E

earlywood The large, thin-walled xylem cells produced early in the growing season, which appear less dense than latewood.

eccrine Applies to a type of mammalian sweat gland that produces a watery secretion.

ecdysiotropin Hormone secreted in brain of insects that stimulates prothoracic gland to secrete molting hormone. Prothoracicotropic hormone; brain hormone.

ecdysis (1) The shedding of the arthropod exoskeleton to accommodate increased body size or a change in morphology (as may occur in molting from immature to adult); to molt; may also refer to the shedding of the outer epidermis of the skin of reptiles. (2) The shedding of the cuticle in aschelminths in order to grow. Also called molting.

ecdysone Molting hormone of arthropods, stimulates growth and ecdysis, produced by prothoracic glands in insects and Y organs in crustaceans.

Echinodermata The phylum of coelomate animals whose members are pentaradially symmetrical as adults and possess an endoskeleton covered by epithelium and a water-vascular system. Sea stars, sea urchins, sea cucumbers, sea lilies.

echinoderms Invertebrates with radial symmetry and a water vascular system.

Echinoidea The class of echinoderms whose members are globular or disk shaped, possess moveable spines, and a skeleton of closely fitting plates. Sea urchins and sand dollars.

Echiura A phylum of protostomate, marine animals whose members burrow in mud or sand or live in rock crevices. They possess a spatula-shaped proboscis and are 15 to 50 cm in length. Spoon worms.

echiurans Burrowing invertebrates that have an unsegmented body and a non-retractable proboscis.

echolocation A method of locating objects by determining the time it takes for an echo to return and the direction from which it returns. As in bat echolocation.

eclipsed antigen Antigen borne by the parasite that is common to both the host and the parasite but that genetically is of parasite origin.

eclosion The process whereby the adult form of an insect emerges from the pupa.

ecocentric A philosophy that claims moral values and rights for both organisms and ecological systems and processes.

ecocline The gradient between adjacent biomes; a gradient of environmental conditions.

ecofeminism A pluralistic, nonhierarchical, relationship-oriented philosophy that suggests how humans could reconceive themselves and their relationships to nature in nondominating ways as an alternative to patriarchal systems of domination.

ecojustice Justice in the social order and integrity in the natural order.

ecological adaptation Short-term changing responses expressed by an individual organism to its environment.

ecological development A gradual process of environmental modification by organisms.

ecological equivalents Different species that occupy similar ecological niches in similar ecosystems in different parts of the world.

ecological niche The functional role and position of a species (population) within a community or ecosystem, including what resources it uses, how and when it uses the resources, and how it interacts with other populations.

ecological pyramid of biomass Total biomass of all organisms at each trophic level in a food chain; typically biomass declines with successively higher trophic levels.

ecological pyramid of energy Total energy content of all organisms at each trophic level in a food chain; since only 5%_20% of energy is passed between trophic levels; energy content declines at successively higher trophic levels.

ecological pyramid of numbers Number of organisms supported at each trophic level in a food chain; typically, fewer organisms are supported at successively higher trophic levels.

ecological succession The sequential replacement of one vegetative community by another through a series of stages; succession ends when the climax community is established.

ecology The scientific study of relationships between organisms and their environment. It is concerned with the life histories, distribution, and behavior of individual species as well as the structure and function of natural systems at the level of populations, communities, and ecosystems.

economic defendability Defense of a resource that yields benefits that outweigh the costs of defending it.

economic development A rise in real income per person; usually associated with new technology that increases productivity or resources.

economic growth An increase in the total wealth of a nation; if population grows faster than the economy, there may be real economic growth, but the share per person may decline.

economic sanctions Using the threat or action of withholding food, medical care, or other critical societal needs to force compliance with one's policies.

ecosystem An ecological unit consisting of both the biotic communities and the nonliving (abiotic) environment, which interact to produce a stable system.

ecosystem management An integration of ecological, economic, and social goals in a unified systems approach to resource management.

ecosystem restoration To reinstate an entire community of organisms to as near its natural condition as possible.

ecotage Direct action (guerrilla warfare) or sabotage in defense of nature; also called monkey wrenching.

ecotone The transition zone between two adjacent communities.

