8H Science Units and Worksheets

A

Abdomen -- the portion of a tetrapod's body between the thorax and pelvic girdle that contains the visceral organs.

Abductor -- a muscle that performs the action.

Abiotic -- a non-living component of the environment.

Aboral -- the part of the body farthest from the mouth.

Abscess -- dead cells and tissue fluid confined in a localized area, causing swelling.

Absorptive feeding -- a means of taking up dissolved food material through specialized organs or across the body wall.

Acclimation -- the change in tolerance of an animal for a condition in its environment.

Accretion -- an object grown by the process of externally layering material one layer on top of another (pearls).

Acronomic -- describes an animal that dwells in high places (treetops, cliffs, etc.).

Adam's Apple -- the popular name for the thyroid cartilage that is seen in the front of a man's throat.

Adaptation -- an anatomical structure, physiological process, or behavioral trait that evolved by natural selection and improves an organism's ability to survive and leave descendants.

Adenoids -- the pathological enlargement of the lymphoid

Adrenal Glands -- a pair of glands on the kidneys which secrete adrenalin and other hormones.

Adrenaline -- a hormone produced by the adrenal gland.

Aerate -- to supply with oxygen.

Aerial -- pertaining to being in the air, such as a root projecting from an aboveground stem.

Aerobic -- an oxygen-dependent form of respiration.

Afterbirth -- the placental and fetal membranes expelled from the uterus after childbirth.

Aggressive mimicry -- a technique for capturing prey in which the predator uses lures or other means to misinform the prey.

Agnatha -- a superclass of vertebrates whose members lack jaws and paired appendages and possess a cartilaginous skeleton and a persistent notochord. Lampreys and hagfishes.

Alate -- describes an organism with wings.

Alga -- a photosynthetic protist containing plastids. Any of several groups of autotrophs that lack the structural features (true leaves, roots, and stems) of the higher plants.

Alien species (exotic species) -- a species introduced by humans.

Alimentary -- having to do with nutrition or nourishment.

Alimentary canal -- the channel in an animal through which food passes.

Alkaloid -- a group of nitrogen-containing compounds having diverse structures; many alkaloids have medicinal, hallucinogenic, or toxic properties.

Allele -- alternative forms of genes coding for the same trait.

Allergens -- substances that activate the immune system and cause an allergic response; may not be directly antigenic themselves but may make other materials antigenic.

Allopatric -- found in separate and mutually exclusive geographical regions.

Allopatric speciation -- the formation of new species by a process involving geographic barriers.

Alpine -- the high, treeless biome of mountains that consists of grasses algae and/or lichens.

Alternate -- leaf arrangement in which there is only one leaf.

Altricial -- an animal that is helpless at hatching or birth.

Altruism -- the principle or practice of unselfish concern for, or devotion to, the welfare of others.

Alveolus -- a lung air sac where gas exchange with the blood occurs.

Amino acid -- an organic molecule including one or more amino (NH 2 ) and acid (COOH) groups; one of the 20 nitrogen-containing molecules that make up proteins.

Amitosis -- the anatomical term given to cell reproduction by direct division.

Amniocentesis -- a procedure for withdrawing a sample of fluid around the developing embryo for examination of chromosomes in the embryonic cells and other tests.

Amnion -- a membranous sac which surrounds the embryo; it is developed in reptiles, birds and mammals, but not in amphibians or fishes.

Amniotic egg -- the egg of reptiles, birds, and mammals.

Amphibia -- the class of vertebrates whose members are characterized by skin with mucoid secretions, which serves as a respiratory organ. Developmental stages are aquatic and are usually followed by metamorphosis to an amphibious adult. Frogs, toads, and salamanders.

Amplexus -- the positioning of a male amphibian dorsal to female amphibian, his forelimbs around her waist. During amplexus, the male releases sperm as the female releases eggs.

Ampulla (Pl. Ampullae) of Lorenzini -- one of several sensory structures in the head of sharks that detect weak electric fields.

Anabolic -- chemical reactions that synthesize and require energy.

Anadromous -- refers to fishes that migrate up streams from the sea to spawn.

Anaerobic -- not dependent on oxygen for respiration.

Anal fin -- each of the last pair of ventral fins of fishes.

Analgesic -- a pain-relieving remedy.

Anatomy -- the structure and organization of living creatures.

Androgen -- any substance that contributes to masculinization, such as the hormone testosterone.

Androsterone -- an animal hormone not synthesized by plants.

Anemia -- low levels of hemoglobin due to iron deficiency or lack of red blood cells.

Angiosperm -- the group of plants characterized by having flowers as their sexual reproductive structures.

Animalia -- the kingdom of organisms whose members are multicellular, eukaryotic, and heterotrophic. Fish, amphibians, reptiles and mammals are examples.

Ankle -- the joint connecting the foot with the leg.

Annelida -- the phylum of animals whose members are segmented and wormlike. Annelids have a complete digestive tract and a ventral nerve cord.

Annual -- a plant that lives for a single growing season.

Annual ring -- the ring of a tree that corresponds in temperate regions to a chronological year.

Ante -- a prefix meaning before.

Antenna -- a sensory appendage on the head of arthropods, or the second pair of the two such pairs of structures in crustaceans.

Anterior -- the head end of an organism, or (as an adjective) toward that end.

Anther -- the male reproductive organ enclosing and containing the pollen grains.

Anthozoa -- the class of cnidarians whose members are solitary or colonial polyps. Sea anemones and corals.

Antibiotic -- a substance that inhibits the growth of microorganisms.

Antibody -- immunoglobulin protein, produced by B cells (or plasma cells derived from B cells), that binds with a specific antigen.

Anticoagulant -- a substance that prevents blood clotting.

Antigen -- a foreign substance to which lymphocytes respond; also known as an immunogen because it induces the immune response.

Aorta -- the largest artery in the human body. It carries blood from the heart to the arms, legs and head.

Apex predator -- the consumer at the end of a food chain or web; a carnivore that ordinarily has no predator under normal conditions.

Aquaculture -- the farming of marine and freshwater organisms.

Arachnida -- the class of arthropods whose members are mostly terrestrial, possess book lungs, or tracheae, and usually have four pairs of walking legs as adults. Spiders, scorpions, ticks, mites, and harvestmen.

Arbor -- a Latin word meaning tree.

Arboreal -- a term describing an organism living in trees.

Archaea -- the early prokaryotes, differing from bacteria in having unusual types of metabolism, membrane lipids, and amino acid and DNA and RNA base sequences. Today these organisms inhabit extreme environments.

Archosauria ("ruling lizards") -- the Crocodylia, Pterosauria, Dinosauria, and several other closely related groups of animals.

Artery -- the vessel that carries blood away from the heart.

Arthropoda -- the phylum of animals whose members possess a jointed exoskeleton and a ventral nervous system. Insects, crustaceans, spiders, and related animals.

Artiodactyl -- one of an order of mammals with two or four digits on each foot.

Asexual -- lacking sexual reproduction.

Asthma -- a distressing disease characterized by shortness of breath, wheezing, and bronchial muscle spasms.

Asymmetry -- without a balanced arrangement of similar parts on either side of a point or axis.

Atherosclerosis -- a disease characterized by fatty plaques forming in the inner lining of arteries.

Athlete's Foot -- a disease caused by fungi that flourish under warm, wet conditions.

Atrium -- one of the chambers of the heart; also, the tympanic cavity of the ear.

Auricle -- (1) reservoirs within the heart which receive blood from the veins, (2) the portion of the external ear not connected within the head.

Autoimmunity -- an immune response to ones' own proteins or other antigens.

Autonomy -- the self amputation of an appendage. For example, the casting off of a section of a lizard's tail caught in the grasp of a predator. The autotomized appendage is usually regenerated.

Autotroph -- an organism that makes its organic nutrients from inorganic raw materials by using an external energy source, such as light energy. Plants.

Autotrophic -- having the ability to synthesize food from inorganic compounds.

Aves -- a class of vertebrates whose members are characterized by scales modified into feathers for flight, endothermy, and amniotic eggs. The birds.

Axial skeleton -- the portion of the skeleton that supports and protects the organs of the head, neck, and trunk.

Axis -- the 2nd cervical vertebrae. It provides the pivot for the atlas and the head.

B

Bacillus -- a rod-shaped bacterium.

Bacteria -- the prokaryotic and unicellular microorganisms included in the kingdom Monera.

Baleen -- the filtering plates that hang from the upper jaws of baleen whales.

Baleen whales -- the filter-feeding whales.

Bark -- those portions of a woody plant stem or trunk exterior to the vascular cambium.

Barnacles -- crustaceans that live attached to surfaces and are typically enclosed by heavy calcareous plates.

Batesian mimicry -- evolution by one species to resemble the coloration, body shape, or behavior of a related species that is protected from predators by a venomous stinger, bad taste, or some other adaptation.

Benthic -- pertaining to the bottom region of an ocean, lake, or pond.

Berry -- a fleshy, two- or multiple-carpeled ovary, each carpel having many seeds.

Beta-carotene -- the yellow to red pigment in plants that converts to vitamin A in animals.

Biceps -- a long fusiform muscle on the front of the arm used to flex the elbows.

Bicuspid -- either of the two double-pointed teeth that in humans are situated between the canines and the molars on each side of each jaw.

Biennial -- a plant that completes its life cycle within two growing seasons. A carrot.

Bilateral symmetry -- an animal body plan with mirror image left and right sides.

Bile -- a fat emulsifying fluid secreted by the liver, stored in the gall bladder and poured into the small intestine via the bile duct.

Bimodal breathing -- the ability of an organism to exchange respiratory gases simultaneously with both air and water; usually using gills for water breathing and lungs for air breathing.

Binary fission -- asexual reproduction in protists in which mitosis is followed by cytoplasmic division, producing two new organisms.

Binomial -- the two names, genus and species, comprising the scientific name.

Binomial nomenclature -- a system of naming species using two names, the first of which refers to the genus.

Biocentrism -- the belief that all creatures have rights and values; being centered on nature rather than humans.

Biochemistry -- the chemistry of living organisms and of vital processes.

Biocide -- a broad-spectrum poison that kills a wide range of organisms.

Biodegradable -- a chemical that can be broken down by bacteria or other organisms.

Biodiversity -- the genetic, species, and ecological diversity of the organisms in a given area.

Biogeography -- the study of the distribution of life on earth.

Biological clock -- an internal timing mechanism that involves both an internal self-sustaining pacemaker and cyclic environmental synchronizers.

Biology -- the study of all living organisms.

Bioluminescence -- a method of light production by living organisms in which usually certain proteins, oxygen and enzymes are present.

Biomass -- the weight of total living organisms or of a species population per unit of area.

Biomes -- distinctive associations of plant and animal populations; characterized by certain geographical boundaries and specific climatic and geographical features.

Biosphere -- Earth and all of its ecological interactions considered as a single system.

Biotechnology -- the use of living organisms to provide products for humanity; using genetic engineering to create organisms with useful traits.

Biotic factor -- the living components in the environment.

Bipeds -- animals that walk upright on two legs.

Birds (class aves) -- vertebrates that have feathers and lay eggs with calcified shells on land.

Bivalves (class bivalvia) -- the clams, mussels, and other molluscs that possess a two-valved shell, filtering gills, and a shovel-like foot.

Bivalvia -- the class of molluscs whose members are enclosed in a shell consisting of two dorsally hinged valves, lack a radula, and possess a wedge-shaped foot. Clams, mussels, oysters.

Black lung disease -- inflammation and fibrosis caused by accumulation of coal dust in the lungs or airways.

Black smoker -- a chimney-like accumulation of mineral deposits that is found at hydrothermal vents.

Bladder -- a sack in the abdomen that collects urine produced by the kidneys.

Blade -- the flat, green part of a leaf or the expanded or flattened portion of a brown alga.

Blood -- a body fluid that carries food and oxygen to the cells.

Blood plasma -- the liquid, noncellular fraction of blood, including dissolved substances.

Blood pressure -- the force with which blood is pushed against the walls of blood vessels and circulated throughout the body when the heart contracts.

Blood type -- a genetically determined characteristic of human blood; the common blood types are designated a, b, o, ab, rh negative and rh positive.

Bloom -- a dense concentration of phytoplankton that occurs in response to optimum growth conditions.

Blowhole -- the nostrils, or nasal openings, of cetaceans.

Blubber -- the fat found between the skin and muscle of whales and other cetaceans, from which oil is made.

Blue-green algae -- prokaryote organisms with photosynthetic pigments.

B-lymphocytes -- the cells that manufacture antibodies involved in immunity.

Bog -- an area of waterlogged soil that tends to be peaty; fed mainly by precipitation; low productivity; some bogs are acidic.

Bone -- the hard skeletal part of an animal that provides protection and support.

Bony fishes -- fishes with a skeleton made mostly of bone; they also have gill covers.

Boreal -- relating to a northern biotic area characterized by a predominance of coniferous forests and tundra.

Boreal forest -- a broad band of mixed coniferous and deciduous trees that stretches across northern North America (and also Europe and Asia ); its northernmost edge, the taiga, intergrades with the arctic tundra.

Botany -- the study of plants.

Bowels -- the division of the alimentary canal below the stomach.

Brachiopoda -- a phylum of marine animals whose members possess a bivalved calcareous and/or chitinous shell that is secreted by a mantle and encloses nearly all of the body. Unlike the molluscs, the valves are dorsal and ventral. Lampshells.

