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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 Biofilm

Biofilms are highly structured communities of microorganisms that are surface-associated or attached to one another, and are enclosed within a self-produced protective extracellular matrix. Biofilm formation and actions involve a number of stages:…

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from article Lung

Human lungs: (a) The trachea bifurcates as the right and left primary bronchi that enter each lung. The bronchi subdivide further to form the bronchial tree. (b) Color-coded view of the major branches of the bronchial tree. (Copyright © McGraw-Hill…

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from article Animal testing

Mice are the most commonly used vertebrate species in animal testing and research. (Credit: Dolores Bonaparte)

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from article Animal testing

The use of animals in biomedical research remains essential, but the handling of these sentient beings must be done humanely to minimize and prevent animal harm. (Credit: U.S. Department of Agriculture)

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from article Circadian clock (plants)

Three-module circadian clock system.

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from article Circadian clock (plants)

Model of the Arabidopsis circadian clock, showing light input (bold arrow), the central oscillator (large box) and output/response (tinted arrows). Light signals synchronize the clock via the cryptochromes (cry) and phytochromes (phy). These are…

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from article Anthrax

A color-enhanced scanning electron micrograph 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 of…

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from article Anthrax

Micrograph (stained with hematoxylin and eosin) showing submucosal hemorrhage in the small intestine of a person fatally affected by gastrointestinal anthrax. (Credit: Marshal Fox/Centers for Disease Control and Prevention)

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from article Neuron

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from article Mutagens and carcinogens

Arsenic is a known carcinogen. In this graphical example, more than half of the mice exposed to arsenic in their drinking water [at concentration levels of 50 and 500 parts per billion (ppb)] showed increased incidences of lung tumors (compared to a…

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from article Mutagens and carcinogens

Proflavin is a chemical disinfectant agent against bacteria, causing mutagenic DNA changes (such as the insertion or deletion of a DNA base pair). However, it is carcinogenic in mammals. Thus, it is used only for the disinfecting of surfaces or for…

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from article Mutagens and carcinogens

Model of carcinogenesis. Changes often occur in the growth properties of normal cells, leading to cancer cells that are not responsive to normal regulatory controls and can eventually give rise to a visible neoplasm or tumor. The main stages of the…

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from article Autophagy

Modes of autophagy in yeast and mammalian cells. Macroautophagy involves the uptake of cytoplasm at a site away from the lysosome or vacuole. The origin of the sequestering membrane is not known, but it likely includes multiple sources such as the…

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from article Autophagy

Basic steps involved in macroautophagy, shown with the structural intermediates. See the text for full details.

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from article Autophagy

The cytoplasm-to-vacuole targeting (Cvt) pathway is an example of selective autophagy. The schematic illustrates the steps of the Cvt pathway and also shows electron micrographs of the sequestration event. Precursor aminopeptidase I (prApe1) forms a…

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from article Autophagy

Atg8 tagged with white fluorescent protein (GFP-Atg8) can be used to monitor autophagosome formation. Cells in growing conditions (for example, in the presence of nitrogen; +N) carry out a basal level of macroautophagy and typically display a single…

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from article Cell cycle

Phases of the eukaryotic cell cycle. Interphase is subdivided into three phases: gap phase 1 (G1), synthesis (S), and gap phase 2 (G2). M phase, which follows interphase, consists of mitosis (nuclear division) and cytokinesis (cell division). G0…

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from article Cell cycle

During cytokinesis (cell division), the cell pinches into two parts between the separated daughter nuclei. At the end of this process, the two daughter cells often remain tethered by a thin "midbody" of microtubules. Once this midbody breaks, the…

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from article Cell cycle

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from article Pituitary gland

The pituitary, also known as the hypophysis, is a pea-sized gland situated at the base of the brain. The hypothalamus is designed and anatomically positioned to receive a diversity of messages from external and internal sources that can be…

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from article Pituitary gland

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from article Meningococcus

A photomicrograph reveals the presence of the bacterium Neisseria meningitidis, which can be pathogenic, leading to meningococcal meningitis. (Credit: James Volk/Centers for Disease Control and Prevention)

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from article Oxygen toxicity

The dual effect of oxygen on biologic activity. Organisms that avail themselves of the enormous metabolic advantages provided by dioxygen (O2) must defend themselves against its toxicity. (Copyright © McGraw Hill)

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from article Spinal cord disorders

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from article Thirst and sodium appetite

Regulation of cellular water. ADH = antidiuretic hormone.

