Biology Glossary

A heritable trait or characteristic that has evolved through natural selection because it enhances an organism's fitness in its particular environment.

One of two or more alternative forms of a gene that occupy the same locus on a chromosome and can produce different phenotypic effects.

An organic molecule containing an amino group and a carboxyl group that serves as the building block of proteins, with 20 standard types encoded by the genetic code.

The pathway through which a chemical element or molecule moves through the biotic and abiotic compartments of Earth, such as the carbon, nitrogen, and water cycles.

A large-scale ecological community defined by its dominant vegetation type and climate, such as tropical rainforest, desert, tundra, or temperate grassland.

The fundamental structural and functional unit of all living organisms, bounded by a membrane and capable of carrying out the basic processes of life.

A thread-like structure of tightly coiled DNA and histone proteins found in the nucleus of eukaryotic cells that carries genetic information in the form of genes.

A sequence of three consecutive nucleotides in messenger RNA that specifies a particular amino acid or a stop signal during protein synthesis.

The gel-like substance enclosed within the cell membrane, excluding the nucleus, that contains organelles, enzymes, and various molecules necessary for cellular processes.

The passive movement of molecules or ions from a region of higher concentration to a region of lower concentration, driven by the kinetic energy of the particles.

An allele that expresses its phenotypic effect even when present in a heterozygous combination with a different allele at the same genetic locus.

A network of membranous tubules and sacs within eukaryotic cells that functions in protein processing (rough ER) and lipid synthesis (smooth ER).

The change in the inherited characteristics of biological populations over successive generations, driven by mechanisms including natural selection, genetic drift, mutation, and gene flow.

A complex network of interconnected food chains within an ecosystem that illustrates the multiple feeding relationships among producers, consumers, and decomposers.

A mature reproductive cell (sperm or egg) that is haploid, containing half the number of chromosomes of the organism, and fuses with another gamete during fertilization.

The metabolic pathway occurring in the cytoplasm that breaks down one molecule of glucose into two molecules of pyruvate, yielding a net gain of two ATP and two NADH.

The natural environment or ecological area in which a particular species lives, characterized by specific physical and biological conditions that support its survival.

A diverse group of hydrophobic organic molecules, including fats, oils, phospholipids, and steroids, that serve as energy storage, structural components of membranes, and signaling molecules.

The monomer unit of nucleic acids, consisting of a nitrogenous base, a five-carbon sugar (ribose or deoxyribose), and one or more phosphate groups.

A specialized membrane-bound structure within a eukaryotic cell that performs a specific function, such as the nucleus, mitochondria, or endoplasmic reticulum.

The passive movement of water molecules across a selectively permeable membrane from a region of lower solute concentration to a region of higher solute concentration.

The study of evolutionary relationships among biological entities, often depicted as branching tree diagrams called phylogenies based on molecular and morphological data.

An allele whose phenotypic effect is masked in the heterozygous condition and is only expressed when the organism is homozygous for that allele.

The branch of biology concerned with the classification, naming, and identification of organisms into hierarchical groups such as domain, kingdom, phylum, class, order, family, genus, and species.

A diploid cell formed by the fusion of two haploid gametes during fertilization, representing the earliest stage of development of a new organism.