Brain -- the central organ of the nervous system.

Branchial -- referring to gills.

Breaching -- the process of leaping into the air by whales.

Broadcast spawners -- marine animals that reproduce by releasing eggs and sperm into the water.

Bronchi -- the paired ventilatory tubes of a vertebrate that branch into each lung at the lower end of the trachea.

Bronchitis -- an inflammation of bronchial linings that causes persistent cough, copious production of sputum, and involuntary muscle spasms that constrict airways.

Brood patch -- the patch of feathers used by birds to incubate eggs.

Brooding -- the parental care of developing young.

Brown algae -- seaweeds with a predominance of yellow and brown pigments.

Budding -- a form of asexual reproduction in which new individuals develop from a portion of the parent.

By-catch -- the less valuable catch that is captured while fishing for a more valuable catch.

C

Calcium carbonate -- a mineral that is the major component of the shell, skeleton, and other parts of many organisms.

Calorie -- the amount of heat energy required to raise the temperature of 1g of water 1 degree C.

Cambrian -- a geological period of the Paleozoic beginning about 590 million years ago and lasting about 85 million years, during which time many divisions of protists occurred in the oceans.

Campestral -- a characteristic of rural locations, especially open country and grasslands.

Cancer -- invasive, out-of-control cell growth that results in malignant tumors.

Canine -- relating to, affecting, resembling or derived from a dog .

Canopy -- the upper portion of a population of plants; the term is usually associated with forests and agricultural crops.

Capillary -- a fine blood vessel which carries blood to cells.

Captive breeding -- raising plants or animals in zoos or other controlled conditions to produce stock for subsequent release into the wild.

Carbohydrate -- compounds of carbon, hydrogen, and oxygen that provide a structural component of living cells and a source of energy for animals in the form of sugars.

Carbon -- an element that is an essential constituent of all organic compounds.

Carbon dating -- a procedure used to determine the age of fossils.

Carbon dioxide -- a colorless gas that is required in the process of photosynthesis.

Carbonic acid -- atmospheric co 2 dissolved in water to yield h 2 co 3 , a weak acid.

Carboniferous -- a geological period of the Paleozoic beginning approximately 360 million years ago and lasting about 85 million years. During this time forests appeared and became dominant, composed of arborescent club mosses, horsetails, and ferns. Their extinction resulted in the formation of coal deposits.

Carcinogens -- substances that cause cancer.

Cardiac -- belonging or relating to the heart.

Carnivore -- any organism that eats animals.

Carpal -- the wrist.

Carrying capacity -- the maximum number of a population that can be supported by the environment over a given period of time.

Cartilage -- a spongy tissue that covers the ends of the bones where they come together making a joint.

Cartilaginous fishes (class Chondrichthyes) -- fishes with a skeleton made of cartilage: sharks, rays, skates, and ratfishes (or chimaeras).

Cash crops -- crops that are sold rather than consumed or bartered.

Caste -- one of the polymorphic forms within an insect society, each caste having its specific duties, as queen, worker, soldier, and so on.

Catabolic -- chemical reactions that release energy by degrading complex compounds into simpler ones.

Catadromous -- refers to fishes that migrate from fresh water to the ocean to spawn.

Caudal -- constituting, belonging to, or relating to a tail.

Caudal (posterior) -- toward the south wall or butt.

Cell -- minute biological compartments within which the processes of life are carried out.

Cellular respiration -- the process in which a cell breaks down sugar or other organic compounds to release energy used for cellular work; may be anaerobic or aerobic, depending on the availability of oxygen.

Cellulose -- the chief polysaccharide constituent of the cell wall of green plants and some fungi; an insoluble carbohydrate that is converted into glucose.

Cenozoic -- a geological era beginning 65 million years ago and extending to the present, characterized by major adaptive radiation of specialized life forms and formation of biomes.

Central vacuole -- a membrane-enclosed sac that takes up most of the volume of a mature plant cell.

Cephalaspidomorphi -- the class of vertebrates characterized by the absence of paired appendages and the presence of sucking mouthparts with teeth and a rasping tongue. Lampreys.

Cephalochordata -- the subphylum of chordates whose members possess a laterally compressed, transparent body. They are fishlike and possess all four chordate characteristics throughout life. Amphioxus.

Cephalopods (class Cephalopoda) -- octopuses, squids, and other molluscs that possess a foot modified into arms that surround the head.

Cephalothorax -- a body division found in many Arachnida and higher crustacea, in which the head is fused with some or all of the thoracic segments.

Cereals -- members of the grass family that yield a large amount of grain rich in carbohydrates, fats, proteins, and vitamins.

Cerebellum -- the lower part of the brain that coordinates and control skeletal muscle movement.

Cerebrum -- the largest part of the mammalian brain that occupies the dome of the cranium.

Cervical -- relating to a neck.

Cervical vertebrae -- the seven vertebrae closest to the skull.

Cestoidea -- the class of platyhelminthes that has members that are all parasitic with no digestive tract; have great reproductive potentials. Tapeworms.

Cetaceans (order Cetacea) -- marine mammals with anterior flippers, no posterior limbs, and a dorsal fin. Whales, dolphins, and porpoises.

Chaparral -- a relatively dry biome that occurs in the southwestern United States .

Character -- any well-defined feature, whether anatomical, behavioral, biochemical, or genomic, of an organism.

Chelicerata -- the subphylum of arthropods whose members have a body that is divided into prosoma and opisthoma. The first pair of appendages are feeding appendages called chelicerae. Spiders, scorpions, mites, and ticks.

Chemoreceptor -- a receptor that is stimulated by the presence of certain chemical substances.

Chemosynthesis -- autotrophic synthesis of organic compounds by certain bacteria; uses energy from inorganic compounds.

Chemotroph -- an organism that derives nourishment from inorganic substances without using chlorophyll.

Chigger -- a parasitic mite of the family Trombiculidae.

Chinampas -- long, narrow strips of land bordered on three sides by irrigation canals which can produce several crops per year.

Chlorofluorocarbons (cfcs) -- chemicals used in sprays and other products that affect the ozone layer.

Chlorophyll -- the green pigment found in plants and in some animals; necessary for photosynthesis.

Chloroplast -- a plastid containing chlorophyll and usually other pigments, found in cytoplasm of plant cells.

Cholesterol -- a steroid that is an integral part of cell membranes and a precursor to other steroidal compounds in animals.

Chondrichthyes -- the class of vertebrates whose members are fishlike, possess paired appendages and a cartilaginous skeleton, and lack a swim bladder. Skates, rays, and sharks.

Chordata -- a phylum of animals whose members are characterized by a notochord, pharyngeal gill slits, a dorsal tubular nerve cord, and a postanal tail.

Chromoplast -- membrane-bound organelle containing pigments other than chlorophyll; the pigments may be yellow, orange, or red.

Chromosome -- a rod-like structure that appears in the nucleus of a cell during mitosis; contains the genes responsible for heredity.

Chrysalis -- the pupal case of a butterfly that forms from the exoskeleton of the larva.

Ciguatera -- a type of poisoning found in tropical fishes. It may result from a toxin produced by a dinoflagellate.

Cilium (pl. Cilia) --a short, hair-like flagellum that is found in large numbers and used in movement, for pushing food particles, and in other functions.

Circadian -- occurring at a period of approximately 24 hours.

Circadian rhythms -- daily cycles of activity.

Circulatory system -- pertaining to the circulation. Also cardiovascular system.

City -- a differentiated community with a sufficient population and resource base to allow residents to specialize in arts, crafts, services, and professional occupations.

Clade -- a taxon or other group consisting of an ancestral species and all of its descendants, forming a distinct branch on a phylogenetic tree.

Cladistics -- a system of arranging taxa by analysis of evolutionarily derived characteristics so that the arrangement will reflect phylogenetic relationships.

Clasper -- a copulatory organ along the inner edge of each pelvic fin in male sharks and other cartilaginous fishes.

Class -- taxonomic rank consisting of related orders.

Clavicle (collarbone) -- a long bone which lies almost horizontally at the root of the neck.

Claw -- the sharp, usually curved, nail on the foot of an animal or insect. The pincer-like extremity of specific limbs of certain arthropods (e.g., lobster claws).

Clear-cut -- cutting every tree in a given area, regardless of species or size; an appropriate harvest method for some species; can be destructive if not carefully controlled.

Climate -- a description of the long-term pattern of weather in a particular area.

Climatology -- the study of climates and the factors influencing them.

Cloaca -- the posterior chamber of digestive tract in many vertebrates, receiving feces and urogenital products. In certain invertebrates, a terminal portion of digestive tract that serves also as respiratory, excretory, or reproductive tract.

Clone -- a series of identical cells or individuals that have developed from a single cell or individual.

Closed canopy -- a forest where tree crowns spread over 20 percent of the ground.

Cloud forests -- high mountain forests where temperatures are uniformly cool and fog or mist keeps vegetation wet all the time.

Cnidaria -- the phylum of animals whose members are characterized by radial or biradial symmetry, diploblastic organization, a gastrovascular cavity, and nematocysts. Jellyfish, sea anemones, and their relatives.

Coagulation -- a process in which a series of enzymes are activated, resulting in clotting of blood.

Coal washing -- coal technology that involves crushing coal and washing out soluble sulfur compounds with water or other solvents.

Coccus -- any of various spherical-shaped bacteria.

Coccyx (tailbone) -- the bone at the apex of the sacrum of anthropoids. It is usually comprised of 4 vertebrae fused together.

Cochlea -- a tubular cavity of the inner ear containing the essential organs of hearing; occurs in crocodiles, birds, and mammals; spirally coiled in mammals.

Cocoon -- a protective covering of a resting or developmental stage, sometimes used to refer to both the covering and its contents; for example, the cocoon of a moth or the protective covering for the developing embryos in some annelids.

Coelacanths -- a group of lobed-fin fossil fishes. Latimeria was discovered alive in 1952.

Coenose -- an assemblage of fossils.

Cognition -- the processes in the minds of animals or their general mental functions, including perception, representation, and memory.

Colon -- the large intestine.

Colonization -- the pioneer establishment of vegetation on a previously unvegetated area.

Commensalism -- a relationship in which one individual lives close to or on another and benefits, and the host is unaffected.

Common ancestor -- the hypothetical single species of organisms that two or more different species of organisms evolved from.

Communal nesting -- more than one female in a nest raising the young of more than one female.

Communication -- an act on the part of one organism (or cell) that alters the probability of patterns of behavior in another organism (or cell) in an adaptive fashion.

Community -- the combined populations of organisms in a given area.

Comparative anatomy -- the study of animal structure in an attempt to deduce evolutionary pathways in particular animal groups.

Competition -- an overlap of ecological niches where two populations in the same community depend on the same food source, shelter, or other resources.

Compost -- partially decayed organic matter used in gardening and farming to enrich the soil and increase water holding capacity.

Composting -- the biological degradation of organic material under aerobic (oxygen-rich) conditions to produce compost, a nutrient-rich soil amendment and conditioner.

Compound eye -- an eye consisting of many individual lens systems. Present in many members of the phylum Arthropoda.

Compound fruit -- a fruit consisting of several individual fruits held together (pineapple) or in which separate carpels of a flower stay together (blackberry).

Compound leaf -- a leaf composed of two or more completely independent blade units called leaflets.

Compression -- a fossil formed when carbonized plant material is still present in the original shape but is greatly compressed and reduced in size by pressure.

Conditioning -- a form of learning in which a behavior is associated with a reward such as food.

Coniferous forest -- a community type dominated by cone-bearing gymnosperms mostly in the northern hemisphere.

Conifers -- needle-bearing trees that produce seeds in cones.

Connective tissue -- a basic type of tissue that includes bone, cartilage, and various fibrous tissues.

Conservation -- to protect, conserve the natural world and all its components.

Consumer -- a heterotroph.

Contagious -- capable of being transmitted through direct contact.

Continuous feeder -- usually slow-moving sessile animals that feed all of the time.

Contour feathers -- feathers that cover the body, wings, and tail of a bird. Contour feathers provide flight surfaces and are responsible for plumage colors.

Contour plowing -- plowing along hill contours to reduce erosion.

Control group -- an observed, unmanipulated set of test subjects.

Control -- that part of a scientific experiment to which the experimental variable is not applied but which is similar to the experimental group in all other respects.

Convergent -- describes characters that are similar in structure and function but have arisen separately rather than from a common ancestor. Convergence is common in groups that become adapted to a similar habitat or way of life; the similar body shapes of the North American gray wolf and the Tasmanian wolf, each evolving from different ancestors (the former is a placental mammal, the latter is a marsupial mammal), resulted from secondary adaptation to similar habitats.

Cool deserts -- deserts such as the American great basin characterized by cold winters and sagebrush.

Cooperative breeding -- a breeding system in which non-parents share in rearing the young.

Copepods -- small, mostly planktonic crustaceans.

Coprolite -- fossilized fecal material.

Copulation -- sexual union to facilitate the reception of sperm by the female.

Coral reefs -- prominent oceanic features composed of hard, limy skeletons produced by coral animals.

Core area -- the area of heaviest use within the home range.

Coriolis Effect -- the apparent change in direction of a moving object (to the left in the southern hemisphere and to the right in the northern hemisphere) due to the rotation of the earth.

Cornea -- the outer transparent coat of the eye.

Corolla -- the collective term for the petals of a flower.

