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A common medicine used to relieve mild to moderate pain and reduce fever. Acetaminophen (N-acetyl-p-aminophenol), or paracetamol, is a white crystalline compound with the molecular formula C8H9NO2 (Fig. 1). It is a member of the aniline family of…

A naturally occurring quaternary ammonium cation ester, with the formula CH3(O)COC2H4N(CH3)3+, which plays a prominent role in nervous system function as a neurotransmitter. Acetylcholine (Fig. 1) is an organic compound released from certain…

A disease of the nervous system characterized by a progressive dementia that leads to profound impairment in cognition and behavior. Dementia occurs in a number of brain diseases where the impairment in cognitive abilities represents a decline from…

An ongoing current event in which a large number of living species are threatened with extinction or are going extinct because of environmentally destructive human activities. The Earth is presently in the midst of a mass extinction event. In the…

The cultivation of freshwater and marine species for human purposes. Aquaculture, or aquatic farming, is concerned with the raising of animals and the harvesting of plants in freshwater and marine environments (Fig. 1). In other words, it is the…

The scientific discipline that studies the origin, evolution, distribution, and future of life in the universe. Astrobiology is an interdisciplinary science integrating contributions from biology, geology, astronomy, paleontology, and planetary…

A neurodevelopmental condition that impairs the way that a person relates to and communicates with other people. Persons with autism have difficulties with social communication and interaction. They also can have unusual behaviors, such as…

The part of the nervous system that controls visceral (internal organ) functions of the body. The autonomic nervous system is a component of the peripheral nervous system, or PNS, which, along with the central nervous system, or CNS, represents the…

The ongoing lower level of species extinction intensity occurring between episodes of mass extinctions. Extinction is a normal part of the history of life. Out of every 100 species that have ever lived on Earth, 99 are no longer in existence.…

The function and transport of the bicarbonate ion for maintaining the acid level (pH) throughout the body for stable physiological processes; disfunction of bicarbonate transport results in disease. Bicarbonate (HCO3−) is a small inorganic negative…

Any of the self-sustained circadian (approximately 24-hour) rhythms that regulate daily activities, including sleep and wakefulness. A biological clock is any physiologic factor that functions in regulating innate organismal rhythms. Biological…

Any of the cells within a tumor that possess the capacity to self-renew and cause the heterogeneous lineages of cancerous cells that comprise the tumor. Cancer stem cells (CSCs) typically represent a small percentage of all cells in a tumor (rarely…

The portion of the nervous system composed of the brain and spinal cord in vertebrates. The division of the vertebrate nervous system comprising the brain and spinal cord is known as the central nervous system (see illustration). In general, the…

A DNA and protein complex that is found in the nuclei of eukaryotic cells and stores most of the genetic information for a species. Chromatin was first discovered and named by German biologist Walther Flemming in 1879. While staining cells to…

The internal structures and processes that are involved in the acquisition and use of knowledge, including sensation, perception, attention, learning, memory, language, thinking, and reasoning. The mental processes and behaviors that constitute…

A psychotherapy with roots in both cognitive science and behavioral science. Cognitive-behavioral therapy (CBT) is the most widely used evidence-based psychotherapeutic practice for a variety of mental health disorders, including anxiety, depression…

The response of corals to environmental stress in which they eject the single-cell algae that live within the transparent coral tissue, making the white coral skeleton visible. Corals (Fig. 1) are animals that live in a partnership (symbiosis) with…

Any peripheral nerve that has its central nervous system connection with the brain, as opposed to the spinal cord, and reaches the brain through a hole (foramen) in the skull. The cranial nerves are involved in providing sensory and motor…

A genome-engineering technique that allows precise targeting of specific stretches of genetic code and editing of DNA at designated locations. The CRISPR/Cas9 system has been used as a general tool to engineer the genomes of many different…

A syndrome characterized by a generalized decline in cognition that is severe enough to cause functional impairment in daily activities. Dementia is a term used to describe a collection of symptoms of severe cognitive decline. Individuals suffering…

