ABO blood groups Blood group antibodies (A, B, AB, O) that may destroy red blood cells bearing the antigen to which they are directed; also called "agglutinins." These red-cell antigens are the phenotypic expression of inherited genes, and the frequency of the four main groups varies in populations throughout the world. The antigens of the […]

Aerobic To Algae (singular, alga) (Biology)

Aerobic Any organism, environmental condition, or cellular process that requires atmospheric oxygen. Aerobic microorganisms, called aerobes, require the presence of oxygen for growth. An aerobe is capable of using oxygen as a terminal electron acceptor and can tolerate oxygen levels higher than that present in the air (21 percent oxygen). They have a respiratory type […]

Allantois To Amino acid (Biology)

Allantois During the embryonic stage of mammals, birds, and reptiles, the allantois, a small sac, is one of four extra-embryonic membranes (along with amnion, yolk sac, chorion) and serves several functions, such as a repository for the embryo’s nitrogenous waste (chiefly uric acid) in reptiles and birds (in the egg). The allan-tois provides oxygen to […]

Amino acid residue (in a polypeptide) To Anation (Biology)

Amino acid residue (in a polypeptide) When two or more amino acids combine to form a peptide, the elements of water are removed, and what remains of each amino acid is called amino acid residue. Amino acid residues are therefore structures that lack a hydrogen atom of the amino group (-NH-CHR-COOH), or the hydroxy moiety […]

Androgens To Anticodon (Biology)

Androgens Steroid sex hormones, such as testosterone secreted by the testes in males, and others secreted by the adrenal cortex in humans and higher animals, as well as by the adrenal glands and ovaries in mammals. Androgens stimulate the development and maintenance of the male reproductive system such as sperm production, sexual behavior, and muscle […]

Antidiuretic hormone (ADH) To Arrhenius, Svante August (Biology)

Antidiuretic hormone (ADH) Also known as vaso-pressin, ADH is a nine-amino acid peptide secreted from the posterior pituitary gland. The hormone is packaged in secretory vesicles with a carrier protein called neuro-physin within hypothalamic neurons, and both are released upon hormone secretion. The single most important effect of antidiuretic hormone is to conserve body water […]

Arteriosclerosis To Bacterium (plural, bacteria) (Biology)

Arteriosclerosis Also known as "hardening of the arteries." It is a disease whereby the arteries thicken and the inner surfaces accumulate deposits of hard plaques of cholesterol, calcium, fibrin, and other cellular debris. The arteries become inelastic and narrowed, which increases the stress on the heart as it pumps blood through, and complete obstruction with […]

Balanced polymorphism To Binding site (Biology)

Balanced polymorphism The maintenance of two or more alleles in a population due to the selective advantage of the heterozygote. A heterozygote is a genotype consisting of two different alleles of a gene for a particular trait (Aa). Balanced polymorphism is a type of polymorphism where the frequencies of the coexisting forms do not change […]

Binomial (binomial name) To Blood (Biology)

Binomial (binomial name) Each organism is named using a Latin-based code consisting of a combination of two names, the first being a generic (genus) name and the second a specific trivial name, which, together,constitute the scientific name of a species. Lupinus perennis, or wild blue lupine, is an example. Both names are italicized, and both […]

Blood-brain barrier (BBB) To Blood pressure (Biology)

Blood-brain barrier (BBB) The blood-brain barrier is a collection of cells that press together to block many substances from entering the brain while allowing others to pass. It is a specialized arrangement of brain capillaries that restricts the passage of most substances into the brain, thereby preventing dramatic fluctuations in the brain’s environment. It maintains […]