Corona -- a crown or encircling structure.

Coronary -- encircling as a crown. 1. Vessels encircling the heart. 2. A condition caused by a decreased blood flow to the heart muscle.

Corridor -- a strip of natural habitat that connects two adjacent nature preserves to allow migration of organisms from one place to another.

Cortisone -- an animal hormone not synthesized by plants.

Cosmopolitan -- worldwide in distribution.

Costal cartilages -- bars of hyaline cartilage which extend forwards from the anterior ends of the ribs and contribute to the elasticity of the thorax.

Cotyledon -- a seed leaf; the first leaf formed in a seed.

Counterillumination -- the emission of light by mid-water animals to match the background light.

Countershading -- contrasting coloration that helps conceal the animal (e.g., the darkly pigmented top and lightly pigmented bottom of frogs).

Coursers -- predators that chase their prey over long distances.

Courtship behavior -- a behavior related to the attraction of the opposite sex and mating.

Cover crops -- plants, such as rye, alfalfa, or clover that can be planted immediately after harvest to hold and protect the soil.

Cranial, or anterior -- toward the north wall or head.

Crepuscular -- daily cycles with peak activity around dusk and/or dawn.

Crinoidea -- the class of echinoderms whose members are attached by a stalk of ossicles or are free living. Sea lilies and feather stars.

Croplands -- lands used to grow crops.

Cross-pollination -- the transfer of pollen from the stamen to the stigma of a flower of another plant.

Crown -- the topmost portion of a plant.

Crustacea -- the subphylum of mandibulate arthropods whose members are characterized by having two pairs of antennae, one pair of mandibles, two pairs of maxillae, and biramous appendages. Crabs, crayfish, lobsters.

Cursorial -- describes an animal built for rapid terrestrial locomotion.

Cuticle -- a protective layer secreted by the hypodermis of many invertebrates, the outside layer of skinin higher animals, or the waterproof layer of cutin on leaves and non-woody stems.

Cycads -- members of the Cycadophyta, which have unbranched stems and a terminal grouping of leathery, compound leaves.

Cycle -- repeating units that make up the pattern of biological rhythms.

Cyst -- a secreted covering that protects many small invertebrates, including some protozoans, rotifers, and nematodes, from environmental stresses, such as desiccation and overcrowding. In diatoms, a resistant and photosynthetically inactive cell.

D

Dactylozooid -- a polyp of a colonial hydroid specialized for defense or killing food.

Decapods -- crustaceans with five pairs of walking legs and a well-developed carapace. The group includes the shrimps, lobsters, hermit crabs, and crabs.

Deciduous -- referring to plants that lose all their leaves during the cool season.

Deciduous forest -- a forest biome in which the dominant trees are deciduous.

Decomposer -- bacteria and fungi that obtain organic nutrients by breaking down the remains or products of other organic compounds.

Decongestant -- an agent that relieves nasal or respiratory congestion.

Delta -- a fan-shaped sediment deposit found at the mouth of a river.

Deltoid -- a triangular muscle in the shoulder used to lift the upper arm.

Demand -- the amount of a product that consumers are willing and able to buy at various possible prices.

Demersal fish -- a bottom-dwelling fish.

Demography -- the vital statistics about people: births, marriages, deaths, etc.; the statistical study of human populations relating to growth rate, age structure, geographic distribution, etc., and their effects on social, economic, and environmental conditions.

Dendrochronology -- the science of studying growth rings of trees to determine past conditions.

Dendroclimatology -- the s tudy of the annual rings of trees in order to interpret climatic changes in the past.

Dengue -- a virus or disease transmitted by mosquitoes.

Denticles -- small, tooth-like projections.

Dependent variable -- what may change (e.g., aggression) in response to manipulation of an independent variable (e.g., food supply) by the experimenter.

Depressant -- a psychoactive drug that has a sedative effect on the central nervous system.

Derived -- describes a character or group of characters that has changed from its primitive state; advanced.

Dermal -- pertaining to the skin.

Dermal tissue -- the tissue that covers surfaces in plants.

Dermatitis -- an infection or inflammation of the skin.

Dermatophytes -- certain imperfect fungi that cause skin diseases in humans; includes the organisms causing ringworm and athlete's foot.

Dermis -- the layer of the skin deep to the epidermis, consisting of a dense bed of vascular connective tissue.

Desalinization (desalination) -- the removal of salt from water by distillation, freezing, or ultrafiltration.

Descendant -- describes a species or taxon that has evolved from another species or from within a taxon.

Desert -- a type of biome characterized by low moisture levels (below 25 cm per year), and infrequent and unpredictable precipitation.

Desertification -- a process by which semiarid ecosystems lose productivity because of loss of plant cover, soil erosion, salinization, or waterlogging.

Despot -- a dominant individual that controls resources.

Detritivore -- organisms that consume organic litter, debris, and dung.

Detritus -- dead organic matter and the decomposers that live on it.

Devonian -- a geological period of the Paleozoic era beginning about 400 million years ago. During this period major diversification of the early land plants occurred.

Diabetes -- a condition characterized by a high blood glucose level and the appearance of glucose in the urine due to a deficiency of insulin or the inability of body cells to respond to insulin.

Diaphragm -- a large transvers muscle at the base of the thorax used in respiration to draw air into the lungs of mammals.

Diastolic pressure -- the blood pressure measurement during the interval between heartbeats; it is the second number shown in a blood pressure reading.

Diatoms -- unicellular and eukaryotic autotrophs; mostly planktonic.

Dichotomous -- pertaining to the division or forking of a single axis into two branches.

Dicotyledon (dicot) -- a class of angiosperms in which the seedlings typically possess two cotyledons.

Dieback -- a sudden population decline; also called a population crash.

Digestion -- the process by which larger molecules of food substances are broken down into smaller molecules that can be taken up by the digestive system.

Dimorphic -- having more than one form, size, or appearance; usually referring to the difference between males and females of a species.

Dimorphism -- the existence within a species of two distinct forms according to color, sex, size, organ structure, and so on.

Dinoflagellates -- unicellular, eukaryotic, mostly autotrophic organisms with two unequal flagella.

Dinosauria ("fearfully great lizards") -- animals, partly distinguished by a largely to fully open acetabulum, that first evolved in the latter third of the Triassic and was the dominant land animal from the early Jurassic to the end of the cretaceous.

Diplopoda -- the class of arthropods whose members are characterized by having two pairs of legs per apparent segment and a body that is round in cross section. Millipedes.

Discontinuous feeder -- an animal that does not feed all the time; instead it generally eats large meals sporadically and does not spend time in the continuous pursuit of prey.

Disease -- a deleterious change in the body's condition in response to destabilizing factors, such as nutrition, chemicals, or biological agents.

Dispersal -- a more or less permanent movement of an individual from an area, such as movement of a juvenile away from its place of birth.

Display -- any behavior pattern especially adapted in physical form or frequency to function as a social signal in communication.

Distal -- away from the body.

Diurnal -- an animal with an activity period during the light portion of the daily cycle.

Diurnal tide -- a tidal pattern with a high and a low tide each day.

Diversity -- the number of species present in a community, as well as the relative abundance of each species.

Diving reflex -- the reflex certain animals have to stay underwater for prolonged periods of time.

Division -- a taxonomic rank that includes related classes.

DNA (deoxyribonucleic acid) -- the long, double-helix molecule in the nucleus of cells that contains the genetic code and directs the development and functioning of all cells.

Dominance hierarchy -- a social ranking, formed through agonistic behavior, in which individuals are associated with each other so that some have greater access to resources than do others.

Dominant -- (1) the most prevalent species in a plant community. (2) the allele that has its trait expressed. (3) a gene that has its phenotypic expression appear in the offspring, regardless of the nature of its allelic partner.

Dormant -- having reduced metabolic and respiratory activity.

Dorsal -- the back of an animal; usually the upper surface; synonymous with posterior for animals that walk upright.

Down feathers -- the insulating f eathers of adult and immature birds.

Down syndrome -- a congenital syndrome including mental retardation, caused by the cells in a person's body having an extra chromosome 21; also called trisomy 21.

Drift net -- a very long fishing net that is allowed to drift for a long time before it is pulled on board.

Drip irrigation -- a method of irrigation that u ses pipe or tubing perforated with very small holes to deliver water one drop at a time directly to the soil around each plant.

Drives -- the specific motivations corresponding to specific needs.

Drought -- an environmental condition in which precipitation is not sufficient to maximize biological productivity.

Duodenum -- the first and shortest portion of the small intestine lying between the pyloric end of the stomach and the jejunum.

Dura Mater -- the membrane that covers the brain.

E

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.

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.

Ecological development -- a gradual process of environmental modification by organisms.

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 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 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.

Ecotourism -- a combination of adventure travel, cultural exploration, and nature appreciation in wild settings.

Ectoparasite -- parasite that lives on the outer surface of its host.

Ectopic -- an 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.

Ectotherm -- an organism whose internal temperature varies with that of the environment; cold-blooded.

Edema -- the 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.

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.

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

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 Nino 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 Nino is a warming of the surface currents in the eastern pacific, only one of the many consequences of ENSO.

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

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

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.

Elephantiasis -- a disfiguring condition caused by chronic infection with filarial worms W uchereria bancrofti and B rugia malayi .

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.

Emergent plant community -- a marine plant community in which most leafy growth occurs above sea level.

Emigrate -- to move from one area to another to take up residence.

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.

Encephalitis -- an infection of the brain, especially by viruses or amoebas.

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 -- native to a certain region or country.

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.

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

Endoparasite -- a 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.

Endotherm -- an organism that can regulate its internal temperature; warm-blooded.

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

Enteron -- the digestive cavity.

Entomology -- the study of insects.

Entozoic -- living within another animal; internally parasitic.

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 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 resistance -- all of 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 and 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.

Enzymes -- molecules, usually proteins or nucleic acids, which act as catalysts in biochemical reactions.

Epi -- a prefix meaning on, upon, or over.

Epidemic -- a sharp rise in the incidence of an infection or disease.

Epidemiology -- the study of the distribution and causes of disease and injuries in human populations.

Epidermis -- the outer, nonvascular layer of skin.

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

Epizootic -- a massive infection rate among animals other than humans; identical to an epidemic in humans.

Equatorial currents -- major ocean currents that move parallel to the equator.

Erythrocyte -- a 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.

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

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

Estrogen -- the female sex hormone in vertebrates.

Estrous -- the period of highest sexual receptivity (or "heat") in some female mammals that coincides with the time of egg release by the ovary marked 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 -- an alcohol made through the process of fermentation of grain.

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.

Eukaryote -- having a true nucleus.

Eutrophication -- the process of 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.

Evergreens -- a coniferous trees and broad-leaved plants that retain their leaves year-round.

Evolution -- change over time. Organic or biological evolution is a series of changes in the genetic composition of a population over time.

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 taxonomy -- a system of classification, formalized by George Gaylord Simpson, that groups species into Linnaean higher taxa representing a hierarchy of distinct adaptive zones.

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

Exhaustible resources -- minerals, non-mineral resources, fossil fuels, and other materials present in fixed amounts in the environment.

Exocrine gland -- one which secretes onto a surface, like a sweat gland.

Exoskeleton -- an external skeleton. Lobster, crawfish, spider.

Exploitation -- a type of competition in which organisms passively use up limited resources.

Exponential growth -- growth at a constant rate of increase per unit of time; can be expressed as a constant fraction or exponent.

Extermination -- the extinction of a species that is caused by humans.

Extinction -- the 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.

Extirpate -- to destroy totally; extinction caused by direct human action, such as hunting, trapping, etc.

Extrinsic -- on the outside; related to some region other than the organ with which it is associated.

F

Facial -- pertaining to the face.

Faculative biped -- describes an animal that walks or otherwise moves about on its two hind limbs, but can and does spend some time locomoting on all four limbs.

Faculative quadruped -- describes an animal that walks or otherwise moves about on all four limbs, but can and does spend some time locomoting on only its hind limbs.

Family -- the level of classification between order and genus.

Family planning -- planning the timing of birth and having as many babies as are wanted and can be supported.

Famines -- acute food shortages characterized by large-scale loss of life, social disruption, and economic chaos.

Fat -- a triglyceride that is solid at room temperature and usually of animal origin.

Fatigue -- the loss of efficiency in the performance of a motor act when that act is repeated in rapid succession.

Fatty acid -- any of a series of saturated organic acids that occur in natural fats of animals and plants.

Fauna -- all of the animals present in a given region.

Female defense polygyny -- males controlling access to females directly by competing with other males.

Femur -- the upper leg bone (thigh), which is the longest and strongest bone in the skeleton.

Fen -- an area of waterlogged soil that tends to be peaty; fed mainly by upwelling water.

Feral -- domestic animal that has taken up a wild existence.

Fertile Crescent -- area between the Tigris and Euphrates Rivers in the Near East ; some of the earliest documented sites of agriculture.

Fertility -- a measurement of the actual number of offspring produced through sexual reproduction.

Fertilization -- the union of gametes. It can be external and take place in the water, or internal and take place within the body.

Fetch -- the span of the sea surface over which the wind blows to form wind-driven waves.

Fetus -- from the seventh or eighth week of gestation.

Fibrosis -- the general name for accumulation of scar tissue in the lung.

Fibula -- the slender lower leg bone.

Filament -- the part of the stamen in a flower that supports the anther.