ecotourism A combination of adventure travel, cultural exploration, and nature appreciation in wild settings.

ectocommensal Commensal symbiont that lives on the outer surface of its host.

ectoderm Outer layer of cells of an early embryo (gastrula stage); one of the germ layers, also sometimes used to include tissues derived from ectoderm.

ectognathous Derived character of most insects; mandibles and maxillae not in pouches.

ectolecitha l Yolk for nutrition of the embryo contributed by cells that are separate from the egg cell and are combined with the zygote by envelopment within the eggshell.

ectomycorrhizae Association of a fungus with a vascular plant root or rhizome system in which the fungus surrounds, but does not penetrate the living cells (protoplast) of the system.

ectoneural Oral (chief) nervous system in echinoderms.

ectoparasite Parasite that lives on the outer surface of its host.

ectopic Infection in a location other than normal or expected.

ectoplasm The cortex of a cell or that part of cytoplasm just under the cell surface; contrasts with endoplasm.

Ectoprocta A phylum of animals whose members are colonial and fresh water or marine. Anus ends outside a ring of tentacles. Lophophore used in feeding. Moss animals or bryozoans.

ectoprocts See bryozoans.

ectotherm An organism whose internal temperature varies with that of the environment. Compare endotherm.

ectothermic Having a variable body temperature derived from heat acquired from the environment; contrasts with endothermic.

ectotympanic ecto = outer; tympani = a drum.

edema Escape of fluid from blood into interstitial space, causing swelling.

edge effects A change in species composition, physical conditions, or other ecological factors at the boundary between two ecosystems. Some organisms flourish at this boundary and benefit from processes such as habitat fragmentation that increase edge area. Other organisms are harmed by increasing edge effects.

effector An organ, tissue, or cell that becomes active in response to stimulation.

efferent Leading or conveying away from some organ, for example, nerve impulses conducted away from the brain, or blood conveyed away from an organ; contrasts with afferent.

effluent sewerage A low-cost alternative sewage treatment for cities in poor countries that combines some features of septic systems and centralized municipal treatment systems. A septic tank near each residence collects and processes solid wastes_and must be pumped periodically just like a septic tank_while liquid effluent is collected and piped to a central treatment plant. This avoids drainfields in urban areas and yet allows sewer pipes and treatment plants to be downsized, saving money.

egestion Act of casting out indigestible or waste matter from the body by any normal route.

egestion vacuole A membrane-bound vesicle within the cytoplasm of a protist that functions in expelling wastes.

egg The middle of three haploid cells at the micropylar end of the embryo sac; when fertilized, it will form the zygote.

egg apparatus Egg cell and adjacent synergids in the embryo sac (female gametophyte) of angiosperms.

Ekman spiral The spiral change in the movement of water in the water column when the water is pushed by wind. The Ekman layer is that part of the water column affected by wind; Ekman transport is the net water movement 90from the wind direction.

El Nino A climatic change marked by shifting of a large warm water pool from the western Pacific Ocean towards the east. Nutrient-rich upwelling currents along the coast of South America are blocked by this sea change and fisheries fail catastrophically. An El Niño event normally is accompanied by droughts in Australia and Southeast Asia together with heavy rain and snow in western North America.

El Nino_Southern Oscillation (ENSO) Large-scale changes in the normal weather patterns of the Pacific basin and adjacent regions. El Niño is a warming of the surface currents in the eastern Pacific, only one of the many consequences of ENSO.

elaters The spiral walls that aid in the release and dispersal of spores from the sporangia in horsetails (Equisetum) or the elongate, hygroscopic cells with spiral wall thickenings that aid in the release of spores in liverworts.

electrical synapse A synapse at which local currents resulting from electrical activity flow between the two neurons through gap junctions joining them.

electrode stimulation The stimulation of a neuron by artificially depolarizing the membrane with an electrode.

electrolyte A substance that dissociates into ions when fused or in solution and thus becomes capable of conducting electricity; an ionic solute.

electromagnetic spectrum The entire radiation spectrum from the high-energy levels of cosmic rays to the low-energy levels of radiowaves; a small portion in the center provides wavelengths visible to humans.

electron A small, negatively charged particle that revolves around the nucleus of an atom. It has a very low mass.

electron transfer The process of energy transfer in biological systems, usually in small steps with only slight changes in energy levels.

electron transport chain In a cell membrane, electron carriers and enzymes positioned in an organized array that enhance oxidation-reduction reactions; such systems function in the release of energy that is used in ATP formation and other reactions.