The interaction of the behavior and ecology of hosts with the biology of pathogens as relating to the impact of diseases on populations. Although human diseases have been studied from an ecological perspective for centuries, diseases in plant and…

A term commonly associated with both behaviors and states of mind (known as feelings) that are not under the control of reason and disturb the flow of consciously directed behavior. Emotions influence human thinking and behavior (Fig. 1), and they…

An international consortium of research groups dedicated to determining how the human genome functions.Many human diseases are caused by changes in the abundance or activity of proteins, and proteins are encoded by segments of DNA called genes (Fig.…

The study of heritable (stable) changes in gene expression and function that are not attributed to alterations of the DNA sequence. The epigenome represents the complete set of epigenetic modifications possessed by an organism or an individual cell.…

A condition characterized by the paroxysmal recurrence of transient, uncontrollable episodes of abnormal neurological or mental function (or both). "Epilepsy" generally refers to the medical condition of recurrent, unprovoked seizures, and the term…

An interdisciplinary science area that is concerned with modeling aspects of natural evolution in order to solve real-world problems of optimization. Living organisms, as well as those that are long extinct, demonstrate optimized complex behavior at…

A sense organ that acts as a photoreceptor capable of image formation. The eye of vertebrates is a specialized light-sensitive sensory structure that provides these animals with vision (the sense of sight). It is constructed along a basic anatomical…

The upper part of the female oviduct present in humans and other higher vertebrates, also known as uterine tube. The fallopian tube extends from the ovary to the uterus and transports ova from the ovary to the cavity of the uterus. Each tube is…

A coenzyme primarily used by many enzymes of the oxidoreductase enzyme class. Flavin adenine dinucleotide (FAD) is employed either as a freely diffusible molecule or as a covalently bound prosthetic group within flavoproteins, which are proteins…

The use of pollen and spore evidence in legal cases. In its broader application, the field of forensic palynology also includes legal information derived from the analysis of a broad range of microscopic organisms that can be found in both fresh and…

The intentional production of new genes and alteration of genomes by the deletion, substitution, or addition of new genetic material. Genetic engineering involves the artificial recombination of nucleic acid molecules in the test tube; their…

A plant that has altered genetic material (DNA) through recombinant DNA (rDNA) manipulation. Genetic engineering of plants allows for very specific genetic changes to be made to a plant's deoxyribonucleic acid (DNA), as opposed to the random…

A commercially grown plant that has altered genetic material through artificial recombinant manipulation. Genetic modification is the latest scientific tool for developing improved crop varieties. Such genetically modified (GM) crops can help to…

A biological organism whose genetic material has been manipulated artificially through genetic or genomic editing techniques. In contrast to the long history of artificial selection (domestication), in which humans selectively breed organisms to…

Resident non-neuronal cells that actively influence the development and function of the nervous system. Glial cells, also referred to as glia and neuroglia, are found in both the central nervous system (CNS) and the peripheral nervous system (PNS).…

One class of several hormones that are produced in the outer part of adrenal glands, known as the cortex. Glucocorticoids (GCs) are crucial for regulating metabolism, the immune system, blood pressure, and other essential functions (see…

A simple sugar, or monosaccharide, with the chemical formula C6H12O6; also called dextrose, d-glucopyranose, cerelose, grape sugar, and corn sugar. Glucose is a monosaccharide carbohydrate with six carbon atoms. It is the most common sugar and the…

A space-traversing unmanned vehicle which contains the means for controlling its flight path and that delivers an explosive warhead with high accuracy. Various kinds of missiles are guided in the sense that they can aerodynamically adjust after…

The region of the body consisting of the skull, its contents, and related structures. Its two principal parts are the cranium, or braincase, and the face.The skin, hair, and subcutaneous tissues over the top of the skull are collectively known as…

Pathologies or aberrations in structure or function of blood cells or the blood-clotting mechanism. Hematologic disorders affect the blood and blood-forming organs. Although many diseases and abnormal conditions may be reflected by the blood and its…

The process by which the cellular elements of the blood are formed. Blood contains many free-floating cells that are moved throughout the body within the blood vessels. The three main types of blood cells are the red cells (erythrocytes), which…