Filter feeder -- an organism that filters food particles from the surrounding fluid.

Fin ray -- each of the bony spines in the fins of bony fishes.

Finite resources -- resources that have a limit to their availability.

Finlet -- small median fin on the dorsal and ventral sides of the rear parts of tuna and similar fish.

Fire ecology -- the study of the environmental effects of fire.

First World -- the industrialized capitalist or market-economy countries of Western Europe, North America, Japan, Australia, and New Zealand.

Fish meal -- a fish-protein supplement used in animal feeds.

Fission -- asexual reproduction in which the cell divides into two (binary fission) or more (multiple fission) daughter parts, each of which becomes an individual organism.

Fitness -- the degree of adjustment and suitability for a particular environment. Genetic fitness is relative contribution of one genetically distinct organism to the next generation; organisms with high genetic fitness are naturally selected and become prevalent in a population.

Fjord -- a deep coastal water filled valley caused by glacial erosion.

Flagella -- elongated appendages of certain cells used in locomotion.

Flagging behavior -- alarm signaling, as with the use of the tail.

Flatworms (phylum Platyhelminthes) -- invertebrates that are flattened and have an incomplete digestive tract, true organs, and organ systems.

Flexion -- decreasing a joint’s angle.

Flood -- an overflow of water onto land that normally is dry.

Floodplains -- low lands along riverbanks, lakes, and coastlines subjected to periodic flooding.

Flora -- all of the plants present in a given region.

Flower -- the reproductive structure of the Anthophyta or angiosperms.

Flowering plants (angiosperms; division Anthophyta) -- plants that have flowers, seeds, and true leaves, stems, and roots.

Fluke -- a parasitic flatworm of class Trematoda or class Monogenea.

Fluorescence -- longer wavelength emissions which can result form excited electron energy, results in a glowing light.

Flushing time -- the time required for all of the water of an estuary to be completely exchanged.

Follicle -- a single, dry fruit that splits along one seam; example: milkweed.

Food chain -- a sequence of organisms in which plants are the primary food source for herbivores, which are in turn the food source for carnivores, etc., until the top carnivore level is reached.

Food vacuole -- an organelle in the cell that functions in intracellular digestion.

Food web -- a community food chain depicting which species feed on each other and how many interrelationships are involved.

Forager -- a hunter-gatherer group.

Foraging behavior -- the process animal’s use in locating food resources.

Forest management -- scientific planning and administration of forest resources for sustainable harvest, multiple use, regeneration, and maintenance of a healthy biological community.

Fossil -- any evidence of pre-existing life which is preserved in rock.

Fossil fuels -- organic molecules derived from partially decayed plant and animal matter, produced primarily during the Carboniferous period; includes oil, gas, and coal.

Fossorial -- characterized by digging or burrowing.

Fouling organisms -- organisms that live attached to submerged surfaces such as boats and pilings.

Fourth World -- a political/economic category describing very poor nations that have neither market economies nor central planning and are either not developing or are developing very slowly. Also used to describe indigenous communities within wealthier nations.

Fresh water -- water other than seawater.

Freshwater ecosystems -- ecosystems in which the fresh (nonsalty) water of streams, rivers, ponds, or lakes plays a defining role.

Frond -- the photosynthetic leaf blade of a fern.

Frontier -- an unexploited natural area at the leading edge of human settlement.

Fructose -- often referred to as fruit sugar.

Fruit -- a mature ovary.

Fundamental niche -- the multidimensional space that an animal would occupy under optimal conditions in the absence of competitors.

Fungi -- one of the five kingdom classifications; consists of non-photosynthetic, eukaryotic organisms with cell walls, filamentous bodies, and absorptive nutrition.

Fungicide -- chemical that kills fungi.

G

Gaia hypothesis -- a theory that the living organisms of the biosphere form a single, complex interacting system that creates and maintains a habitable Earth.

Galapagos Islands -- an archipelago on the equator in the Pacific Ocean about 1,000 km west of Ecuador .

Gallbladder -- the pear-shaped reservoir for bile.

Gametes -- mature haploid cells (sperm and ova) that fuse to form a zygote.

Gasohol -- a mixture of gasoline and ethanol.

Gastric acid -- a clear, colorless fluid secreted by the mucous membrane of the stomach, and is the chief agent in digestion.

Gastropods (class Gastropoda) -- snails and other molluscs that typically possess a coiled dorsal shell and a ventral creeping foot.

Gene -- the functional unit of inheritance found on a chromosome.

Gene pool -- a collection of all of the alleles of all of the genes in a population.

Generalists -- animals that are capable of eating a variety of foods or living in a variety of places.

Generalized niche -- a niche that has broad requirements and tolerates a range of conditions.

Genetic drift -- random change in allelic frequencies in a population occurring by chance.

Genetically engineered microorganisms (GEMs) -- bacteria that have been genetically engineered by the insertion or deletion of DNA segments.

Genetics -- the study of the mechanisms of transmission of genes from parents to offspring.

Genome -- all the DNA in a haploid set of chromosomes (nuclear genome), organelle (mitochondrial genome, chloroplast genome) or virus (viral genome, which in some viruses consists of RNA rather than DNA).

Genotype -- a specific combination of genes that determine a character.

Genus -- a group of related species with taxonomic rank between family and species.

Geothermal energy -- energy drawn from the internal heat of the earth, either through geysers, fumaroles, hot springs, or other natural geothermal features, or through deep wells that pump heated groundwater.

Germinate -- to sprout, develop or resume growth and increase metabolic activity.

Gestation period -- the portion of the reproductive cycle in a female mammal extending from fertilization to birth of its offspring.

Gill -- a respiratory organ specialized for gas exchange in aquatic animals.

Gill arches -- bony or cartilaginous gill supports of some vertebrates; also called visceral arches.

Gill cover (or operculum) -- the flap of bony plates that covers the gills of bony fishes.

Gill filaments -- a thin-walled, fleshy extension of a gill arch that contains vessels carrying blood to and from gas exchange surfaces.

Gill raker -- each of the projections along the inner surface of fish gills.

Gill slit -- one of several openings in the pharyngeal region of chordates, which allow water to pass from the pharynx to the outside of the body. In the process, water passes over gills or suspended food is removed in a filter-feeding mechanism.

Ginkgo -- a deciduous gymnosperm tree ( Ginkgo biloba ) with distinctive fan-shaped leaves, native to eastern China .

Girth -- circumference, as of a tree trunk.

Gizzard -- a strong muscular part of a bird’s alimentary canal which enables them to grind their food.

Global warming -- some experts contend our earth's annual average temperature is gradually increasing, partly due to the greenhouse effect.

Glucose -- one of the most abundant simple sugars. It is the building block of both cellulose and starch and is important to several metabolic pathways.

Gluteal -- pertaining to the rump.

Gluten -- a protein complex in endosperm of wheat and some other cereals that is essential in making leavened bread.

Glycogen -- a complex carbohydrate stored in animals.

Gnathostomes (superclass Gnathostomata) -- vertebrates with jaws and paired appendages.

Gonad -- an organ that produces gametes (ovary in the female and testis in the male).

Gondwana -- one of two large continents, the southern one, which formed when the supercontinent Pangaea broke up about 180 million years ago.

Grasslands -- a biome characterized by grasses and a few scattered trees.

Graviportal -- describes an animal built for slow terrestrial locomotion as a result of its comparatively heavy body weight.

Grazer -- an organism that feeds primarily on plants.

Great ocean conveyor -- a global circulation pattern in which water cycles throughout the ocean basins.

Great whales -- the sperm and the baleen whales.

Green algae -- any grass-green, chiefly freshwater algae of the phylum Chlorophyta, often growing on wet rocks, damp wood, or on the surface of stagnant water.

Greenhouse effect -- the warming of the Earth due to the atmospheric accumulation of carbon dioxide and other gases, which trap heat and reradiate it back to the Earth's surface.

Gregarious -- living in groups or flocks.

Gross national product (GNP) -- the sum total of all goods and services produced in a national economy.

Ground itch -- skin rash caused by bacteria introduced by invasive hookworm larvae.

Growth -- an irreversible increase in size or volume of a cell, tissue, organ, or organism.

Growth ring -- a concentric layer of wood (secondary xylem) formed in one growing season through cell divisions of the vascular cambium.

Guano -- the accumulation of the excrement of seabirds or bats.

Gully erosion -- removal of layers of soil, creating channels or ravines.

Gustation -- the act of tasting or the sense of taste.

Gyre -- a large, nearly circular system of wind-driven surface currents that center on latitude 30 in both hemispheres.

H

Habitat -- the place where an organism normally lives or where individuals of a population live.

Hair -- a long slender filament.

Half-life -- the length of time required for half the nuclei in a sample to change into another isotope.

Hallucinogen -- a psychoactive drug capable of altering moods and perceptions of time and space.

Hallux -- the first digit of the foot.

Halophyte -- a salt-tolerant terrestrial plant.

Hardwood -- a term often used in reference to all woody dicots.

Harem -- a large group of females herded by a large male pinniped for the purpose of mating.

Hazardous -- describes chemicals that are dangerous, including flammables, explosives, irritants, sensitizers, acids, and caustics.

Hazardous waste -- any discarded material containing substances known to be toxic, mutagenic, carcinogenic, or teratogenic to humans or other life-forms.

HDL (high density lipoprotein) -- transport molecule that removes excess cholesterol from the body's tissues to the liver for degradation and elimination.

Health -- a state of physical and emotional well-being.

Heartworm disease -- a parasitic infection in dogs caused by the nematode Dirofilaria immitis .

Heavy metals -- a group of toxic metals: mercury, lead, and others.

Hemoglobin -- an iron-containing respiratory pigment occurring in vertebrate red blood cells and in blood plasma of many invertebrates.

Herb -- non-woody plants whose leaves are used in seasoning.

Herbal -- a text that describes plants that are useful medicinally and in other ways.

Herbicide -- a plant growth regulator that inhibits growth or kills a plant when applied at relatively low concentrations.

Herbivore -- animals that feed only on plants.

Heredity -- the transmission of biological traits from parents to their offspring.

Heritable -- capable of being inherited, such as a physical trait.

Hermaphrodite -- an organism with both male and female functional reproductive organs.

Heterodont -- having teeth differentiated into incisors, canines, and molars for different purposes.

Heterotroph -- an organism that is incapable of synthesizing its own food and, therefore, must feed upon organic compounds produced by other organisms.

Hexapoda -- the class of mandibulate arthropods whose members are characterized by having three pairs of legs. Commonly called insects.

Hibernation -- condition, especially of mammals, of passing the winter in a torpid state in which the body temperature drops nearly to freezing and the metabolism drops close to zero.

High tide -- the highest level reached by the rising tide.

Holistic medicine -- the treatment of the whole entity, the human body, spirit, and mind.

Home range -- the area over which an animal ranges in its activities.

Homestead Act -- legislation passed in 1862 allowing any citizen or applicant for citizenship over twenty-one years old and head of a family to acquire 160 acres of public land by living on it and cultivating it for five years.

Homing -- the ability of an animal to return to its home site.

Hominid -- a member of the family Hominidae, now represented by one living species, Homo sapiens.

Homogeneous -- consistent and similar in composition.

Hormone -- 1. an organic molecule synthesized by a plant that exerts, even in low concentrations, profound regulation of growth and/or development. 2. Chemical products of ductless glands that are carried by the circulatory system and that influence various physiological processes in the body.

Horn -- the paired growths on the head of certain ungulate animals; the median growth of hair on the snout of the rhinoceros.

Horseshoe crabs (class Merostomata) -- arthropods with a large horseshoe-shaped carapace.

Host -- an animal or protist that harbors or nourishes another organism (parasite).

Hot desert -- deserts of the American Southwest and Mexico ; characterized by extreme summer heat and cacti.

Human resources -- human wisdom, experience, skill, labor, and enterprise.

Humerus -- the long bone in the upper arm of humans.

Humus -- sticky, brown, insoluble residue from the bodies of dead plants and animals; gives soil its structure, coating mineral particles and holding them together; serves as a major source of plant nutrients.

Hunter-gatherers -- human social groups that secure food sources from wild resources such as hunting animal prey or collecting edible plants from the wild.

Hybrid -- offspring of a cross between two species.

Hydrocarbon -- an organic molecule that contains only carbon and hydrogen and has its carbons bonded in a linear fashion.

Hydroponics -- a system of growing plants in a liquid nutrient solution without soil.

Hydrosphere -- the liquid areas of the earth.

Hydrostatic pressure -- the pressure exerted by a fluid (gas or liquid), defined as force per unit area.

Hydrothermal vents -- deep, oceanic regions where the tectonic plates of the earth's crust are moving apart.

Hydroxyl -- containing an OH- group, a negatively charged ion formed by alkalis in water.

Hydrozoa -- the class of cnidarians whose members include Medusae, when present, with a velum, and Hydra.

Hypha -- the microscopic threads that make up the body of most fungi.

I

Ice age -- a period of time when significant amounts of ice form on the continents causing a correspondent drop in sea level.

Imitation -- an act that occurs when an animal immediately copies the actions of another animal while they are in each other's presence.

Immunity -- a state in which a host is more or less resistant to an infective agent.

Immunization -- the process of making one immune.

Immunology -- the study of the immune system.

Impermeable -- having the property of restricting the passage of substances.

Imprinting -- a process that occurs when an animal learns to make a particular response to only one type of animal or object.

