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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 conductor whose purpose is to emit and/or receive electromagnetic waves using the bulk oscillations of electric charges within the conductor. The conduction electrons in antennas are free to move throughout the conductor. The electrons form a bulk…

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 subfield of computer science concerned with understanding the nature of intelligence and constructing computer systems capable of intelligent behavior. Many activities, such as perception, learning, planning, natural language, and understanding,…

Earth's oldest desert and the most arid place outside of Antarctica's Dry Valleys. Located along the edge of the Pacific Ocean and to the west of the Andes in Chile's Antofagasta Province, the Atacama Desert (Fig. 1) has long been recognized as…

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 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 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…

Cameras in mobile phones or smartphones that can capture images and videos.The cellphone, the world’s favorite must-have gadget, has been with us for nearly a half-century, while experiencing continuous and often phenomenal improvements. Much of the…

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 branch of computer science that deals with the theory and techniques of computer-generated images. Computers produce images by analyzing a collection of dots, or pixels (picture elements). Computer graphics is used to enhance the transfer and…

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…

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 radar system used to measure the relative velocity of targets and their position. The operation of these systems is based on the fact that the Doppler frequency shift in the target echo is proportional to the radial component of target velocity.…

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.…

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…

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…

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…

An ordered, internally consistent, internationally recognized sequence of time intervals, each distinct in its own history and record of life on Earth, including the assignment of absolute time in years to each geologic interval. The geologic time…

Significant and persistent changes in the state of Earth’s climate. Earth's past climates, or paleoclimates, have alternated between ice ages and periods warmer than today over relatively long time scales (millions to tens of millions of years)…

The rise in the surface temperature of the Earth. Global warming is one of the names given to the systematic increase of globally averaged surface temperature that has been measured since the mid-nineteenth century. There is abundant evidence that…

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 phaneritic (visibly crystalline) plutonic rock composed chiefly of sodic plagioclase (oligoclase or andesine), alkali feldspar (microcline or orthoclase, usually perthitic), quartz, and subordinate dark-colored (mafic) minerals (biotite,…

A strongly cemented or hardened (indurated) dark gray sandstone that is characterized by abundant dark-colored detrital rock fragments and more than 15% clay minerals (matrix) between sand grains. The term graywacke evolved from initially informal…

The most common sulfate mineral, characterized by the chemical formula CaSO4 · 2H2O; it shows little variation from this composition.Gypsum is one of the several evaporite minerals. This mineral group includes chlorides, carbonates, borates,…

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 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…

A metamorphic rock that has been subjected to heating during contact metamorphism around intrusive igneous rocks. Hornfels is typically fine-grained, although where it is subjected to high temperatures, large crystals called porphyroblasts can form.…

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.…

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,…

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…

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 naturally occurring geologic body that may contain one or more metals. The metals may be present as native elements, or, more commonly, as oxides, sulfides, sulfates, silicates, or other compounds. The term ore is often used loosely to include…

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 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…

The evolving internet technologies for content sharing and collaborating among communities of online users. Since the advent of the Web 2.0—the more dynamic and interactive second generation of the World Wide Web—the term social media has become…

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…