biology-dictionary_11-06-2009

Electric potential The difference in the amount of electric charge between a region of positive charge and a region of negative ...

Electron microscope (EM) A microscope that focuses an electron beam through a specimen, resulting in resolving power a thousandf ...

Encystment The process of forming or becoming enclosed in a cyst or capsule. Endarch xylem A primary xylem strand in which the f ...

Endodermis The innermost layer of the cortex in plant roots; a cylinder one cell thick that forms the boundary between the corte ...

Endosymbiotic theory A hypothesis about the origin of the eukaryotic cell, maintaining that the forerunners of eukaryotic cells ...

Enzyme A class of proteins serving as catalysts, chemical agents that change the rate of a reaction without being consumed by th ...

Epigenesis A cartilaginous flap that blocks the top of the windpipe, the glottis, during swallowing, which prevents the entry of ...

Equilibrium species Species characterized by low reproduction rates, long development times, large body size, and long adult lif ...

Estivation A physiological state characterized by slow metabolism and inactivity, which permits survival during long periods of ...

Eukaryote An organism whose cells contain membraine-bound organelles and whose DNA is enclosed in a cell nucleus and is associat ...

Excitatory postsynaptic potential (EPSP) An electrical change (depolarization) in the membrane of a postsynaptic neuron caused b ...

Exotoxin A toxic protein secreted by a bacterial cell that produces specific symptoms even in the absence of the bacterium. Exot ...

F F 1 (first filial generation) The first filial or hybrid offspring in a genetic cross-fertilization. F 2 (second filial genera ...

Family A taxonomic grouping of related, similar genera; the category below order and above genus. Fat A biological compound cons ...

Fibrin The activated form of the blood-clotting protein fibrinogen, which aggregates into threads that form the fabric of the cl ...

Fitness The genetic contribution of an individual to succeeding generations relative to the contributions of other individuals i ...

Follicle-stimulating hormone (FSH) A protein hormone secreted by the anterior pituitary that stimulates the production of eggs b ...

Frameshift mutation A mutation occurring when the number of nucleotides inserted or deleted is not a multiple of 3, thus resulti ...

G Gases An aeriform fluid that possesses complete molecular mobility and the property of indefinite expansion. A gas has no defi ...

Gametangium The reproductive organ of bryophytes, consisting of the male antheridium and female archegonium; a multichambered ja ...