The iron-containing, oxygen-carrying protein molecule of red blood cells. The protein hemoglobin (Fig. 1), which carries oxygen and contains iron, represents more than 95% of the solid constituents of the red blood cell. It is found in almost all…

Any of the chemical messengers produced chiefly by endocrine glands, whose secretions are liberated directly into the bloodstream and transported to a distant part or parts of the body, where they exert a specific effect for the benefit of the body…

A mature cell that has been reprogrammed genetically to an embryonic-like state that then can give rise to one of many different cell types. Induced pluripotent stem cells (iPS cells; Fig. 1) represent a major breakthrough in stem cell research.…

The entrance, growth, and multiplication of a microorganism or pathogen in the body of a host. Infection may or may not result in the establishment of a disease process, depending on many variables including the pathogen involved, the health of the…

A species translocated from one region or continent to another outside its normal range, particularly when the translocation is the result of human activity (intentional or otherwise). Many thousands of species, including animals, plants, fungi,…

A protein that spans cellular membranes and mediates the passage of electrolytes across the hydrophobic barrier that maintains the integrity of the cell and interior compartments. Ion channels are found in both prokaryotes and eukaryotes and their…

A salt or ester of lactic acid (CH3CHOHCOOH). In lactates, the acidic hydrogen of the carboxyl group has been replaced by a metal or an organic radical. Lactates are optically active, with a chiral center at carbon 2. The two optical isomers of a…

The physiologic and metabolic processes involved in the assimilation of dietary lipids and in the synthesis and degradation of lipids. Lipids (Fig. 1) form a class of compounds composed of neutral fats (triglycerides), phospholipids, glycolipids,…

The mental ability to store and access information that has been acquired through experience. Memory (Fig. 1) is a critical component of practically all aspects of human thinking, including perception, learning, language, and problem solving.…

A device that is capable of converting chemical energy into electrical energy with the use of whole bacterial cells as the catalyst. Fuels that are produced biologically are known as biofuels. Biofuel cells convert chemical energy from organic…

A portion of the nervous system that regulates and controls the contractile activity of muscles and the secretory activity of glands. The motor systems of the body are highly complex networks responsible for muscular movements and gland secretions.…

An autoimmune disease resulting from an abnormality in neuromuscular transmission, characterized by a fluctuating degree of muscle weakness. Myasthenia gravis is a chronic autoimmune neuromuscular disorder (see illustration) characterized by varying…

The functional unit of a kidney, consisting of a glomerulus with its capsule and a renal tubule. The kidney is an organ responsible for filtering the blood and creating urine. Blood enters the kidney via the renal artery and makes its way through a…

A nerve cell; the functional unit of the nervous system. A neuron is a specialized, basic nerve cell that transmits and receives information, in the form of electrical impulses, throughout the body. With the exceptions of sponges and placozoa, the…

A progressive degenerative disorder of the nervous system belonging to a group of conditions called motor system disorders. Parkinson's disease—more specifically known as idiopathic Parkinson's disease to distinguish it from the four Parkinson-plus…

A regulator of cellular lipid storage and the major surface coat protein of cytoplasmic lipid droplets. Perilipins (derived from the Greek words for “surrounding lipid”) are primary regulators of cellular lipid storage. The perilipins sequester…

One of a class of cyclic compounds in which the parent macrocycle consists of four pyrrole-type units linked together by single carbon bridges. Several porphyrins with selected peripheral substitution and metal coordination carry out vital…

Any of the small particles, present in large numbers in every living cell, whose function is to convert stored genetic information into protein molecules. Ribosomes are cellular factories that make proteins and are essential for life in organisms…

A neurological condition in which there are recurrent seizures. Seizure disorders result from periodic disturbances to the electrical (nerve cell) activity of the brain, leading to temporary and uncontrolled brain dysfunction. Seizure conditions are…

The genetic mechanisms by which sex is determined in all living organisms. The mechanisms of sex determination allow individual organisms to develop characteristics that are indicative of a certain sex (male, female, or hermaphrodite) [Fig. 1].…