Inbreeding -- the tendency among members of a population to mate preferentially with close relatives.

Incidence -- in epidemiology, the number of new cases of a disease per unit time; that is, a rate measurement.

Incisive -- to cut into.

Independent variables -- the variables that we manipulate to test their effects on behavior.

Indigenous -- pertains to organisms that are native to a particular region; not introduced.

Indo-west Pacific region -- the tropical Indian and west and central Pacific oceans.

Industrial fishery -- a fishery in which the catch is used for purposes other than direct human consumption.

Industrial revolution -- advances in science and technology that have given us power to understand and change our world.

Industrial sewage -- wastewater from industries.

Industrial timber -- trees used for lumber, plywood, veneer, particleboard, chipboard, and paper.

Inferior -- below a point of reference (e.g., the mouth is inferior to the nose in humans).

Infiltration -- the process of water percolation into the soil and pores and hollows of permeable rocks.

Inflammation -- swelling caused by the mobilization of body defenses against foreign substances and infectious agents and the repair of damage from such agents.

Ink sac -- a gland found in some cephalopods that secretes a dark fluid used to discourage predators.

Innate -- a characteristic based partly or wholly factors present in an individual from birth . Inherent.

Inner ear -- a paired, sound-sensitive organ in vertebrates.

Inorganic molecules -- pertaining to compounds that are not hydrocarbons or their derivatives.

Insecticide -- a chemical that kills insects.

Insectivore -- 1. an insectivorous animal or plant. 2. any mammal of the order Insectivora, comprising the moles, shrews, and Old World hedgehogs.

Insects (class Insecta) -- arthropods with three pairs of legs and one pair of antennae.

Instinct -- predictable, genetically programmed behavior.

Instrumental value -- the value or worth of objects that satisfies the needs and wants of moral agents.

Insulin -- a hormone secreted by the pancreas.

Intangible resources -- abstract commodities, such as open space, beauty, serenity, genius, information, diversity, and satisfaction.

Intelligence -- a collection of mental capacities including imagination, problem-solving ability, memory, the ability to use information gained from past experiences, perceptiveness, and behavioral flexibility.

Inter -- meaning between.

International Whaling Commission (IWC) -- an agency that regulates whaling around the world.

Intertidal zone -- the vertical extent of the shoreline between the high and low tide lines.

Intestine -- the convoluted membranous tube which extends from the stomach to the anus and which receives the ingested food from the stomach, mixes it with bile, pancreatic juice and intestinal secretions, and delivers the indigestible products from the system.

Invertebrates -- animals without backbones.

Irrigation -- the application of water to agricultural crops by transporting it to the crop through canals, pipes, and sprinklers.

Irritants -- corrosives (strong acids), caustics (alkaline reagents), and other substances that damage biological tissues on contact.

Ischia -- referring to the hip.

Island effects -- the reduction in species diversity caused by the reduction in ecosystem area.

J

Jacobson's organ -- an olfactory receptor present in most reptiles.

Jawless fishes (class Agnatha) -- fishes that lack jaws and paired fins: hagfishes (or slime eels) and lampreys.

Jet streams -- p owerful winds or currents of air that circulate in shifting flows.

Jugular vein -- the vein in vertebrates that returns blood from the head to the heart.

K

Kelp -- a group of large brown seaweeds.

Keratin -- a tough, water-resistant protein found in the epidermal layers of the skin.

Keystone predator -- a predator that is very important in the maintenance of the structure of a community.

Keystone species -- a species upon which several other species depend.

Kinesis -- the movements by an organism in random directions in response to stimulus.

Kingdom -- the highest level of classification of life.

Krill -- any of the small, pelagic, shrimp-like crustaceans.

L

Lachrymal gland -- a gland beneath the upper eye lid which secretes tears.

Lactation -- the production of milk by the mammary glands.

Lactic acid -- the end product of anaerobic respiration in animals, causes muscle soreness.

Lactose -- milk sugar.

Lagoon -- a shallow, sheltered body of water separated from the open sea by coral reefs, sand bars, and/or barrier islands.

Lancelets (subphylum Cephalochordata) -- chordates with the three basic chordate characteristics but lacking a backbone.

Landfills -- land disposal sites for solid waste.

Large intestine -- that part of the digestive system that removes salt and water from undigested food and releases feces through the anus.

Larva ( pl. larvae) -- the immature, feeding stage of an insect that undergoes metamorphosis.

Larynx (Voice Box) -- the modified upper portion of respiratory tract of air-breathing vertebrates, bounded by the glottis above and the trachea below.

Lateral -- pertaining to the side of an animal; a bilateral animal has two sides.

Lateral-line system -- a line of sensory receptors along the side of some fishes and amphibians used to detect water movement.

Latex -- a milky juice exuded from some plants.

Latitude -- the angular distance north or south of the equator of a position on the earth's surface.

Laurasia -- one of the two large continents, the northern one that formed when the supercontinent Pangaea broke up about 180 million years ago.

Learning -- the relatively permanent change in behavior or potential for behavior that results from experience.

Leeches (class Hirudinea) -- segmented worms that are specialized predators and parasites.

Leeward -- the side away from the direction of a prevailing wind.

Legume -- a simple, dry fruit that splits along two seams, a pod.

Lek -- an area where animals assemble for communal courtship display and mating.

Lentic -- relating to standing water such as a swamp, pond, or lake.

Lesion -- an area of tissue that has been destroyed by an agent such as electric current or a chemical.

Lichen -- a fungus, usually of the class Ascomycetes, that grows symbiotically with algae, resulting in a composite organism that characteristically forms a crust-like or branching growth on rocks or tree trunks.

Life expectancy -- the average number of years lived by a group of individuals after reaching a given age.

Life range -- the larger geographic area that an animal utilizes over the course of its life.

Life span -- the longest period of life reached by a type of organism.

Ligament -- the tough, dense band of connective tissue connecting one bone to another.

Limiting resource -- an essential factor whose short supply prevents the growth of a population.

Limnologist -- a scientist who studies freshwater biology.

Lingual -- pertaining to the tongue.

Lipid -- a fat, oil, or fatlike compound that usually has fatty acids in its molecular structure and is insoluble in water.

Liver -- the largest gland in the human body, which has three functions: it secretes bile, stores glycogen and converts waste products urea and uric acid for excretion.

Liverwort -- a group of the division Bryophyta characterized by a small, inconspicuous, liver-shaped thallus and that lives in moist environments.

Longevity -- the length or duration of life.

Longitude -- the angular distance of a position on the earth's surface east or west of the Greenwich Prime Meridian.

Lumbar -- relating to or near the loins or lower back.

Lumbar vertebrae -- the 5 vertebrae following the thoracic vertebrae.

Lung -- an organ of the respiratory system in which gas exchange occurs between body fluids (e.g., blood) and air.

M

Macroalgae -- the multicellular brown, red, and green algae.

Malignant tumor -- a mass of cancerous cells that have left their site of origin, migrated through the body, invaded normal tissues, and are growing out of control.

Malleus -- a small bone in the middle ear which transmits sound from the tympanum to the incus.

Malnourishment -- a nutritional imbalance caused by lack of specific dietary components or inability to absorb or utilize essential nutrients.

Mammalia -- the class of vertebrates whose members are nursed from mammary glands.

Mammary gland -- in female mammals, the mammary glands produce and secrete milk to nourish developing young.

Mandible -- the lower jaw bone at the front and bottom of the skull in most animals;   t hird pair of appendages from the anterior in Crustacea; second pair in Insecta; primarily function in feeding.

Mange -- dermatitis caused by species of mites.

Mangroves -- shrubs and trees that live along the seashore in tropical and subtropical regions and tolerate inundation by seawater.

Maniraptora ("hand robbers") -- a group of animals defined as birds and all taxa closer to birds than to Ornithomimus . It should be noted that this is not a grouping of dinosaurs that may include birds; it is a grouping of birds that may include certain dinosaurs.

Marine -- living in or pertaining to the sea.

Marsh -- a type of wetland characterized by simple plant life and without trees.

Marsupials -- families of mammals, such as kangaroos and opossums, whose females carry their young in an external pouch.

Masseter -- the human muscle which moves the mandible for chewing.

Mastication -- chewing.

Maternal -- pertaining to the mother.

Matrix -- a substance in which rocks, minerals, fossils or other similar materials are embedded. In paleontology, matrix is the rock in which a given fossil is embedded.

Maturation -- to complete the natural development of an animal system.

Maxillae -- the bone comprising the upper jaw in the human skull.

Maximum sustainable yield -- the maximum level of fishing effort that a fish stock can withstand without causing major upsets in the abundance of its stock.

Meadow -- an open clearing in a landscape in which low-growing plants dominate.

Medial -- on or near the plane that divides a bilateral animal into mirror images.

Mediated transport -- the t ransport of a substance across a cell membrane mediated by a carrier molecule in the membrane.

Mediportal -- describes an animal built primarily for slow terrestrial locomotion as a result of its comparatively heavy body weight, but with a few adaptations for speed.

Mediterranean climate areas -- specialized landscapes with warm, dry summers and cool, wet winters.

Medulla -- the inner portion of an organ in contrast to the cortex or outer portion.

Medulla oblongata -- the portion of the brain stem located between the pons and the spinal cord.

Medusa -- a jellyfish or the free-swimming stage in the life cycle of cnidarians.

Meiosis -- the process of cell division by which egg and sperm cells are formed, involving a diminution in the amount of genetic material.

Melanin -- black or dark-brown pigment found in plant or animal structures.

Melanism -- dark coloration of the skin, fur, or feathers because of the presence of the pigment melanin.

Membrane -- in living organisms, a layer of tissue that functions as a partition of cellulose activities.

Menopause -- in the human female, that time of life when ovulation ceases.

Menstrual cycle -- the period of the regularly recurring physiologic changes in the endometrium that culminates in its shedding (menstruation).

Menstruation -- the loss of blood and tissue from the uterus at the end of a female primate's reproductive cycle.

Mesozoa -- a phylum of animals whose members are parasites of marine invertebrates.

Mesozoic -- the geological era beginning about 250 million years ago.

Messenger RNA -- formed in the nucleus from a DNA template and carries the transcribed genetic code to the ribosome where the genetic code is translated into protein.

Metabolism -- a group of processes that includes digestion, production of energy (respiration), and synthesis of molecules and structures by organisms.

Metacyst -- the cystic stage of a parasite that is infective to a host.

Metamorphosis -- a type of development in which one or more juvenile types differ markedly in body form from the adult.

Metaphase -- a stage in mitosis when chromosomes become aligned in the middle of the cell and firmly attached to the mitotic spindle but have not yet segregated toward opposite poles.

Metathorax -- the posterior of the three segments of an insect thorax.

Metazoa -- multicellular animals.

Methane ( CH4) -- natural gas.

Microscopy -- examination with a microscope.

Migration -- a seasonal movement from one location to another.

Mimicry -- when one species resembles one or more other species.

Mineral -- a naturally occurring, inorganic, crystalline solid with definite chemical composition and characteristic physical properties.

Mississippian -- part of the Carboniferous period, beginning around 360 million years ago.

Mitochondria -- in eukaryotes, a sub-cellular organelle that conducts cellular respiration.

Mitosis -- cell reproduction by indirect division. It is the common method of division in the higher animals. It is characterized by a series of complex changes in the nucleus leading to its subdivision. The process takes between 30 minutes and a few hours, and is comprised of 4 stages: prophase, metaphase, anaphase and telophase.

Molar -- a grinder tooth.

Mollusca -- the phylum of animals whose members possess a head-foot, visceral mass, mantle, and mantle cavity. Most molluscs also possess a radula and a shell.

Molt -- a process whereby an organism sheds its outer exoskeleton or skin periodically as it grows. Also refers to changing the pelage or feathers in a mammal or bird.

Monera -- the kingdom of life whose members are characterized by having cells that lack a membrane-bound nucleus, as well as other internal, membrane-bound organelles (they are prokaryotic); bacteria.

Monocot -- one of the two primary groups of angiosperms characterized by a single cotyledon, parallel venation of leaves, and floral parts in threes.

Monogamy -- the condition of having a single mate at any one time.

Monomer -- a molecule of simple structure, but capable of linking with others to form polymers.

Monophyletic -- describes a taxon that contains all the descendant organisms of its common ancestor.

Monospecific -- describes a grouping, assemblage, collection, etc., that is comprised of only one species.

Monotremes -- mammals, such as the platypus and echidna, that lay eggs, but nurse their young.

Monsoon -- a seasonal reversal of wind patterns caused by the different heating and cooling rates of the oceans and continents.

Montane coniferous forests -- coniferous forests of the mountains consisting of belts of different forest communities along an altitudinal gradient.

Morbidity -- illness or disease.

Morphine -- a pain-relieving and addictive compound derived from the opium poppy.

Mortality -- the death rate in a population.

Moss -- a group of terrestrial, nonvascular plants.

Mucus -- a thick slippery secretion produced by secretory cells in mucous membranes that act as a protective barrier, lubricant and carrier of enzymes.

Mud flat -- a muddy bottom that is exposed at low tide.

Mulch -- a protective ground cover that inhibits weed growth and protects the soil.

Muscle tissue -- the type of tissue made of bundles of long cells that allows movement.

Mushroom -- the common name for a group of fungi that produce an aboveground reproductive structure.