Electron Transport System The final stage of respiration; a series of enzymes and coenzymes on the inner membrane of mitochondria functioning in the transfer of electrons and the resulting synthesis of ATP.

electrophoresis The separation of different proteins or nucleic acids within a gel matrix that is subjected to an electric field; separation is based on size and/or charge of the molecule(s).

electroreception The ability to detect weak electrical fields in the environment.

electroreceptor A receptor that senses changes in an electrical current usually in the surrounding water; also called an ampullary organ.

electrostatic precipitators The most common particulate controls in power plants; fly ash particles pick up an electrostatic surface charge as they pass between large electrodes in the effluent stream, causing particles to migrate to the oppositely charged plate.

element Building blocks of matter that cannot be broken down into a simpler substance. Each element is composed of just one type of atom.

eleocyte Fat-containing cells in annelids that originate from the chlorogogen tissue.

elephantiasis Disfiguring condition caused by chronic infection with filarial worms Wuchereria bancrofti and Brugia malayi.

Ellipsoidal Elliptical shape.

elver a juvenile eel

embryo The early developmental stage that, through embryological development, ultimately becomes an adult individual. In plants, that portion of a seed that will form the growing seedling following germination; it has a radicle, apical meristem, and embryonic leaf or leaves.

embryogenesis The origin and development of the embryo; embryogeny.

embryology The study of development from the egg to the point that all major organ systems have formed.

embryonic axis The main root/shoot body of a seedling.

embryonic diapause The arresting of early development to allow young to hatch, or be born, when environmental conditions favor survival.

embryophore In reference to the eggshell of many cestodes, that portion contributed by the inner envelope, derived from embryonic blastomeres.

embryo sac Female gametophyte of angiosperms; it is retained within the ovule.

emergence The appearance of properties in a biological system (at the molecular, cellular, organismal, or species levels) that cannot be deduced from knowledge of the component parts taken separately or in partial combinations; such properties are termed emergent properties.

emergent plant community Marine plant community in which most leafy growth occurs above sea level.

emigrate To move from one area to another to take up residence.

emigration The movement of members from a population.

emission standards Regulations for restricting the amounts of air pollutants that can be released from specific point sources.

emphysema An irreversible, obstructive lung disease in which airways become permanently constricted and alveoli are damaged or destroyed.

Emulsify To produce small droplets of a liquid.

emulsion A colloidal system in which both phases are liquids.

encephalitis Infection of the brain, especially by viruses or amebas.

encrusting Describing an organism that grows as a crust over rocks and other hard surfaces.

encystment The secretion of a protective outer covering that permits some small invertebrates to withstand exposure to extreme environmental stresses, such as desiccation and overcrowding.

end bulb A tiny swelling on the terminal end of telodendria at the distal end of an axon; also called the synaptic bouton.

end-product (feedback) inhibition The inhibition of the first enzyme in a pathway by the end product of that pathway.

endangered species A living species that is in danger of becoming extinct because of small population sizes, poor reproduction, reduced available habitat, or a combination of these factors.

endemic Peculiar to a certain region or country; native to a restricted area; not introduced.

endemism A state in which species are restricted to a single region.

endemnicity Amount or severity of a disease in a particular geographic area.

endergonic Used in reference to a chemical reaction that requires energy; energy absorbing.

endergonic reaction Chemical reaction that requires energy.

endite Medial process on an arthropod limb.

endocarp Innermost layer of the pericarp (fruit wall).

endochondral Occurring with the substance of cartilage, especially bone formation.

endocommensal Commensal symbiont that lives inside its host.

endocrine glands A series of ductless glands in both invertebrates and vertebrates that release hormones into the body through the blood or lymph.

endocrine A system of ductless glands secreting hormones into the bloodstream and targeting another organ to produce a response.

endocrinology The study of the endocrine system and its role in the physiology of an animal.

endocytosis Ingestion of particulate matter or fluid by phagocytosis or pinocytosis; that is, bringing material into a cell by invagination of its surface membrane and then pinching off the invaginated portion of a vacuole.