A family of nicotinamide adenine dinucleotide (NAD)–dependent protein deacetylases (enzymes that remove acetyl groups from protein molecules) and adenosine diphosphate (ADP)–ribosyltransferases (enzymes that catalyze the transfer of the ADP-ribose…

A general term for the somatic sensibilities aroused by stimulation of bodily tissues such as the skin, muscles, tendons, joints, and the viscera. Six primary qualities of somatic sensation are commonly recognized: touch-pressure (including temporal…

The portion of the central nervous system within the spinal canal of the vertebral column. In vertebrates, the central nervous system is composed of the brain and spinal cord (Fig. 1). The spinal cord extends from the foramen magnum at the base of…

Any of the cells that have the ability to self-replicate and to give rise to mature cells. The concept of stem cells (Fig. 1) was originally based on renewing tissues. Many adult tissues, including the skin, blood, and intestines, consist of mostly…

The physiologic mechanism by which one nerve cell (neuron) influences the activity of an anatomically adjacent neuron with which it is functionally coupled. Synaptic transmission (Fig. 1) enables a neuron to communicate with a target cell across a…

A rare genetic disorder in which there is a deficiency of hexosaminidase A (a lysosomal enzyme that hydrolyzes GM2 gangliosides). Tay-Sachs disease is a severe and progressive neurodegenerative disease. Because of the deficiency of hexosaminidase A…

An aqueous solution of organic and inorganic substances—mostly waste products of metabolism—that collects in the kidneys and is removed from the body primarily through the urinary bladder and urinary tract. Urine is a liquid waste produced by the…

A sensory system that provides the information required for proper sense of balance and spatial orientation. The vestibular system detects motion of the head in space and, in turn, generates reflexes that are crucial for daily activities, such as…

Diseases that are transmitted from animals to humans. Zoonoses (the singular form is zoonosis) are also termed zoonotic diseases. They are infectious diseases passed from animals (Fig. 1) to humans. Zoonotic agents are found among all major…

A major plant hormone that plays an important role in plant growth and development. Abscisic acid (ABA), with a chemical formula of C15H20O4 (Fig. 1), is one of the most significant hormones found in plants. It is responsible for regulating various…

A viral disease of humans caused by the human immunodeficiency virus (HIV), which attacks and compromises the body's immune system. Individuals infected with the human immunodeficiency virus (HIV) proceed through a spectrum of stages that ultimately…

Habituation to a specific practice, such as drinking alcoholic beverages or using drugs (for example, heroin, cocaine, or amphetamines), and disorders characterized by the chronic use of a drug, alcohol, or similar substance. Addiction and addictive…

A complex endocrine organ in proximity to the kidney. The adrenal gland (see illustration), often called simply as the adrenal, is an important endocrine organ located on top of the kidneys. Adrenal gland tissue is present in all vertebrates from…

Any disorder of recognition. Agnosia is a rare neurological condition in which an individual fails to recognize and identify persons or objects (see illustration). Typically, agnosia is the result of damage to specific areas of the brain.…

Mechanized systems of food and fiber production used in agriculture. The mechanized systems comprising agricultural machinery are utilized in numerous aspects of agriculture, including the initial tillage of the soil (Fig. 1), planting, cultural…

A plasma protein produced by the liver that maintains fluid balance in the blood and transports fatty acids in the plasma and interstitial fluid. Albumin is the most abundant protein in human serum (see illustration), as well as being one of the…

The repeated and/or excessive use of alcohol (ethanol) that continues despite negative physical, psychiatric, or social consequences. Alcoholism is characterized by consuming alcohol more often, in larger amounts, or over longer periods than…

Any of a number of alternative forms of a gene. An allele is a variant form of a gene (see illustration). Allele is a contraction of allelomorph, which is a term that William Bateson used to designate one of the alternative forms of a unit showing…

A small, tropical, evergreen tree (Pimenta dioica) and its dried, unripe fruit (berry). Allspice (Pimenta dioica; alternatively, P. officinalis) [see illustration] is a member of the myrtle family (Myrtaceae). Allspice, which is also known as…

