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Heart-Rate Monitor

This project uses a sensitive light-detecting resistor to detect small changes in the light beaming through your finger as your blood pumps through tiny arteries in the finger. This device is not the same as the heart-rate monitors typically used in…

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from article Ovary

Ovarian histology. (a) Pika (Ochotona princeps); (b) pocket gopher; (c) prairie dog (Cynomys leucurus); (d) chicken (Gallus domesticus) (from W. Andrew, Textbook of Comparative Histology, Oxford, 1959). (e) Lizard (Xantusia vigilis) (courtesy of M.…

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from article Ovary

Structural formulas of the principal natural estrogens.

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from article Ovary

Active and inactive forms of pregnancy hormone.

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from article Ovary

Hormonal interactions of the hypothalamus, pituitary, and ovary.

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from article Ear (vertebrate)

Generalized diagram of a sensory hair cell found in the ear of all vertebrates.

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from article Ear (vertebrate)

Left-ear external view of the membranous labyrinths of (a) teleost, (b) frog, (c) bird, and (d) mammal. (After A. S. Romer, The Vertebrate Body, 3d ed., Saunders, 1962)

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from article Ear (vertebrate)

Dorsal view of the anterior part of the head and body of an otophysan fish showing the ear and its position relative to the brain. Also shown are the swim bladder and the Weberian ossicles. (From A. N. Popper and S. Coombs, Auditory mechanisms in…

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from article Ear (vertebrate)

Diagrammatic view of the middle and inner ears of a lizard. (After D. Webster and M. Webster, Comparative Vertebrate Morphology, Academic Press, 1974)

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from article Ear (vertebrate)

Schematic drawing of the human ear. (After M. Brödel, Three Unpublished Drawings of the Anatomy of the Human Ear, Saunders)

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from article Ear (vertebrate)

Otic region of the head of a mammal (showing the ear region only). (A. S. Romer, The Vertebrate Body, 3d ed., Saunders, 1962)

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from article Ear (vertebrate)

Inner ear of a mammal. (a) Cross section of a single turn of the cochlea. (b) Organ of Corti. (After D. Webster and M. Webster, Comparitive Vertebrate Morphology, Academic Press, 1974)

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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 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 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 Physiological acoustics

Schematic outline of the central auditory pathways. Numbers indicate the number of neurons from the cochlea. (After S. S. Stevens, ed., Handbook of Experimental Physiology, John Wiley and Sons, 1951)

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from article Physiological acoustics

Distribution of frequency maxima along the basilar membrane. Numbers give frequencies in hertz. Length of basilar membrane = 32 mm, width = 0.04 mm at base, 0.50 mm at apex. (After O. Stuhlmann, An Introduction to Biophysics, John Wiley and Sons,…

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from article Physiological acoustics

Isoamplitude curves of the dc receptor potential within one guinea pig inner hair cell of the basal region. Q10 is a measure of the width of each curve, equal to the center frequency divided by the bandwidth at 10 dB above threshold. (After I. J.…

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from article Physiological acoustics

Intensity/rate functions of two cat cochlear nerve fibers tuned to (a) 2.2 kHz and (b) 10.6 kHz. (After W. D. Keidel and W. D. Neff, eds., Handbook of Sensory Physiology, Springer, 1975)

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from article Physiological acoustics

Tuning curves of a number of nerve fibers in the cat cochlear nerve. (After N. Y.-S. Kiang, Discharge Patterns of Single Fibers in the Cat's Auditory Nerve, MIT Res. Monogr. 35, MIT Press, 1965)

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from article Physiological acoustics

PST histograms for a number of nerve fibers in a cat with various characteristic frequencies, showing response to click stimulation. Each histogram represents 1 minute of data (600 clicks at click rate of 10 per second). (After N.Y.-S. Kiang,…

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from article Physiological acoustics

Response patterns of cells in cat cochlear nuclei, with characteristic frequencies indicated. (a) Primarylike response, 3.5 kHz. (b) Chopper response, 7.0 kHz. (c) Pauser response, 6.6 kHz. (d) “On” pattern, 2.1 kHz. (After R. R. Pfeiffer,…

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from article Physiological acoustics

Ascending (afferent) and descending (efferent) auditory nerve systems. Number labels in the ascending system indicate the number of neurons from the cochlea, while those in the descending system indicate the number of neurons from the auditory…

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from article Excretion

Sequence of breakdown from nucleic acid to ammonia. Reverse pathways broken indicate either lack of knowledge of the mechanism or that other enzymes than those shown are involved. (After M. Florkin, Biochemical Evolution, Academic Press, 1949)

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from article Excretion

Chart of the principle of excretion of a common nitrogenous waste, whether derived from protein or nucleic acid. (After M. Florkin and G. Duchateau, Arch. Int. Physiol., 53:267–307, 1943)

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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 Spermatogenesis

Cellular events in human spermatogenesis. Cell types are labeled.