endoderm Deep primary germ layer of the embryo. It gives rise to the linings of the pharynx, respiratory tree, digestive tract, urinary bladder, and the urethra.

endodermis Innermost layer of the root cortex surrounding the stele; many of the endodermal cells have Casparian strips.

endodyogeny Same as endopolyogeny except that only two daughter cells are formed.

endogenous Processes within the animal; used here with particular reference to the internal, genetically based, components of biological rhythms.

endogenous clock mechanism Any internal processes that are genetically based and that play a role in setting or regulating biological rhythms.

endogenous factors Internal factors regulating an organism's growth and development.

endognathous Ancestral character in insects, found in orders Diplura, Collembola, and Protura, in which the mandibles and maxillae are located in pouches.

endolecithal Yolk for nutrition of the embryo incorporated into the egg cell itself.

endolithic alga An alga that burrows into calcareous rocks or corals.

endolymph Fluid that fills most of the membranous labyrinth of the vertebrate ear.

endometrium The lining of the uterus; during the reproductive years, this layer is sloughed each month during menstruation.

endomycorrhizae Association of a fungus with a vascular plant root or rhizome system in which the fungus penetrates the living cells of the root.

endoparasite Parasite that lives inside its host.

endophyte A plant that lives within the tissues of another plant.

endoplasm The portion of cytoplasm that immediately surrounds the nucleus.

endoplasmic reticulum Cytoplasmic organelle composed of a system of interconnected membranous tubules and vesicles; ER; rough ER has ribosomes attached to the side of the membrane facing the cytoplasm and smooth ER does not. Rough ER functions in protein synthesis while smooth ER functions in lipid synthesis.

endopod, endopodite Medial branch of a biramous crustacean appendage(phylum Arthropoda).

endopolyogeny Formation of daughter cells, each surrounded by its own membrane, while still in the mother cell.

endopterygote Condition of internal wing bud development in an insect. Also, an insect in which the wing buds develop externally or any insect secondarily wingless but derived from such an ancestor; associated with holometabolous insects.

endorphin (contraction of endogenous morphine). Group of opiate-like brain neuropeptides that modulate pain perception and are implicated in many other functions.

endoskeleton A skeleton that lies beneath the surface of the body (e.g., the bony skeleton of vertebrates and the calcium carbonate skeleton of echinoderms); contrasts with exoskeleton.

endosome Nucleolus in nucleus of some protozoa that retains its identity through mitosis.

endosperm A triploid nutritive tissue resulting from the fusion of a haploid sperm nucleus with the two haploid polar nuclei in the ovule of angiosperms.

endostyle Ciliated groove(s) in the floor of the pharynx of tunicates, cephalochordates, and larval jawless fishes useful for accumulating and moving food particles to the stomach.

endosymbiont hypothesis The idea whereby the evolution of the eukaryotic cell might have occurred when a large anaerobic amoeboid prokaryote ingested small aerobic bacteria and stabilized them instead of digesting them.

endosymbiosis The theory that some cellular organelles arose by the incorporation of a prokaryote into the cytoplasm of a eukaryote.

Endothelium A layer of epithelial cells forming a tissue that lines the circulatory system and body cavities; derived from the mesoderm of the embryo.

endotherm (or homeotherm)An organism that can regulate its internal temperature. Compare ectotherm.

endothermic Having a body temperature determined by heat derived from the animal's own oxidative metabolism; contrasts with ectothermic.

energy budget An accounting of the way in which energy coming into an ecosystem from the sun is lost or processed by organisms of the ecosystem.

energy efficiency A measure of energy produced compared to energy consumed.

energy pyramid A representation of the loss of useful energy at each step in a food chain.

energy recovery Incineration of solid waste to produce useful energy.

energy The capacity to do work (that is, to change the physical state or motion of an object).

energy-level shell The distribution of electrons around the nucleus of an atom.

engram (memory trace)The physical manifestation of learning; neural mechanism for storage of information that involves structural synaptic changes and/or chemical changes.

enkephalin Group of small brain neuropeptides with opiate-like qualities.