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from article Thirst and sodium appetite

Hypovolemic thirst and sodium appetite are caused by altered sensory information from an underfilled circulation, reinforced by increases in circulating angiotensin II and mineralocorticoids. Angiotensin peptides generated from components of a…

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from article Mutation

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from article Mutation

The karyotype (complement of chromosomes) characteristic of an individual with Down syndrome. Note that there are three copies of chromosome 21; this mutation is known as trisomy 21. (Copyright © McGraw-Hill Education)

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from article Mutation

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from article Antibody

Computer-generated models of (a) an antibody molecule and (b) a metalloantibody molecule. The amino acid side chains have been omitted for clarity. In panel (a), blue indicates the constant regions of light chains and heavy chains; white, the…

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from article Antibody

Typical antibody molecule. There are two H and two L chains, held together by disulfide bonds, and the N-terminal variable domains are shown in dark color. The molecule is bilaterally symmetrical, so two identical epitopes are bound. The…

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from article Antibody

Domain structure of three typical light (L) and heavy (H) chains shows their similarities and differences. The amino- and carboxy-terminals of the chains are marked N and C, respectively. The flexible hinge region is also shown. At the N-terminals,…

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from article Bioassay

In conducting bioassays, researchers often employ laboratory culture tests, which use, for example, bacteria cultured in a petri dish (usually to model an effect on the organism of interest or on some basic cellular function). (Credit:…

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from article Amniota

Basic types of vertebrate eggs.

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from article Amniota

Embryo developing in amniote eggs.

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from article Human genetics

A genetic map is a type of chromosome map that shows the relative locations of genes and other important features. 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…

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from article Human genetics

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from article Human genetics

The double-helix structure of a DNA molecule. (Credit: Darryl Leja/National Human Genome Research Institute)

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from article Human genetics

Simplified diagram showing (a) the structure of a gene, (b) the mature messenger RNA (mRNA) after the two intervening sequences have been spliced out and the “cap” and “tail” added, and (c) the polypeptide translated from the mRNA.

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from article Human genetics

Some common symbols used for the presentation of human pedigrees.

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from article Human genetics

Examples of mendelian crosses using two alleles, A and A′.

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from article Human genetics

Typical pedigree pattern of a rare autosomal-dominant trait: classical achondroplastic dwarfism. Individuals with this anomaly, caused by a defect in bone growth, have extremely short arms and legs, but are otherwise normal. I–IV are generations;…

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from article Human genetics

Typical pedigree pattern of a rare autosomal-recessive trait: albinism.

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from article Human genetics

Typical pedigree patterns of a sex-linked recessive trait: hemophilia A. (a) Only males are affected and usually come from unaffected mothers, who often have affected fathers or brothers. (b) An affected female can result from an affected father and…

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from article Developmental genetics

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from article Microbiome

Profile of the human microbiome by anatomical niche. DNA sequence analysis reveals the relative abundances of the six most abundant bacterial phyla in the human body. The phyla shown represent 99.6% of the sequences sampled. Cyanobacteria were…

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from article Microbiome

Cup-and-ball diagrams to conceptualize the ecosystem equilibrium of the microbiota. (a) A diverse microbial ecosystem requires a large amount of applied force (blue arrow; for example, an antibiotic disturbance) to push it out of its stable…

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from article Acquired immune deficiency syndrome (AIDS)

HIV targets helper T lymphocytes. This illustration shows HIV cells attaching to CD4 coreceptors on a helper T lymphocyte. The depletion of these helper T lymphocytes leads to acquired immune deficiency syndrome (AIDS). (Copyright © McGraw-Hill…

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from article Acquired immune deficiency syndrome (AIDS)