Mutagens -- agents, such as chemicals or radiation, which damage or alter genetic material (DNA) in cells.

Mutation -- a change, either spontaneous or by external factors, in the genetic material of a cell.

Mutualism -- a type of interaction in which two different species derive benefit from their association and in which the association is necessary to both.

Mycologist -- a person who studies fungi.

Myiasis -- an infection by fly maggots.

Myxini -- the class of vertebrates whose members are fishlike, jawless, without paired appendages, and possess four pairs of tentacles around the mouth.

N

Natal -- pertaining to birth.

Native species -- a local species that has not been introduced.

Natural history -- the study of where and how organisms carry out their life cycles.

Natural resources -- goods and services supplied by the environment.

Natural selection -- the mechanism for evolutionary change in which environmental pressures cause certain genetic combinations in a population to become more abundant.

Natural Selection -- the process in evolution by which those individuals of a species with characters that help them to become adapted to their specific environment tend to transmit their characters, while those less able to become adapted tend to die out.

Navigation -- the process by which an animal uses various cues to determine its position in reference to a goal.

Neap tides -- small tides that occur around the quarter moon.

Necrosis -- cell or tissue death.

Nectar -- a sweet syrup produced by some flowers as an attractant for pollinators.

Nematocyst -- the stinging structure of cnidarians.

Nematodes (or roundworms; phylum Nematoda) -- invertebrates with a cylindrical body, a conspicuous body cavity, and a complete digestive tract.

Neolithic -- the Stone Age period following the advent of agriculture.

Nephric -- pertaining to the kidney.

Nerve -- a bundle of neurons or nerve cells outside the central nervous system which generate and transmit electrical impulses. .

Nerve cell -- a cell specialized to originate or transmit nerve impulses.

Nerve cord -- a long, compact bundle of nerve cells that is part of the central nervous system.

Nervous tissue -- the type of tissue composed of individual cells called neurons.

Neuron -- a nerve cell that consists of a cell body and its processes.

Neurotoxins -- toxic substances, such as lead or mercury, that specifically poison nerve cells.

Neurotransmitter -- a chemical substance secreted by the terminal end of an axon that stimulates a muscle fiber contraction or an impulse in another neuron.

Nictitating membrane -- a third eyelid, found on many birds and reptiles, consisting of a transparent membrane that can be pulled across the eye.

Nitrous oxide (NO 2 ) -- an atmospheric gas that traps infrared radiation and also can form nitric acid in rain droplets, resulting in acid rain.

Nocturnal -- animals whose primary activity occurs at night in darkness.

Node -- the point on a stem at which leaves and buds are attached.

Nodule -- a tumor-like growth on the roots of certain higher plants that encloses a population of nitrogen-fixing bacteria.

Nomenclature -- the study of the naming of organisms in the fashion that reflects their evolutionary relationships.

Nonpoint sources -- scattered, diffuse sources of pollutants, such as runoff from farm fields, golf courses, construction sites, etc.

Nonrenewable resources -- materials or services from the environment that are not replaced or replenished by natural processes at a rate comparable to our use of the resource.

Northern coniferous forest -- the biome characterized by cool summers, cold winters, and short growing seasons.

Notochord -- an elongated cellular cord, enclosed in a sheath, which forms the primitive axial skeleton of chordate embryos and adult cephalochordates.

Nudibranchs (sea slugs) -- gastropods that lack a shell and have exposed gills.

Nut -- a dry and usually one-seeded fruit with a hard shell.

Nutrient -- a raw material other than carbon dioxide and water that is needed by an autotroph to produce organic matter.

Nutrition -- the study of the sources, actions, and interactions of nutrients.

O

Obligate Biped -- describes an animal whose anatomy requires it to use only its two hind limbs in walking or similar locomotion.

Obligate Quadruped -- describes an animal whose anatomy requires it to use all four limbs in walking or similar locomotion.

Oceanic -- pertaining to the portion of the marine environment that overlies the deep ocean basins.

Oceanic zone -- the pelagic environment beyond the shelf break.

Oil -- a triglyceride that is liquid at room temperature.

Olecranon -- the elbow.

Olfactory -- pertaining to the sense of smell.

Omnivore -- an animal that uses a variety of animal and plant material in its diet.

Open canopy -- a forest where tree crowns cover less than 20 percent of the ground; also called woodland.

Open circulatory system -- a circulatory system in which blood is not confined to vessels in a part of its circuit within an animal.

Open range -- unfenced, natural grazing lands; includes woodland as well as grassland.

Open system -- a system that exchanges energy and matter with its environment.

Optic -- the eye.

Oral -- the end of an animal containing the mouth.

Orbits -- a pair of roomy cavities in the skull which contain the eyes.

Order -- a taxonomic rank consisting of a group of related families.

Ordovician -- a geological period beginning around 500 million years ago.

Organ -- a structure composed of different tissues, such as a heart, liver or lungs.

Organ system -- a set of interconnected or interdependent parts that function together in a common purpose or produce results that cannot be achieved by one of them acting alone.

Organelle -- a body within the cytoplasm of eukaryotic cells; several different types of organelles occur, each with a specialized function such as the chloroplast, which functions in photosynthesis.

Organic -- living or once living material; compounds containing carbon formed by living organisms.

Organic compound -- a molecule that contains carbon, hydrogen, and usually oxygen.

Organic molecule -- a molecule that contains one or more carbon atoms.

Organism -- an individual member of a species; a single biological entity.

Ornithischia ("bird hips") -- formerly the major grouping of dinosaurs that is comprised of the beaked dinosaurs.

Osmosis -- the movement of water through a permeable membrane.

Osteichthyes -- the class of (Bony) fishes whose members are characterized by the presence of a bony skeleton, a swim bladder, and an operculum.

Ovary -- the primary reproductive organ of a female; where eggs (ova) are produced.

Overpopulation -- too many organisms in an area for the available resources to support in a sustainable way.

Overturn -- the sinking of surface water that has become denser than the water below.

Oviparity -- a condition that describes the habit of releasing eggs that later hatch.

Oviparous -- an animal that releases eggs.

Ovulation -- the release of an egg from the ovary.

Ovum -- mature female germ cell (egg).

Oxygen -- an element that is one of the constituents of water, organic matter, and many other chemicals. Oxygen gas (O 2 ), composed of two oxygen atoms, is needed for respiration and is produced by photosynthesis.

Oyster reef -- a dense oyster bed present in some estuaries and other marine environments.

Ozone -- a highly reactive molecule containing three oxygen atoms; a dangerous pollutant in ambient air. In the stratosphere, however, ozone forms an ultraviolet absorbing shield that protects us from mutagenic radiation.

Ozone layer -- a layer of ozone (O 3 ) in the atmosphere that deflects harmful ultraviolet radiation.

P

Pain receptor -- a modified nerve ending that, when stimulated, gives rise to the sense of pain.

Palatal -- the palate or roof of the mouth.

Paleolithic -- Old Stone Age; a cultural period during which early humans obtained food solely by foraging; ending in some areas approximately 10,000 years ago.

Paleontologist -- a person who studies fossils and all aspects of extinct life.

Paleontology -- the study of early life-forms on earth.

Paleozoic -- the geological era beginning 590 million years ago and ending about 250 million years ago.

Palmar -- the front foot pads.

Pancreas -- a gland located in the abdomen that produces both digestive enzymes (exocrine pancreas) and hormones (endocrine pancreas). Key hormones produced by the pancreas are insulin and glucagon, which play roles in regulating blood glucose levels.

Pandemic -- a very widely distributed epidemic.

Para -- beside or near.

Parallelism -- an evolutionary pattern that results in the formation of homologous character states. The similar body forms of Old World Monkeys and New World Monkeys are due to their having a common ancestor; their similar body forms are due to parallel evolution rather than convergence.

Paraphyletic -- describes a taxon that does not contain all the descendant species or taxa of their common ancestor.

Parasite -- an organism that lives in or on another organism, deriving nourishment at the expense of its host, usually without killing it.

Parasitic -- an association where one living organism benefits at the expense of another.

Parasitism -- the condition of an organism living in or on another organism (host) at whose expense the parasite is maintained.

Parasitoid -- an organism that is a typical parasite early in its development but that finally kills the host during or at the completion of development.

Parthenogenesis -- Unisexual reproduction involving the production of young by females not fertilized by males.

Parts per billion (ppb) -- the number of parts of a chemical found in one billion parts of a particular gas, liquid, or solid mixture.

Parts per million (ppm) -- the number of parts of a chemical found in one million parts of a particular gas, liquid, or solid mixture.

Parts per trillion (ppt) -- the number of parts of a chemical found in one trillion parts of a particular gas, liquid, or solid mixture.

Pasture -- enclosed domestic meadows or managed grazing lands.

Patella (kneecap) -- a flattened, triangular bone situated in front of the knee-joint.

Pathogen -- an organism that produces disease in a host organism.

Peat moss -- a relatively sterile, inert medium composed of partially decomposed plants of the genus Sphagnum.

Peck order -- a hierarchy of social privilege in a flock of birds.

Pectoral -- pertaining to the breast or chest; to the pectoral girdle; or to a pair of horny shields of the plastron of certain turtles.

Pectoral fin -- each of the pair of fins just behind the head of fishes.

Pelage -- the hairy covering of mammals.

Pelagic -- pertaining to the open ocean.

Pelagic organism -- an organism that lives above the bottom in the open sea.

Pelvic -- situated at or near the pelvis, as applied to girdle, cavity, fins, and limbs.

Pelvic fin -- each of the second pair of ventral fins of fishes.

Pelvis -- a bony girdle in vertebrates that connects the body with the lower extremities.

Penicillin -- an antibiotic produced by certain species of Penicillium.

Pennsylvanian -- a geological period of the Carboniferous beginning about 320 million years ago.

Pentadactyl -- with five digits, or five fingerlike parts, to the hand or foot.

Pericardium -- the area or membrane around heart.

Period -- the duration of one cycle of a biological rhythm.

Perissodactyl -- an order of ungulate mammals with an odd number of digits.

Permafrost -- the permanently frozen soil in Polar Regions .

Permeability -- a property of membranes allowing all substances to pass freely.

Permian -- the last geological period of the Paleozoic era beginning about 286 million years ago and ending 251 million years ago.

Pest -- any organism that reduces the availability, quality, or value of a useful resource.

Pesticide -- any chemical that kills, controls, drives away, or modifies the behavior of a pest.

Petal -- the often showy flower component attached just inside the sepals; petals are usually colorful to attract pollinators.

Petiole -- the stalk of a leaf.

Petrifaction -- a fossil formed when plant parts are infiltrated or replaced by mineral substances such that the structure is preserved but the fossil is actually rock.

Petroleum products -- oil and the materials made from crude natural petroleum.

Phaeophyta -- the group of organisms commonly termed the brown algae, consisting of about 1500 species, including the kelps.

Phagotroph -- a heterotrophic organism that ingests solid particles for food.

Phalanges -- the bones of the human digits (fingers).

Phase -- a specified, recognizable portion of the activity cycle.

Pheromone -- a chemical substance released by one organism that influences the behavior or physiological processes of another organism.

Photic zone -- the surface layer where there is enough light for photosynthesis to occur.

Photophore (light organ) -- an organ that produces bioluminescence.

Photopigment -- a molecule in visual receptor cells that responds to light energy.

Photosynthesis -- the process by which green plants and some bacteria capture light energy and use it to produce food.

Phototropism -- the bending of a plant toward a unidirectional light source.

Phylogenetic tree -- a branching diagram depicting the evolutionary relationships between major groups of organisms.

Phylogeny -- the evolutionary development and history of a species or higher taxonomic grouping of organisms. The phylogeny of an organism is sometimes called a "family tree."

Phylogeny -- the origin and diversification of any taxon, or the evolutionary history of its origin and diversification.

Phylum -- a chief category, between kingdom and class, of taxonomic classifications into which are grouped organisms of common descent that share a fundamental pattern of organization.

Pigments -- molecules that reflect and absorb light at particular wavelengths.

Pinniped (order Pinnipedia) -- the mammals with paddle-shaped flippers: seals, eared seals (sea lions and fur seals), and the walrus.

Pistil -- the female reproductive part of a flower, consisting of stigma, style, and ovary.

Pit organ -- a heat receptor on the head of some snakes (pit vipers).

Pituary gland -- a gland within the brain concerned with regulating growth and regulating other ductless glands.

Placenta -- a s tructure which a fetus is attached to its mother's uterine wall and through which it is nourished.

Placoid scale -- a type of scale found in cartilaginous fishes, with basal plate of dentin embedded in the skin and a backward-pointing spine tipped with enamel.

Planktivore -- an animal that feeds on plankton.

Plankton -- animals (zooplankton) and unicellular algae (phytoplankton) that have only limited locomotory capabilities and are therefore distributed by water movements.

Plantae -- one of the five kingdoms of life; characterized by being eukaryotic and multicellular, and having rigid cell walls and chloroplasts.

Plantar -- the rear foot pads.

Plasma -- the liquid part of the blood.

Plastron -- the ventral body shield of turtles; a structure in corresponding position in certain arthropods; or, the thin film of gas retained by epicuticle hairs of aquatic insects.

Platelet -- a tiny, incomplete cell in the blood that releases substances initiating blood clotting.

Play behavior -- certain locomotor, social, and manipulative behavior patterns exhibited by young and some adult mammals and birds.