enrichment experiments Experimental manipulations that involve providing organisms with particular types of stimuli (e.g., social, sensory, motor) to ascertain the effects later in development.

enterocoel A type of coelom formed by the outpouching of a mesodermal sac from the endoderm of the primitive gut.

enterocoelic mesoderm formation Embryonic formation of mesoderm by a pouchlike outfolding from the archenteron, which then expands and obliterates the blastocoel, thus forming a large cavity, the coelom, lined with mesoderm.

enterocoelomate An animal having an enterocoel, such as an echinoderm or a vertebrate.

enterocoely Formation of a coelom through outpocketing of the inner portion of the archenteron in some animals (deuterostomes).

enteron The digestive cavity.

Enteropneusta A class of hemichordates whose members live in burrows in shallow marine water. Their bodies are divided into three regions: proboscis, collar, and trunk. Acorn worms.

entine The inner layer of a pollen grain shell.

entire A smooth leaf margin without teeth, lobes, or undulations.

entomology Study of insects.

Entoprocta A phylum of aschelminths commonly called entoprocts.

entozoic Living within another animal; internally parasitic (chiefly parasitic worms).

entrainment The process by which a biological clock is set or reset by synchronizing with the period of some external, environmental stimulus.

entropy A measure of the degree of disorganization of a system; how much energy in a system has become so dispersed (usually as heat) so that it is no longer available to do work. The higher the entropy, the more the disorder.

environment The circumstances or conditions that surround an organism or group of organisms as well as the complex of social or cultural conditions that affect an individual or community.

environmental ethics A search for moral values and ethical principles in human relations with the natural world.

environmental hormones Chemical pollutants that substitute for, or interfere with, naturally-occurring hormones in our bodies; these chemicals may trigger reproductive failure, developmental abnormalities, or tumor promotion.

environmental impact statement (EIS) An analysis, required by provisions in the National Environmental Policy Act of 1970, of the effects of any major program a federal agency plans to undertake.

environmental insults Any factor in the physical environment that inhibits the growth and/or development of an organism.

environmental justice Combines civil rights with environmental protection to demand a safe, healthy, life-giving environment for everyone.

environmental literacy Fluency in the principles of ecology that gives us a working knowledge of the basic grammar and underlying syntax of environmental wisdom.

environmental resistance All the limiting factors that tend to reduce population growth rates and set the maximum allowable population size or carrying capacity of an ecosystem.

environmental resources Anything an organism needs that can be taken from the environment.

environmental science The systematic, scientific study of our environment as well as our role in it.

environmental terrorism Conducting acts of terrorism through the destruction or pollution of the environment.

environmentalism Active participation in attempts to solve environmental pollution and resource problems.

enzyme A substance, produced by living cells, that is capable of speeding up specific chemical transformations, such as hydrolysis, oxidation, or reduction, but is unaltered itself in the process; a biological catalyst.

enzyme-linked immunosorbent assay (ELISA) Immunodiagnostic test designed to detect the presence of fixed antibody through linkage with an enzymatic reaction.

enzymes Molecules, usually proteins or nucleic acids, that act as catalysts in biochemical reactions.

enzyme-substrate complex The binding of a substrate molecule to the active site of an enzyme.

ocytes A group of prokaryotes currently classified among the Archaebacteria but possibly a sister group of eukaryotes.

eosinophil White blood cells characterized by the presence of cytoplasmic granules that become stained by an acid dye.

eosinophilia Elevated eosinophil count in the circulating blood; commonly associated with chronic parasite infections.

ephemeral Temporary, such as vegetation that completes its life cycle in a short time.

ephyra Refers to castlelike appearance.Miniature medusae produced by asexual budding of a scyphistoma (class Scyphoza, phylum Cnidaria). Ephyrae mature into sexually mature medusae.

epi G. A prefix meaning on, upon, or over.

epiblast An outer layer of cells in the embryo of an amniote that forms from the proliferation and movement of cells of the blastoderm.

epiboly A spreading and thinning of ectoderm from the animal pole of an amphibian gastrula toward the vegetal pole.

epicaridium First larval stage of the isopod suborder Epicaridea; attaches to a free-living copepod.