A glycoprotein that is normally present in significant amounts only in the serum of the fetus. Alpha fetoprotein (AFP) is an important plasma glycoprotein found in a developing fetus. This protein is also detectable in the mother's blood by passing…

Any of the plant growth forms characteristic of the upper reaches of mountain slopes. Alpine vegetation refers to the plants that grow in mountainous areas above the limit of subalpine trees and other subalpine vegetation. In such environments,…

An intergrading region on a mountain slope characterized by specific plant life forms or species composition, and determined by complex environmental gradients. Along an altitudinal transect of a mountain, there are sequential changes in the…

Any of the organic compounds possessing one or more basic amino groups and one or more acidic carboxyl groups. Of the more than 80 amino acids that have been found in living organisms, approximately 20 serve as the building blocks for proteins.…

A significant, yet relatively selective loss of memory. Amnesia is a type of memory loss, often resulting from brain disease or injury (see illustration). The inability to remember can be temporary or permanent. In general, amnesia can be…

A generalized or localized tissue reaction occurring within minutes of an antigen-antibody reaction. Anaphylaxis is a severe allergic reaction and immune response that can be life-threatening. Similar reactions elicited by nonimmunologic mechanisms…

A class of steroid hormones produced in the testes and adrenal cortex that act to regulate masculine secondary sexual characteristics. The major naturally occurring androgens, such as testosterone, are C-19 steroids (that is, they each contain 19…

A synthetic manufactured drug derived from the male sex hormone testosterone. Androgenic-anabolic steroids, often termed simply as anabolic steroids, are artificially produced testosterone variants. They can provide a number of medical benefits when…

The increase in size or weight of an animal. Animal growth is an increase in an animal’s size or mass over its lifetime. Growth, which is often associated with progressive development, may extend throughout the animal's life or it may be limited to…

The formation of new animal individuals, which may occur by asexual or sexual means. All animals must reproduce asexually or sexually to create new individuals of their species. In asexual reproduction, a single parent can produce offspring that are…

The use of live nonhuman animals for scientific research and experimentation. Animal testing has been a cornerstone of biomedical research, having contributed greatly to the understanding of human biology, to the unraveling of the complex underlying…

A disorder of language acquired as a result of brain disease. Aphasia is impairment in the use of spoken or written language caused by brain disorders (see illustration) that cannot be explained by paralysis or incoordination of the articulatory…

The application of ecological principles to the solution of human problems and the maintenance of a high quality of life. Applied ecology is a branch of ecology that applies concepts of ecology to address contemporary problems involving natural…

An impairment in the performance of voluntary actions despite intact motor power and coordination, sensation and perception, and comprehension. Apraxia is a neurological condition in which there is difficulty with skilled tasks or learned movements…

Any vegetable that is prevalent in Asian cuisines, but less well known in Western diets. Asian vegetables (Fig. 1), also referred to as Asian greens or oriental vegetables, are very important in Asian countries, but are not as popular in North…

Any treatment or procedure that includes the in-vitro handling of oocytes (immature ova or egg cells) and sperm or embryos for the purpose of establishing a pregnancy. Assisted reproductive technology (ART) is undertaken as a treatment of…

A common psychiatric disorder (especially in children) characterized by attentional difficulties, impulsivity, and hyperactivity. Attention deficit hyperactivity disorder (ADHD) is a mental disorder marked by an individual's inability to pay…

Any of a class of plant growth substances (phytohormones or plant hormones) that have an essential role in coordination of many growth and developmental processes during the life cycle of plants, especially the ability to increase the rate of shoot…

A highly contagious intestinal disease, also known as shigellosis, caused by rod-shaped bacteria of the genus Shigella. Bacillary dysentery, which also is referred to as shigellosis, is a significant intestinal infection. Rod-shaped bacteria of the…

The production of visible light (usually blue-green) by bacteria. Luminous bacteria emit visible light by converting chemical energy to light energy. The phenomenon of bacterial luminescence is seen in many species of several genera, including…