Science / Biology Glossary

Adenosine Diphosphate (ADP): Lower energy form of ATP, having two (instead of the three in ATP) phosphhate groups attached to the adenine base and ribose sugar.

Adenosine Triphosphate (ATP): A common form in which energy is stored in living systems; consists of a nucleotide (with ribose sugar) with three phosphate groups. The energy coin of the cell.

Adhesion: The ability of molecules of one substance to adhere to a different substance.

Adrenocorticotropic Hormone (ACTH): A hormone produced by the anterior pituitary that stimulates the adrenal cortex to release several hormones including cortisol.

Adventitious Roots: Roots that develop from the stem following the death of the primary root. Branches from the adventitious roots form a fibrous root system in which all roots are about the same size; occur in . . . View Full Definition

Age Structure: The relative proportion of individuals in each age group in a population.

Aggregates: Fairly random associations of animals with little or no internal organization; form in response to a single stimulus and disperse when the stimulus is removed; one of the three broad classes . . . View Full Definition

Albinism: Genetic condition caused by the bodys inability to manufacture pigments; an autosomal recessive trait.

Aldosterone: A hormone secreted by the adrenal glands that controls the reabsorption of sodium in the renal tubule of the nephron.

Alleles: Alternate forms of a gene.

Allergens: Antigens that provoke an allergic reaction.

Alpha Decay: Type of radioactive decay in which a radioisotope emits a large but slow-moving particle consisting of two protons and two neutrons.

Alternation Of Generations: A life cycle in which a multicellular diploid stage is followed by a haploid stage and so on; found in land plants and many algae and fungi.

Altitudinal Gradient: As altitude increases, a gradient of cooler, drier conditions occurs.

Alveoli: Tiny, thin-walled, inflatable sacs in the lungs where oxygen and carbon dioxide are exchanged.

Amensalism: A symbiotic relationship in which members of one population inhibit the growth of another population without being affected.

Amino Acid Sequence: Also known as the primary structure of a protein/polypeptide; the sequence of amino acids in a protein/polypeptide controlled by the sequence of DNA bases.

Amino Acids: The subunits (monomers) from which proteins (polymers) are assembled. Each amino acid consists of an amino functional group, and a carboxyl acid group, and differs from other amino acids by . . . View Full Definition

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