Search Results

An annual plant (seldom perennial) of the genus Amaranthus (family Amaranthaceae) that is distributed worldwide in warm and humid regions. Amaranth plants are botanically distinguished by their small chaffy flowers (see illustration), which are…

Most commonly, a generic name for all fossil resins, although it has been restricted by some to refer only to succinite, the mineralogical species of fossil resin that includes most of the Baltic Coast deposits. Resins generally are complex mixtures…

The transparent purple to violet variety of the mineral quartz. Although quartz is perhaps the commonest gem mineral known, amethyst is rare in the deep colors that characterize fine quality. Amethyst is usually colored unevenly and is often heated…

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.…

Determination of the relative or absolute age of materials or objects by measurement of the degree of racemization of the amino acids present. With the exception of glycine, the amino acids found in proteins can exist in two isomeric forms called d-…

A thin, cellular, extraembryonic membrane forming a closed sac which surrounds the embryo in all reptiles, birds, and mammals and is present only in these forms; hence the collective term amniotes is applied to these animals. The amnion contains a…

A collective term for the classes Reptilia (reptiles), Aves (birds), and Mammalia (mammals) of the subphylum Vertebrata. The remaining vertebrates, including the several classes of fishes and the amphibians, are grouped together as the Anamnia.…

An enzyme that is essential for maintenance of cellular energy balance. All living cells carry out many energy-requiring processes, including growth and division, movement, and uptake of nutrients from their environment. To achieve this, they…

A stimulating drug that affects the brain and the body. Amphetamine is a stimulant of the central nervous system. Chemically, amphetamine is a racemic mixture of the l and d isomers of α-methyl-β-phenethylamine (see illustration). The l isomer has…

A disorder characterized by the accumulation of an unusual extracellular fibrous protein (amyloid) in the connective tissue of the body. The deposition of amyloid may be widespread, involving major organs and leading to serious clinical…