Pleistocene -- a geological period, which began about 2 million years ago, characterized by a series of ice ages.

Plesiomorph -- an evolutionarily primitive character state. The long neck of the giraffe is apomorphic; the short neck of its ancestor is plesiomorphic.

Poachers -- those who hunt wildlife illegally.

Pod --1. A dry dehiscent fruit that splits along two seams; a legume.2. A school of cetaceans.

Point sources -- specific locations of highly concentrated pollution discharge, such as factories, power plants, sewage treatment plants, underground coal mines, and oil wells.

Polar easterlies -- variable winds that blow at high latitudes.

Polar ice cap -- the portions of the globe close to the poles that are permanently covered with ice.

Pollen -- the collective term for pollen grains, the male gametophytes.

Pollen grain -- the structure into which a haploid microspore develops; contains a haploid tube nucleus and two haploid sperm nuclei at maturity.

Pollination -- the transfer of pollen to a receptive surface; the stigma in angiosperms or the pollination droplet in most gymnosperms.

Pollinator -- an organism that effects pollination.

Polyandrous -- having more than one male mate.

Polygamy -- the condition of having more than one mate at a time.

Polyp -- individual of the phylum Cnidaria, generally adapted for attachment to the substratum at the aboral end, often form colonies.

Polyunsaturated fat -- a fat having several to many double bonds between carbon atoms.

Pongid -- relating to the primate family Pongidae, comprising the anthropoid apes (gorillas, chimpanzees, gibbons, orangutans).

Population -- a group of organisms of the same species inhabiting a specific geographical locality.

Population crash -- a sudden population decline caused by predation, waste accumulation, or resource depletion; also called a dieback.

Population explosion -- growth of a population at exponential rates to a size that exceeds environmental carrying capacity; usually followed by a population crash.

Porifera -- the animal phylum whose members are sessile and either asymmetrical or radially symmetrical. Body organized around a system of water canals and chambers. Cells are not organized into tissues or organs. Sponges.

Postanal tail -- a tail that extends posterior to the anus; one of the four unique characteristics of chordates.

Posterior -- situated at or toward the rear of the body; situated toward the back; in human anatomy the upright posture makes posterior and dorsal identical.

Prairie -- an area of land dominated by grasses with occasional shrubby plants and small trees occurring where the grass cover is broken and with herbaceous perennials during certain seasons.

Precambrian -- the geological era beginning with the formation of the earth, about 4700 million years ago and extending until about 590 million years ago.

Precocial -- describes organisms that are born capable of surviving with little or no parental care.

Predation -- the ingestion of prey by a predator for energy and nutrients.

Predator -- an organism that preys on other organisms for its food.

Predentata ("predentary-boned (dinosaurs)") -- major grouping of dinosaurs that is comprised of the beaked dinosaurs. Formerly called the Ornithischia.

Prehensile -- adapted for grasping.

Primary consumer -- an organism that consumes a producer organism as a food source; a herbivore.

Primary pollutants -- chemicals released directly into the air in a harmful form.

Primary productivity -- the synthesis of organic materials (biomass) by green plants using the energy captured in photosynthesis.

Primate -- any mammal of the order Primates, which includes the tarsiers, lemurs, marmosets, monkeys, apes, and humans.

Primitive -- primordial; ancient; little evolved; describes a character state in the common ancestor of a taxon.

Principle of competitive exclusion -- a result of natural selection whereby two similar species in a community occupy different ecological niches, thereby reducing competition for food.

Pristine -- a natural and undisturbed state.

Proboscis -- a snout or trunk, or a tubular sucking or feeding organ with the mouth at the end as in planarians, leeches, and insects, or the sensory and defensive organ at the anterior end of certain invertebrates.

Producers -- organisms, such as plants, able to produce their own food from inorganic substances.

Production -- in ecology, the energy accumulated by an organism that becomes incorporated into new biomass.

Profundal zone -- the deepest portion of a lake.

Progesterone -- a hormone that regulates the menstrual cycle in vertebrates.

Proglottid -- one set of reproductive organs in a tapeworm strobila; usually corresponds to a segment

Prokaryote -- an organism in which the chromosomes are not contained within membrane-bound nuclei.

Propagation -- the process of increasing in number.

Prophase -- the 1st stage in mitosis cell reproduction. The nucleolus disappears and a number of chromosomes become apparent.

Protective coloration -- coloration that benefits the individual by providing concealment from predators.

Protein -- a macromolecule of carbon, hydrogen, oxygen, and nitrogen and sometimes sulfur and phosphorus; composed of chains of amino acids joined by peptide bonds; present in all cells.

Protista -- the kingdom whose members are characterized by being eukaryotic and unicellular or colonial.

Protogyny -- a sequentially hermaphroditic species in which individuals change from females to males.

Protoplasm -- an organized living substance; cytoplasm and nucleoplasm of the cell.

Protozoa -- a subkingdom (formerly a phylum) comprising the simplest organisms called Protista.

Proximal -- toward the body.

Pruning -- the selective removal of parts of a plant, usually woody shrubs or trees.

Pseudopodia -- the temporary cytoplasmic extensions of amoebas that are used in feeding and locomotion.

Pterosauria ("winged lizards") -- a group of animals, partly distinguished by a greatly elongated fourth finger that supported a membranous wing, that first evolved in the latter third of the Triassic and survived until the end of the Cretaceous. Pterosaurs were not dinosaurs, but were closely related to both dinosaurs and crocodiles.

Puberty -- the age at which an organism can first reproduce.

Pulmonary -- associated with lungs.

Pulping -- the process of partially digesting and breaking up wood fibers to make paper.

Pupa -- the inactive stage of insects. It follows the larval stages and precedes the adult stage.

Q

Quadriceps -- a muscle of the thigh that extends the leg.

Quadrupeds -- animals that walk on four legs.

Queen -- in entomology, the single fully developed female in a colony of social insects such as bees, ants, and termites, distinguished from workers, non-reproductive females, and soldiers.

R

Radial symmetry -- a morphological condition in which the parts of an animal are arranged concentrically around an oral-aboral axis, and more than one imaginary plane through this axis yields halves that are mirror images of each other.

Radius -- one of the two long bones which form the human lower arm.

Rain forest -- a forest with high humidity, constant temperature, and abundant rainfall (generally over 380 cm [150 in] per year); can be tropical or temperate.

Rain shadow -- dry area on the downwind side of a mountain.

Rangeland -- grasslands and open woodlands suitable for livestock grazing.

Recessive -- a gene whose expression is masked when it is present in combination with a dominant allele.

Recessive gene -- a gene that is masked by its dominant allelic partner, having the recessive phenotype expressed only when both alleles for a given trait are recessive.

Recessive trait -- a trait caused by an allele, the phenotype of which is suppressed when it occurs with the dominant allele. Hence, two recessive alleles are necessary for the recessive phenotype to be displayed.

Recolonization -- the reestablishment of a natural community following a natural or unnatural event that removed the existing community.

Recombinant DNA -- the incorporation of DNA from one organism into that of another organism (usually a bacteria) so that the second organism produces a desired protein.

Rectum -- the lowest portion of the large intestine terminating at the anus.

Recycling -- reprocessing of discarded materials into new, useful products; not the same as reuse of materials for their original purpose, but the terms are often used interchangeably.

Red algae -- seaweeds that have a predominance of red pigments.

Red blood cell (erythrocyte) -- the type of blood cell that contains hemoglobin and no nucleus. During their formation in mammals, erythrocytes lose their nuclei; those of other vertebrates retain the nuclei.

Red tide -- a population explosion or bloom of minute, single-celled marine organisms called dinoflagellates. Billions of these cells can accumulate in protected bays where the toxins they contain can poison other marine life.

Refuse-derived fuel -- the processing of solid waste to remove metal, glass, and other unburnable materials; organic residue is shredded, formed into pellets, and dried to make fuel for power plants.

Regeneration -- the ability of an organism to grow a body part that has been lost.

Regulations -- the rules established by administrative agencies; regulations can be more important than statutory law in the day-to-day management of resources.

Reinforcement -- in learning, anything that alters the probability of behavior.

Renal -- refers to the kidney.

Renewable resources -- resources normally replaced or replenished by natural processes; resources not depleted by moderate use; examples include solar energy, biological resources such as forests and fisheries, biological organisms, and some biogeochemical cycles.

Reproductive success -- the number of progeny born, or surviving progeny produced by an organism.

Reptiles (class Reptilia) -- vertebrates with scales on their skin and leathery eggs that are laid on land. Marine reptiles include sea turtles, sea snakes, the marine iguana, and the saltwater crocodile.

Reptilia -- all descendants of the most recent common ancestor of turtles, lepidosaurs (tuataras and squamates), and archosaurs (crocodilians and birds).

Reptilia -- the class of vertebrates whose members have dry skin with epidermal scales and amniotic eggs that develop in terrestrial environments. Snakes, lizards, and alligators.

Resilience -- the ability of a community or ecosystem to recover from disturbances.

Resistance (inertia) -- the ability of a community to resist being changed by potentially disruptive events.

Resource scarcity -- a shortage or deficit in some resource.

Respiration -- the gaseous interchange between an organism and its surrounding medium. In the cell, the release of energy by the oxidation of food molecules.

Reticular -- resembling a net in appearance or structure.

Retina -- the posterior sensory membrane of the eye that receives images.

Revegetate -- the natural or induced replacement of plants into a cleared area; the recurrence of the same plant community that existed prior to clearing.

Ribosome -- a subcellular structure composed of protein and ribonucleic acid. May be free in the cytoplasm or attached to the membranes of the endoplasmic reticulum; functions in protein synthesis.

Risk -- the probability that something undesirable will happen as a consequence of exposure to a hazard.

Ritualization -- in ethology, the evolutionary modification, usually intensification, of a behavior pattern to serve communication.

RNA -- ribonucleic acid; nucleic acid used for transcription and translation of the genetic code found on DNA molecules.

Rockweeds -- a type of brown algae such as Fucus that are inhabitants of rocky shores in temperate zones.

Rod cell -- a type of light receptor that is responsible for color vision.

Root system -- the portion of the plant formed from the growth of the radicle and its subsequent branching; generally the underground portion of the plant.

Rorquals -- the baleen whales that display long grooves on the underside.

Ruminant animals -- the cud-chewing animals, such as cattle, sheep, goats, and buffalo, with multi-chambered stomachs in which cellulose is digested with the aid of bacteria.

Rural area -- an area in which most residents depend on agriculture or the harvesting of natural resources for their livelihood.

S

Sacrum -- the bone formed by fused vertebrae to which pelvic girdle is attached; pertaining to the sacrum.

Salinity -- the amount of dissolved salts (especially sodium chloride) in a given volume of water.

Salinization -- a process in which mineral salts accumulate in the soil, killing plants; occurs when soils in dry climates are irrigated profusely.

Saliva -- a secretion from the salivary glands in the oral cavity. It contains mucus to lubricate food and enzymes.

Salmon ranching -- the practice in which cultured juvenile salmon are released into fresh water and allowed to migrate to sea so they can be harvested later when they return as adults.

Salt wedge -- a layer of denser, saltier seawater that flows along the bottom in estuaries .

Sand dollars -- sea urchins with a flat, round test and short spines that live partly buried in soft sediments.

Saprophyte -- a plant living on dead or decaying organic matter.

Sargasso Sea -- the region of the Atlantic Ocean north of the West Indies that is characterized by floating masses of Sargasso weed, a brown alga.

Saturated fat -- a fat in which all the carbons in the fatty acids are connected by single bonds, thereby having the maximum number of hydrogen atoms.

Saurischia ("lizard hips") -- a major grouping of dinosaurs that is comprised of theropods and sauropods. Gauthier (1986) formally defined Saurischia as birds and all taxa closer to birds than to Ornithischia (Predentata).

Sauropoda ("lizard feet") -- comprised of quadrupedal, plant eating saurischians.

Savanna -- a biome found between the tropics and deserts composed of extensive grasslands with scattered deciduous trees.

Scabies -- a disease caused by mites of the genus Sarcoptes.

Scale -- a thin, compacted, flaky fragment.

Scanning electron microscope -- the type of microscope in which an electron beam, instead of light, forms a three-dimensional image for viewing, allowing much greater magnification and resolution.

Scansorial -- an animal with unspecialized limbs allowing it to grasp and climb as well as walk and run.

Scapula -- refers to the shoulder blade.

Scavenger -- an animal that feeds on dead organic matter.

Scent gland -- a gland located around the feet, face, or anus of many mammals; secretes pheromones, which may be involved with defense, species and sex recognition, and territorial behavior.

School -- a well-defined social organization of marine animals consisting of a single species with all members of a similar size.

Sciatic -- refers to the hip.

Scientific name -- a binomial (genus and species) unique to each identified organism.

Scolex -- the attachment or holdfast organ of a tapeworm, generally considered the anterior end; it is used to adhere to the host.

Scoliosis -- the lateral curvature of the spine.

Scrotum -- the pouch that contains the testes in most mammals.

Scuba (self-contained underwater breathing apparatus) -- the use of tanks of compressed air for breathing underwater. Invented by the late Jacques Yves Cousteau.

Scyphozoans -- Cnidarians whose life cycle includes a conspicuous medusa and a much reduced or absent polyp.

Sea anemones -- Anthozoans that consist of one large polyp.

Sea cucumbers -- Echinoderms with a soft, elongate body that lacks spines.