Epicondyle epi = above; condyl a knuckle.

epicotyl Portion of the shoot of an angiosperm embryo or seedling above the cotyledons.

epicuticle Thin, outermost layer of arthropod cuticle; contains sclerotin but not chitin.

epicycle See ultradian rhythm.

epidemic Sharp rise in the incidence of an infection or disease.

epidemic hemorrhagic fever Virus disease transmitted by mosquitoes. Also called dengue.

epidemiology Study concerned with all ecological aspects of a disease to explain its transmission, distribution, prevalence, and incidence.

epidemiology The study of the distribution and causes of disease and injuries in human populations.

Epidermal epi = above; derma = skin.

epidermis The outer, nonvascular layer of skin of ectodermal origin; in invertebrates, a single layer of ectodermal epithelium.

epididymis Part of the sperm duct that is coiled and lying near the testis.

epifauna Animals that live on the surface of the substrate. Compare infauna.

epigenesis The embryological (and generally accepted) view that an embryo is a new creation that develops and differentiates step by step from an initial stage; the progressive production of new parts that were nonexistent as such in the original zygote.

epigenetics Study of the relationship between genotype and phenotype as mediated by developmental processes.

epigynous Floral parts (sepals, petals, and stamens) appear to arise from the top of an ovary; the ovary is said to be inferior.

epimastigote Trypanosomatid flagellate similar to a promastigote but with a short undulating membrane, such as in Blastocrithidia.

epinasty The unequal growth of petioles causing the leaf blade to curve downward.

epipelagic zone The pelagic environment from the surface to a depth of 100 to 200 m (350 to 650 ft).

epiphysealdisk A cartilaginous growth line at the ends of long bones.

epiphyte Plant that grows on top of another plant for support and position, but derives no nutrition from the host.

epipod, epipodite A lateral process on the protopod of a crustacean appendage, often modified as a gill.

epistasis Prevention of expression of an allele at one locus by an allele at another locus.

epistome Flap over the mouth in some lophophorates bearing the protocoel.

epitheca the larger portion of a diatom frustule

epithelial tissue The cellular covering of internal and external surfaces of the body; consists of cells joined by small amounts of cementing substances. Epithelium is classified into types based on the number of layers deep and the shape of the superficial cells.

epithelium A cellular tissue covering a free surface or lining a tube or cavity.

epitoke Posterior part of a marine polychaete when swollen with developing gonads during the breeding season; contrast with atoke.

epitoky The formation of a reproductive individual (epitoke) that differs from the nonreproductive (atoke) form of that species.

epitope Antigenic determinant; the portion of the antigen molecule displayed on the surface of an antigen-presenting cell (APC).

epizootic Massive infection rate among animals other than humans; identical to an epidemic in humans.

equation With respect to comparative learning, the attempts to match situations and procedures for examining learning behavior in different species.

equatorial currents Major ocean currents that move parallel to the Equator.

equilibrium community Also called a disclimax community; a community subject to periodic disruptions, usually by fire, that prevent it from reaching a climax stage.

ergosterol The most common sterol; can be converted to vitamin D in the skin of animals exposed to sunlight.

ergot The spore-producing reproductive body of a fungus that infects grain crops; ergot contains lysergic acid and ergonovine.

erythroblastosis fetalis A disease of newborn infants caused when Rh-negative mothers develop antibodies against the Rh-positive blood of the fetus. See blood type.

erythrocyte Red blood cell; has hemoglobin to carry oxygen from lungs or gills to tissues; during formation in mammals, erythrocytes lose their nuclei, those of other vertebrates retain the nuclei.

esophagus The passage extending from the pharynx to the stomach.

espundia Disease caused by Leishmania braziliensis. Also called chiclero ulcer, uta, pian bois, or mucocutaneous leishmaniasis.

essential amino acid Amino acid that cannot be synthesized by an organism but must be obtained ready-made in the diet for proper health.

essential nutrient Nutrient that cannot be synthesized by an organism but must be obtained ready-made in the diet for proper health.

essential oils Highly volatile and aromatic oils formed in glands or special cells by some plants; probably involved in pollinator attraction or repulsion of herbivores; used in perfumes, soaps, medicine, and food.

esthete Light sensory receptor on a shell of a chiton (phylum Mollusca).

estrogen The female sex hormone in vertebrates.

