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from article Learning
Lateral view of the human brain, including the primary areas of the frontal, temporal, parietal, and occipital lobes. (Copyright © McGraw-Hill Education)
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from article Learning
Brain activity can be recorded in various ways, from single-cell activity (top tracing) to the familiar electrical patterns ("brain waves") of an electroencephalogram (bottom tracing). (Credit: Based on an original drawing by C. Cotman and J.…
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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
Typical vertebrate neurons, including the sending neuron and the receiving neuron. (Copyright © McGraw Hill)
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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
Behavior of various Cdk/cyclin complexes and their cellular events. (Copyright © McGraw Hill)
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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
Anatomy of the pituitary gland. (Copyright © McGraw Hill)
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from article Salicylate
Chemical structures of (a) salicylate, the conjugate base of (b) salicylic acid, and the nonsteroidal anti-inflammatory drug (NSAID) (c) acetylsalicylic acid (aspirin).
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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 Gibberellin
Carbon skeleton of ent-gibberellane showing the carbon numbering system and ring designations. (Credit: Peter Hedden)
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from article Gibberellin
The GA-biosynthetic pathway in higher plants via 2-methylerythritol-4-phosphate (MEP). The biologically active end products of the pathway are GA1, GA3, and GA4. The general diterpene precursor trans-geranylgeranyldiphosphate (GGPP) is formed in…
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from article Gibberellin
Mechanisms for GA inactivation. C19-GAs and C20-GAs may be oxidized on C-2 by different classes of GA 2-oxidases (GA2ox). In rice, the enzyme ELONGATED UPPER INTERNODE (EUI) oxidizes the 16,17-double bond of non–13-hydroxylated GAs, such as GA4, to…
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from article Gibberellin
Illustration of a DELLA protein showing conserved domains, and a model for DELLA degradation via the SCF E3 ubiquitin ligase, which consists of a DELLA-specific F-box, Skp1, Cullin1 (CUL), and Rbx1 subunits. Binding of the GID1-GA complex to DELLAs…
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from article Gibberellin
Model for GA-induced production of α-amylase in the aleurone of germinating cereal grains. GAs produced in the scutellum diffuse to the aleurone cells, where they stimulate transcription, processing, and secretion of α-amylase and other hydrolytic…
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from article Spinal cord disorders
Human spinal cord. (Copyright © McGraw-Hill Education)
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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
Four types of chromosomal mutations: (a) deletion, (b) duplication, (c) inversion, and (d) translocation. (Copyright © McGraw-Hill Education)
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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
Formation of duplication and deletion mutations by aberrant recombination. (Copyright © McGraw-Hill Education)
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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
Digital illustration of the human karyotype. The karyotype is the complete set of chromosomes in an organism. (Credit: Science Photo Library/Alamy Stock Photo)
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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. (Copyright ©…
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from article Human genetics
Some common symbols used for the presentation of human pedigrees. (Copyright © McGraw Hill)
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from article Human genetics
Examples of mendelian crosses using two alleles, A and A′. (Copyright © McGraw Hill)
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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. (Copyright © McGraw Hill)
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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
Genetic foundations of development. Genes (the basic units in inheritance consisting of DNA) are conserved throughout evolution and control development. (Copyright © McGraw Hill)
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from article Nerve
Anatomy of a nerve. (Copyright © McGraw Hill)
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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
Overview of the human female reproductive system. (Copyright © McGraw-Hill Education)
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from article Reproductive system disorders
Overview of the human male reproductive system. (Copyright © McGraw-Hill Education)
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from article Reproductive system disorders
The ovaries, fallopian tubes, uterus, cervix, and vagina are sites affected by disorders of the human female reproductive system. (Copyright © McGraw-Hill Education)
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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 Prion
Immunohistochemical staining of cerebellar tissue of a patient who died of variant Creutzfeldt-Jakob disease. Stained amyloid plaques are shown with surrounding deposits of abnormal prion proteins. (Credit: Centers for Disease Control and Prevention)
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from article Prion
Prion replication occurs via a process called seeded polymerization. Differences in PrP amino acid sequences between species (represented by different shades) help to determine whether a prion can cross species barriers by influencing the final…
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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
Hypothetical structure of the archinephros. (Copyright © McGraw-Hill Education)
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from article Urinary system
Mammalian metanephric tubule, showing the renal corpuscle and secretory and collecting portions. (Copyright © McGraw-Hill Education)
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from article Urinary system
Sagittal section of a human metanephric kidney (semidiagrammatic). (Copyright © McGraw-Hill Education)
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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 plastid
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 plastid
Three-dimensional model of grana with intergranal connections. (After W. Wehrmeyer, Planta, 63:13–30, 1964)
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from article Cell plastid
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 plastid
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 plastid
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 Convergent evolution
The streamlining that is prevalent in various unrelated organisms (such as sharks, dolphins, ichthyosaurs, and penguins) is a form of convergent evolution that arose as a result of similar marine lifestyles. (Copyright © McGraw Hill)
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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 Huntington's disease
Huntington's disease is a hereditary disorder that affects approximately five to ten of every 100,000 persons. The average age at onset is between 35 and 40 years. Invariably fatal, the disease progresses gradually over time. (Copyright ©…
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from article Cheese
Cheese being placed in brining tank (salt bath). (Credit: Westend61/Getty Images)
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from article Cheese
Cheese ripening. (Credit: Tom Paiva Photography/Blend Images)
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from article Cheese
Swiss cheese. (Credit: Tom Paiva Photography/Blend Images)
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from article Lignin-degrading fungi
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from article Lignin-degrading fungi
Close-up view of Pleurotus spp. fruiting bodies growing naturally on a dead tree log. The common name of oyster mushroom comes from the shell-like appearance of the fruiting body. Note the characteristic eccentric caps.
