article Cerebral palsy
The spastic forms of cerebral palsy include diplegia, hemiplegia, and quadriplegia. Diplegia refers to greater involvement of the legs and lesser involvement of the arms, hands, and trunk. Hemiplegia refers to involvement of one side of the body…
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from article Mitosis
Close-up microscopic view (colorized) of a two-cell embryo going through mitosis. (Image courtesy of Andrii Vodolazhskyi, Shutterstock)
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from article Mitosis
Changes in microtubule distribution and chromosome position as an animal cell enters into and proceeds through mitosis. (a) Mid-prophase: chromosomes are condensing within the nucleus. (b) Late prophase/early prometaphase: centrosomes separate; the…
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from article Mitosis
Schematic representation of a mitotic cell, showing the spindle pole (centrosome), spindle microtubule, kinetochore, and chromosome structures.
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from article Mitosis
Representation of the stages of mitosis for a typical animal cell: (a) prophase; (b) prometaphase; (c) metaphase; (d) anaphase; (e) early telophase; (f) late telophase.
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from article Mitosis
Mitotic metaphase. Once all of the chromosomes have acquired a bipolar attachment and have become positioned on the spindle equator, the cell is considered to be in metaphase of mitosis. At this time, the spindle is fully mature and the cell is…
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from article Corn
Corn (Zea mays) growing in a field. (Credit: Bob Nichols, Agricultural Research Service/U.S. Department of Agriculture)
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from article Corn
Ear of field corn on a stalk. The husk has been peeled back to display the kernels (seeds). (Credit: Howard F. Schwartz, Colorado State University)
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from article Corn
The corn leaf at the top is more resistant against leaf blight than the severely damaged leaf on the bottom. (Credit: Keith Weller, Agricultural Research Service/U.S. Department of Agriculture)
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from article Corn
Gall of corn smut, caused by Ustilago maydis, on a stalk of corn. (Credit: H. J. Larsen)
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from article Corn
White ear rot and seedling blight on a corn ear. The pathogen responsible for the afflicted corn is Stenocarpella maydis. (Credit: U.S. Department of Agriculture Cooperative Extension Slide Series/Clemson University)