Scanning electron micrograph of HIV-1 virions budding from a cultured lymphocyte. Multiple round bumps on the cell surface represent sites of assembly and budding of virions (green spheres). (Credit: C. Goldsmith/Centers for Disease Control and…

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from article Cell motility

Electron micrograph (colorized) of microtubules purified from calf brain cytoplasm. Rows of tubulin subunits along the microtubule axis can be discerned by close inspection. In general, microtubules comprise one of the two basic molecular systems…

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from article Reproductive system disorders

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from article Reproductive system disorders

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from article Reproductive system disorders

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from article Reproductive system disorders

The testicles (testes), epididymis, vas deferens and seminal vesicles, prostate gland, urethra, and penis are sites affected by disorders of the human male reproductive system. (Copyright © McGraw-Hill Education)

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from article Speech

Human head and thorax. (Courtesy of G. E. Peterson)

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from article Speech

Action of the glottis during speech. (a) Six successive positions of the vocal folds in one vibration cycle at 120 Hz. (b) Relation between pitch and vocal fold tension. (Courtesy of D. W. Farnsworth)

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from article Speech

Sound spectrograms of the utterance “speech production.” (a) Energy patterns: A, pulse; B, periodic; C, aperiodic; and D, silence. (b) The dotted lines represent the pitch pattern of the utterance.

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from article Speech

Computer-generated three-dimensional spectral display of the spoken syllable “yah.”

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from article Speech

Speech flakes of vowels in the words (a) “far,” (b) “food,” and (c) “fee.” (Courtesy of Charles Wooters)

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from article Speech

Regions of the brain involved in speech. (a) Left hemisphere, usually more involved in speech functions than the right hemisphere. (b) A model for the neural processes involved in speaking a heard word. Arrows indicate the path of the relayed signal…

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from article Immunological ontogeny

Schematic representation of the differentiation of the immune system.

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from article Hygiene hypothesis

The hygiene hypothesis suggests that young children should be exposed to various environmental microorganisms, including those found in soils, so that proper development of the immune system can take place. (Credit: Allison Peltzman/Shutterstock)

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from article Hygiene hypothesis

Scanning electron micrograph of a human T cell (T lymphocyte) from the immune system of a healthy donor. (Credit: National Institute of Allergy and Infectious Diseases, National Institutes of Health)

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from article Antimicrobial agents

A researcher examining a disk diffusion antimicrobial susceptibility plate. Antibiotic action can be assessed by measuring the zones of inhibition surrounding antibiotic-impregnated filter paper disks. (Copyright © McGraw-Hill Education)

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from article Urinary system

The urinary system, which consists of the kidneys, urinary ducts (ureters and urethra), and bladder, functions in the elaboration and excretion of urine in vertebrates. (Copyright © McGraw-Hill Education)

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from article Urinary system

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from article Urinary system

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from article Urinary system

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from article Urinary system

The tubular countercurrent mechanism for concentrating the urine, and the exchange system in the straight hairpin blood vessels of the medulla, which minimizes loss of solute from medullary interstitial fluid. Arrows indicate the direction of…

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from article Social mammals

Meerkats (Suricata suricatta) are notable social mammals. Here, they are looking for danger outside of their den. (Credit: Alta Oosthuizen/Shutterstock)

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from article Social mammals

An adult female African lion (Panthera leo) nurses four cubs. The early ingestive behavior (nursing) of mammals has a high degree of social significance. (Credit: Glow Images)

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from article Social mammals

Mexican spider monkeys (Ateles geoffroyi vellerosus) are primates that display many examples of social behavior and organization. (Credit: Oksana Kunka/123RF)

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from article Escherichia coli outbreaks

A digitally colorized electron micrographic image of an E. coli O157:H7 bacterium, which is a common cause of foodborne disease outbreaks. The flagella of this bacterium can be seen in the image. (Credit: Elizabeth H. White/Centers for Disease…

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from article Escherichia coli outbreaks

A digitally colorized scanning electron micrographic image of a growing cluster of rod-shaped E. coli O157:H7 bacteria. The O157:H7 strain makes a powerful toxin called Shiga toxin, which causes diarrheal disease and other gastrointestinal ailments…

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from article Cell plastids

Light microscope view of part of Hypochaeris radicata leaf, showing chloroplasts sectioned in a variety of planes and displaying internal grana.