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from article Microbiology

Two important types of microbes are bacteria (Mycobacterium tuberculosis; left) and fungi (Histoplasma capsulatum; right). [Credit: Janice Haney Carr/Centers for Disease Control and Prevention (left); Libero Ajello/Centers for Disease Control and…

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from article Microbiology

Viruses (Herpes simplex; left) and protozoa (Oxytricha trifallax; right) are microorganisms studied by microbiologists. [Credit: Centers for Disease Control and Prevention (left); National Human Genome Research Institute (right)]

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from article Forensic document analysis

Dots appearing in the background of documents produced by Xerox 5750 digital color copiers and printers.

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from article Forensic document analysis

An illustrative chart showing similar features that appear in both the questioned and specimen handwriting.

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from article Forensic document analysis

The signature on a photocopied contract that was inserted by cutting and pasting a genuine signature from item K5 into position on the contested document. The overlaid ruled graphs confirm that the signatures on items Q1 and K5 are duplicates of one…

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from article Forensic document analysis

The D and LLR values among three examples of the letter “e” written by two writers.

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from article Forensic document analysis

Histograms and parametric probability density functions: (a) same and different histograms for the letter “e” and (b) same and different probability density functions for letter “e.”

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from article Forensic document analysis

Three black ballpoint pen inks analyzed for dating tags using thin layer chromatography. The tag found in ink 1 was added to writing inks manufactured during 1981 and 1991, while no dating tags were detected in inks 2 and 3.

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from article Coenzyme

Nicotinamide adenine dinucleotide (NAD+) is a coenzyme that functions as a hydrogen acceptor for a large number of dehydrogenase enzymes, including alcohol dehydrogenase (ADase). The coenzyme NAD+ needs to be present in order for the oxidation of…

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from article Nervous system (invertebrate)

Electrical potentials and synaptic arrangements. (a) An action potential recorded from the giant axon of the squid. (b) Electrical synapse (two-way). (c) Chemical synapse (one-way).

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from article Nervous system (invertebrate)

Neuron types. (a) Multipolar, isopolar neurons (primitive invertebrate). (b) Unipolar, heteropolar neurons (common invertebrate); arrow indicates direction of information flow. (c) Bipolar neuron (common invertebrate). (d) Multipolar, heteropolar…

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from article Nervous system (invertebrate)

Electrical responses and nervous systems in the lowest invertebrates. (a) Recording from Paramecium illustrates a graded action potential which uses Ca2+ ions in the upswing phase and K+ ions during repolarization; three responses of varying size…

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from article Nervous system (invertebrate)

Nervous systems of the intermediately advanced invertebrates (various worms). (a) Turbellarian flatworm (Notoplana) illustrating nerve cells coming together to form ganglia and nerve tracts (centralization) and nerve cells concentrated in the head…

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from article Nervous system (invertebrate)

Advanced invertebrates as represented by the crustacean nervous system. (a) Crayfish central nervous system (after W. C. Curtis and M. J. Guthrie, Textbook of General Zoology, 3d ed., John Wiley and Sons, 1938). (b) Photomicrograph of cross section…

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from article Nervous system (invertebrate)

Advanced invertebrate nervous system as represented in the marine gastropod mollusk Aplysia. (a) General arrangement of nervous system. (b) Map of the dorsal and ventral surfaces of the abdominal, or parietovisceral, ganglion, indicating the many…

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from article Numerical taxonomy

Similarity matrix showing relationships between clusters of strains of enteric bacteria. (After R. Johnson et al., Numerical taxonomy study of the Enterobacteriaceae, Int. J. System. Bacteriol., 25(1):12–37, 1975)

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from article Numerical taxonomy

Phenogram of 81 species of gulls and terns based on UPGMA cluster analysis of correlation coefficients on 51 skeletal measurements. (After G. O. Schnell, A phenetic study of the suborder Lari (Aves), II. Phenograms, discussions, and conclusions,…

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from article Osmosis

Osmosis process. (Credit: McGraw-Hill Education)

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from article Osmosis

Concept of osmotic pressure. (Credit: McGraw-Hill Education)

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from article Immunology

Various processes are involved in the T cell immune response. T cells are one of the principal cells of the immune system, and they allow a host organism to distinguish between self and nonself and to respond to a target (antigen). Major…

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from article Immunology

Colored scanning electron micrograph (SEM) of B lymphocytes (B cells), which recognize an antigen by means of cell membrane–bound antibodies. (Credit: Steve Gschmeissner/Alamy Stock Photo)

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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 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

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from article Amphetamine

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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 Eye (vertebrate)

Diagram of the human eye. (Credit: Shutterstock)

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from article Eye (vertebrate)

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from article Eye (vertebrate)

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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

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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 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 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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