estrone An animal steroid found in some plants in low concentration.

estrous The period of highest sexual receptivity (or "heat") in some female mammals that coincides with the time of egg release by the ovarymarked by intense sexual urges.

estrus cycle A recurrent series of changes in the reproductive physiology of female mammals other than primates; females are receptive, physiologically and behaviorally, to the male only at certain times in this cycle.

estuary A bay or drowned valley where a river empties into the sea. Fresh water mingling with salt water brings in sediment and nutrients and creates a gradient of salinity that makes estuaries among the most diverse and biologically productive ecosystems on earth.

ethanol Ethyl alcohol is the end product of anaerobic respiration (fermentation) in plants.

ethmoid Like a sieve.

ethogram An inventory of all of the behavior patterns of a species.

ethologist A person who studies the whole patterns of animal behavior in natural environments, stressing the analysis of adaptation and the evolution of the patterns.

ethology The study of whole patterns of animal behavior in natural environments, stressing the analysis of adaptation and the evolution of the patterns.

ethylene Gaseous plant hormone involved in fruit ripening and other aspects of plant growth and development.

etiolation The abnormal elongation of stems caused by insufficient light or unbalanced hormonal relationships. Etiolated stems often lack chlorophyll.

eucaryotes cells characterized by an organized nucleus and other membrane-bound subcellular structures

euchromatic regions Less densely staining regions of chromosomes that contain active genes.

euchromatin Part of the chromatin that takes up stain less than heterochromatin, contains active genes.

Euglenophyta A group of unicellular protists, usually green or colorless with two flagella per cell.

eukaryote Having a true nucleus; a cell that has membranous organelles, most notably the nucleus.

eukaryotic cell A cell containing a membrane-bounded nucleus and membrane-bounded organelles.Compare prokaryotic cell.

eukaryotic, eucaryotic Organisms whose cells characteristically contain a membrane-bound nucleus or nuclei; contrasts with prokaryotic.

euploidy Change in chromosome number from one generation to the next in which there is an addition or deletion of a complete set of chromosomes in the progeny; the most common type is polyploidy.

euryhaline Able to tolerate wide ranges of saltwater concentrations.

euryphagous Eating a large variety of foods.

eurytopic Refers to an organism with a wide environmental range.

eusocial A social system involving reproductive division of labor (i.e., castes) and cooperative rearing of young by members of previous generations.

eutectic chemicals Phase-changing chemicals used in heat storage systems to store a large amount of energy in a small volume.

eutely Condition where the body is composed of a constant number of cells or nuclei in all adult members of a species (e.g., rotifers, some nematodes, and acanthocephalans).

eutrophic Rivers and lakes rich in organisms and organic material (eu 5 truly; trophic 5 nutritious).

eutrophication Succession in a lake. The gradual accumulation of nutrients and plant and animal growth that eventually transforms a lake into a marsh and then a forest. The death of a lake.

evagination An outpocketing from a hollow structure.

evaporation The escape of molecules from the liquid phase into the gaseous phase, or vapor.

evaporative cooling The lower speed and hence the lower temperature of molecules remaining in the liquid phase after evaporation of the fastest molecules.

evapotranspiration The combined water loss from both leaf surfaces and from the soil surface; the sum of transpiration and evaporation.

evergreens Coniferous trees and broad-leaved plants that retain their leaves year-round.

evisceration The expulsion of internal organs in sea cucumbers.

evolution Change over time. Organic or biological evolution is a series of changes in the genetic composition of a population over time. See also natural selection and punctuated equilibrium model.

evolutionarily stable strategy (ESS) A strategy that when employed by most individuals in a population cannot be outcompeted by some alternative strategy.

evolutionary adaptation The changes occurring in a population of individuals over many generations by processes of natural selection.

evolutionary duration The length of time that a species or higher taxon exists in geological time.

evolutionary species concept A single lineage of ancestral-descendant populations that maintains its identity from other such lineages and has its own evolutionary tendencies and historical fate; differs from the biological species concept by explicitly including a time dimension and including asexual lineages.

evolutionary systematics The study of the classification of, and evolutionary relationships among, animals; evolutionary systematists attempt to reconstruct evolutionary pathways based on resemblances between animals that result from common ancestry.