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from article Cell plastids

Three-dimensional model of grana with intergranal connections. (After W. Wehrmeyer, Planta, 63:13–30, 1964)

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from article Cell plastids

Electron microscope view of two oat leaf chloroplasts, one showing successive layers of grana in side view, and the other showing grana in face view (disk shape of constituent thylakoid lobes are seen).

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from article Cell plastids

Part of oat leaf chloroplast at higher magnification. Grana are seen in side view, revealing profiles of membranes. Thylakoids that interconnect grana are shown, with components of stroma, or ground substance, in which thylakoids lie. The dense…

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from article Cell plastids

Proplastid in cell of broad bean root tip. Double membranous envelope is shown and rudimentary nature of internal membrane system is obvious.

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from article X-ray microscope

Principles for x-ray microscopy. (a) Contact microradiography. (b) Projection x-ray microscopy. (c) Reflection x-ray microscopy. (d) X-ray image spectrography.

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from article Vibrotaction

Block diagram of apparatus for determining vibrotactile perception thresholds at the fingertip.

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from article Vibrotaction

Tactogram showing the approximate maximum threshold recorded at the fingertips of healthy persons (horizontal line), and examples of two types of threshold elevation (reduction in acuity) at selected frequencies (circles and squares).

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from article Forensic botany

Surface of a green bean pod, showing its spines using (a) light microscope (courtesy of David O. Norris) and (b) scanning electron microscope (courtesy of Meredith Lane).

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from article Anthropology

Fossil skulls of four different species of Homo (clockwise from upper left): Homo neanderthalensis, Homo antecessor, Homo erectus, and Homo sapiens. Each skull shows different anatomical variations. (Credit: creativemarc/Shutterstock)

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from article Anthropology

The indigenous inhabitants of Siberut Island (West Sumatra, Indonesia) are known as the Mentawai people. They live a seminomadic hunter-gatherer life in the coastal and rainforest environments of the island. (Credit: Chanwit Whanset/Shutterstock)

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from article Dentition

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from article Pain

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from article Atomic force microscopy

Principle of AFM.

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from article Atomic force microscopy

Application of AFM imaging to lipid membranes. (a) Nanostructures with well-defined bendings and a ∼30 nm periodicity, formed at the surface of a mixed dipalmitoylphosphatidylcholine/surfactin bilayer supported on mica. (b) Another type of…

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from article Atomic force microscopy

Application of AFM force spectroscopy to the detection of single molecular recognition events. Force–distance curves were recorded between an AFM tip and a substrate functionalized with oligoglucose and concanavalin A, respectively. The ∼100 pN…

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from article Signal transduction

Different receptors and their mechanism of action: G-protein–coupled receptor (GPCR), receptor tyrosine kinase (RTK), adenylyl cyclase (AC).

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from article Signal transduction

Steps in the activation of the MAPK pathway leading to cell proliferation.

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from article Signal transduction

Steps in the glucagon-stimulated release of glucose stores from cells.

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from article Nitrogen-fixing trees

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from article Nitrogen-fixing trees

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from article Lipoprotein

Structural model of a lipoprotein.

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from article Anthropocene extinction

The relationship between species extinctions and the human population on Earth since the year 1800. As the human population has increased, so too have the numbers of species extinctions. The numbers have been so great that the current Anthropocene…

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from article Vitamin K

Vitamin K. (a) Natural forms. (b) Regeneration of the hydroquinone for γ-carboxyglutamate (Gla) synthesis; Glu = glutamic acid. Vitamin K functions by carboxylating certain glutamate residues in a few proteins. With each carboxylation reaction, a…

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from article Vertebrata

The subphylum Vertebrata constitutes the largest natural group (clade or monophyletic group) of chordate animals (members of the phylum Chordata). The asterisk indicates that birds are included in the reptile group. (Copyright © McGraw Hill)

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