evolutionary taxonomy A system of classification, formalized by George Gaylord Simpson, that groups species into Linnean higher taxa representing a hierarchy of distinct adaptive zones; such taxa may be monophyletic or paraphyletic but not polyphyletic.

excision repair Means by which cells are able to repair certain kinds of damage (dimerized pyrimidines) in their DNA.

excitation Electron movement caused by light striking the chlorophyll molecule.

exclusive economic zone (EEZ) A zone 200 nautical miles (370 km) wide along the coast where nations have exclusive rights to any resource. It was initiated by the United Nations Convention on the Law of the Sea (UNCLOS).

excretion The act, process, or function of excreting. The elimination of metabolic waste products from an animal's body.

exergonic Characterized or accompanied by the release of energy; said of chemical reactions that release energy, so that the products have a lower free energy than the reactants.

exergonic reaction Chemical reactions that release energy.

exergonic Pertaining to a reaction that gives off energy and occurs spontaneously.

exflagellation Rapid formation of microgametes from a microgametocyte of Plasmodium and related genera.

exhaustible resources Generally considered the earth's geologic endowment: minerals, nonmineral resources, fossil fuels, and other materials present in fixed amounts in the environment.

exine The hard outer coat of a pollen grain.

existence value The importance we place on just knowing that a particular species or a specific organism exists.

exite Lateral process or joint from the protopod, sometimes referred to as an epipod.

exobiology The study of evidence relative to the possibility of life on other planets.

exocarp Outermost layer in the pericarp (fruit wall).

exocrine A type of gland that releases its secretion through a duct; contrasts with endocrine.

exocrine gland A gland that secretes its product to an epithelial surface, directly or through ducts.

exocytosis The process by which substances are moved out of a cell; the substances are transported in the cytoplasmic vesicles, the surrounding membrane of which merges with the plasma membrane in such a way that the substances are dumped outside.

exogenous factors External factors regulating an organism's growth and development.

exon Part of the mRNA as transcribed from the DNA that contains a portion of the information necessary for final gene product.

exopod, exopodite. Lateral branch of a biramous crustacean appendage.

exopterygote Condition of external wing bud development in an insect. Also, any insect in which the wing buds develop externally; associated with hemimetabolous insects.

exopterygote Insect in which the wing buds develop externally during nymphal instars; has hemimetabolous metamorphosis.

exoskeleton A supporting structure secreted by ectoderm or epidermis; external, not enveloped by living tissue, as opposed to endoskeleton.

experience All of the interactions between an organism and its environment, beginning at conception and including both external and internal influences.

experiment An artificially created situation that is used to test a hypothesis. In a controlled experiment, additional variables that might affect the experiment are prevented from doing so.

experimental design The prescription of the treatment groups, dependent and independent variables, and sample sizes for the testing of a particular hypothesis.

experimental hypotheses The biological ideas, both broad and specific, developed from knowledge about previous investigations and our own imagination and creativity, that lead to tests of statistical null hypotheses using experimental designs.

exploitation A type of competition in which organisms passively use up limited resources; also called scramble competition. Contrast with interference or contest competition, in which organisms defend or otherwise control resources.

exploratory behavior The spontaneous search for and active investigation of objects, situations, or other organisms in the absence of any homeostatic need.

exponential growth Growth at a constant rate of increase per unit of time; can be expressed as a constant fraction or exponent. See geometric growth.

extermination The extinction of a species that is caused by humans.

external auditory canal The sound channel connecting the external and middle ears.

external costs Expenses, monetary or otherwise, borne by someone other than the individuals or groups who use a resource.

exteroception Perception of information provided by the exteroceptors.

exteroceptor A sense organ excited by stimuli from the external world.

extinction 1. The irrevocable elimination of species; can be a normal process of the natural world as species out-compete or kill off others or as environmental conditions change. 2. In learning, the decrease of response rate or magnitude of response with lack of reinforcement in a learning situation.

extirpate To destroy totally; extinction caused by direct human action, such as hunting, trapping, etc.

extracellular digestion The digestion that takes place outside cells, usually in a gut, or digestive cavity. Compare intracellular digestion.

extrinsic On the outside; related to some region other than the organ with which it is associated.