Sea squirts -- Tunicates with a sac-like, attached body as adults.

Sea stars -- Echinoderms with five or more radiating arms and tube feet that are used in locomotion.

Sea urchins -- Echinoderms with a round or flattened test and movable spines.

Seasonal -- fluctuations in environmental factors such as temperature over an annual cycle.

Sebaceous glands -- ducts in the skin which secrete oil to lubricate the skin and hair.

Second World -- the industrialized, socialist, centrally planned economy nations of Eastern Europe and the former Soviet Union and its allies.

Secondary consumer -- an animal that feeds on other consumers.

Secondary pollutants -- chemicals that become hazardous after entering the air or that are formed by chemical reactions as components of the air mix and interact.

Secondary succession -- the revegetation of cleared land.

Secretin -- a hormone produced by the small intestine in vertebrates that stimulates the production of digestive secretions.

Secure landfill -- a solid waste disposal site lined and capped with an impermeable barrier to prevent leakage or leaching. Drain tiles, sampling wells, and vent systems provide monitoring and pollution control.

Sedatives -- compounds that produce a relaxed, euphoric state--opium and its derivatives, morphine and heroin, are sedatives.

Seed -- a matured ovule containing an embryo and food supply and covered by a seed coat.

Seed coat -- the outer layer of a seed that is developed from the integuments of the ovule; the testa.

Segmented worms -- invertebrates that display an elongate body with distinct segmentation and a digestive tract that lies in a coelom.

Selective cutting -- harvesting only mature trees of certain species and size; usually more expensive than clear-cutting, but it is less disruptive for wildlife and often better for forest regeneration.

Self-pollination -- the transfer of pollen from stamen to stigma within the same plant.

Self-regulating population -- a population with a growth rate that is dependent on its own numbers.

Semen -- the thick, whitish secretion of the reproductive organs in the male; composed of sperm and secretions from the prostate, seminal vesicles, and various other glands and ducts.

Semicircular canals -- the bony canals in the vertebrate inner ear.

Semidiurnal tide -- a tidal pattern with two high and two low tides each day.

Semipermeable -- permeable to small particles, such as water and certain inorganic ions, but not to larger molecules.

Sensation -- the process of transducing environmental stimuli or energy into action potentials.

Sensory deprivation -- withholding all or a specified portion of the sensory input that an animal would normally be receiving.

Sensory filter -- neural circuits that selectively transmit some features of a sensory input and ignore other features.

Sensory neuron -- a neuron that is modified to respond to a particular set of stimuli.

Septicemia -- a systemic infection where a pathogen is present in the circulating blood.

Septum -- a wall between two cavities, particularly separating the two sides of the human heart.

Serum -- the liquid that separates from the blood after coagulation; blood plasma from which fibrinogen has been removed.

Sessile -- fixed to one spot, not able to move about.

Sex chromosome -- one of a pair of chromosomes whose composition determines gender.

Sex hormone -- A hormone that controls the timing of reproduction and sexual characteristics in vertebrates.

Sex-influenced traits -- traits that behave as if they are dominant in one sex but recessive in the other sex.

Sexual reproduction -- the form of reproduction involving the fusion of gametes.

Sexual selection -- the selection process in relation to mating. It is composed of intra-sexual competition among members of one sex (usually males) for access to the other sex and inter-sexual choice of members of one sex by members of the other sex (usually females).

Shattering -- a trait found in wild plants in which the fruiting head breaks apart to scatter the seeds over a wide area.

Shell -- the calcium carbonate outer layer of cnidarians, mollusks, and other Animals. Produced by mucous glands.

Short grass prairie -- a grassland biome characterized by short grass and low rainfall; also known as the plains.

Siblicide -- the killing of one sibling by another.

Silica (SiO3) -- a mineral similar to glass that is the major component of the cell wall, shell, or skeleton of many marine organisms.

Silurian -- the geological period beginning about 435 million years ago during which time the first land plants occurred.

Simian -- pertaining to monkeys or apes.

Sinus -- a cavity or space in tissues or in bone.

Siphon -- a tubular structure through which fluid flows; siphons of some mollusks allow water to enter and leave the mantle cavity.

Skeletal muscle -- a type of muscle tissue found in muscles attached to skeletal parts.

Skeleton -- the hard internal or external framework of bone s, cartilage or shell which: provides protection for animal’s organs, provides fixing points for the muscles, and a general frame for the body.

Skin -- the outer covering of an animal body, consisting of the dermis and the epidermis and resting on the subcutaneous tissues.

Sleeping sickness -- a disease carried by the Tsetse fly of Africa that left untreated can be fatal.

Sludge -- a semisolid mixture of organic and inorganic materials that settles out of wastewater at a sewage treatment plant.

Small intestine -- the part of the digestive system consisting of the duodenum, jejunum, and ileum.

Smog -- the term used to describe the combination of smoke and fog in the stagnant air of London ; now often applied to photochemical pollution products or urban air pollution of any kind.

Smolt -- a young salmon just before it migrates downstream and out to sea.

Society -- a group of individuals belonging to the same species and organized in a cooperative manner.

Soft corals -- colonial anthozoans with no hard skeleton.

Softwood -- the general term for the wood (secondary xylem) of conifers.

Somatic cell -- an ordinary body cell.

Sonar (sound navigation ranging) -- a technique or equipment used to locate objects underwater by the detection of echoes.

Spawning -- the release of gametes or eggs into the water.

Specialists -- a species that occupy a narrow range of habitats and eat a narrow range of foods.

Speciation -- the process by which two or more species are formed from a single ancestral stock.

Species -- a group of interbreeding individuals of common ancestry that are reproductively isolated from all other such groups.

Species-typical behavior -- the actions and displays that are broadly characteristic of a species.

Specific-Mate Recognition System (SMRS) -- signals that increase the likelihood that members of the same population will mate with one another.

Sperm -- the male sex cell.

Spermatophore -- a f ormed "container" or packet of sperm that is placed in or on the body of a female, in contrast to the sperm in copulation which are conducted directly from male reproductive structures into the female's body.

Sphincter -- a ringlike band of muscle fibers that constricts a passage or closes a natural orifice.

Spice -- a pungent, aromatic plant product derived from plants native to tropical regions and used to flavor foods.

Spine -- a sharp projection from the body or main part of a bone.

Spiracle -- an opening for ventilation. The opening(s) of the tracheal system of an arthropod or an opening posterior to the eye of a shark, skate, or ray.

Sponges -- an animal that consists of a complex aggregation of cells, including collar cells, and have a skeleton of fibers and/or spicules.

Spore -- a reproductive unit (often unicellular) that is capable of developing into a new organism without fusion with another cell.

Spout (blow) -- the water vapor and seawater that is observed when whales surface and exhale.

Spring overturn -- a springtime lake phenomenon that occurs when the surface ice melts and the surface water temperature warms to its greatest density at 4C and then sinks, creating a convection current that displaces nutrient-rich bottom waters.

Spring tides -- the tides with a large tidal range; they occur around the times of full or new moon.

Squatter towns -- a name given to shantytowns that occupy land without the landowner's permission.

Stalk-and-rush -- a form of hunting where predators approach prey as closely as possible, then close with a sudden burst of speed.

Stamen -- the floral organ that produces pollen; consisting of an anther and filament.

Standard Metropolitan Statistical Area (SMSA) -- an urbanized region with at least 100,000 inhabitants with strong economic and social ties to a central city of at least 50,000 people.

Starch -- a polysaccharide composed of a thousand or more glucose molecules; the chief food storage material of most plants.

Statutory law -- the rules passed by a state or national legislature.

Stenophagous -- an organism that eats very few kinds of foods.

Stereotyped behavior -- a pattern of behavior repeated with little variation in performance.

Sternum -- the ventral plate of an arthropod body segment or the breastbone of vertebrates.

Steroid -- an organic substance whose molecules include four complex rings of carbon and hydrogen atoms. Examples are estrogen, cholesterol, and testosterone.

Stewardship -- a philosophy that holds that humans have a unique responsibility to manage, care for, and improve nature.

Stimulant -- a psychoactive compound that excites and enhances mental alertness and physical activity.

Stimulus -- any form of energy an animal is able to detect with its receptors.

Stimulus filter -- the ability of the nervous system to block incoming stimuli that are unimportant for the animal.

Stipe -- a supporting stalk like those in mushrooms and brown algae.

Stock -- the size of a population.

Stomach -- the expansion of the alimentary canal between the esophagus and duodenum.

Stony corals -- Anthozoans, often colonial, that secrete a calcareous skeleton.

Stress -- the physical, chemical, or emotional factors that place a strain on an animal. Plants also experience physiological stress under adverse environmental conditions.

Stridulation -- the production of sound by an insect rubbing one body part against another (e.g., in male crickets).

Strike -- the deposition of fly eggs or larvae on a living host.

Strip-farming -- a method of farming where different kinds of crops are planted in alternating strips along land contours; when one crop is harvested, the other crop remains to protect the soil and prevent water from running straight down a hill.

Strip-mining -- the process of removing surface layers over coal seams using giant, earth-moving equipment.

Stromatolites -- massive calcareous skeletons formed by cyanobacteria (blue-green algae).

Succession -- the gradual replacement, through time, of one group of species in a community by other groups.

Succulent -- a fleshy plant that accumulates water.

Sucrose -- a disaccharide (glucose + fructose) found in many plants; the primary form in which sugar produced by photosynthesis is translocated.

Sudoriferous gland -- a sweat gland.

Sugar -- a monosaccharide; a carbohydrate with the general formula CnH2nOn.

Sulfide -- one of the minerals that is abundant in the hot water that seeps through hydrothermal vents.

Sulfur dioxide -- a colorless, corrosive gas damaging to both plants and animals.

Sulfur oxide -- produced from burning coal, this gas is a pollutant that can produce sulfuric acid in rain droplets.

Sun compass -- the mechanism in which animals use the sun and an internal clock that allows them to adjust for movement in the sun as they navigate.

Supply -- the quantity of a product being offered for sale at various prices.

Surf -- a wave that achieves enough height and steepness to break as it reaches a shoreline.

Surface current -- the long-term directional flow of water at the sea surface.

Suspension feeder -- the type of feeding whereby an animal obtains its nutrients by the removal of suspended food particles from the surrounding water by some sort of capturing, trapping, or filtering structure.

Sustainable agriculture -- an ecologically sound, economically viable, socially just, and humane agricultural system.

Sustainable development -- a real increase in well-being and standard of life for the average person that can be maintained over the long-term without degrading the environment or compromising the ability of future generations to meet their own needs.

Sustained yield -- the utilization of renewable resources at a rate that does not impair or damage the ability to be fully renewed on a long-term basis.

Swarming -- the aggregation of individuals for spawning or other purposes.

Sweeper tentacle -- a type of tentacle in corals that is used to sting neighboring colonies.

Swim bladder -- a gas-filled sac, which is usually located along the dorsal body wall of bony fishes; it is an outgrowth of the digestive tract and regulates buoyancy of a fish.

Symbiosis -- the living together of two different species in an intimate relationship. Symbiont always benefits; host may benefit, may be unaffected, or may be harmed (mutualism, commensalism, and parasitism).

Symmetry -- a balanced arrangement of similar parts on either side of a common point or axis.

Sympatric -- having the same or overlapping regions of geographical distribution.

Synapse -- the place at which a nerve impulse passes between neuron processes, typically from an axon of one nerve cell to a dendrite of another nerve cell.

Syndrome -- a group of symptoms characteristic of a particular disease or abnormality.

Syntax -- information provided by the sequence in which signals are transmitted.

System (organ system) -- a group of organs specialized for one function.

Systemic -- a condition or process that affects the whole body; many metabolic poisons are systemic.

Systole -- a phase of the cardiac cycle during which a heart chamber wall is contracted; also systolic pressure.

Systolic pressure -- the portion of blood pressure measurement that represents the highest pressure reached during ventricular ejection; it is the first number shown in a blood pressure reading.

T

T cell -- a t ype of lymphocyte with a vital regulatory role in immune response; so called because they are processed through the thymus.

Tactile -- pertaining to touch.

Tactile (touch) receptor -- a sensory receptor in the skin that detects light pressure.

Taiga -- areas of coniferous forests north of 50degree latitude having extended cold and snow cover winter conditions.

Tall grass prairie -- a grassland biome characterized by many tall grasses up to 5 meters tall.

Tannin -- a secondary product found in many plants that has been widely utilized as stains, dyes, inks, or tanning agents for leather; believed to function in plants by discouraging herbivores.

Tapeworms -- parasitic flatworms, typically consisting of a chain of repeated units.

Tarsal -- the ankle.

Taste buds -- the structures in the mouth and other locations that are sensitive to chemical stimuli.

Taxon -- a group of organisms that are genetically (evolutionarily) related.

Taxonomy -- the description of species and the classification of organisms into groups that reflect evolutionary relationships.

Teat -- the small protuberance at the tip of the breast of female mammals upon which the ducts of the mammary gland open to supply milk to the suckling young.

Technological optimists -- those who believe that technology and human enterprise will find cures for all our problems.

Technopolis -- a model of city development that proposes cities grow vertically instead of horizontally.

Tectonic estuary -- an estuary that results from the sinking of land due to movements of the crust.

Telophase -- the 4th stage of mitosis cell reproduction. The nuclear membrane and the nucleolus reappear and the cytoplasm undergoes constriction around the equator of the achromatic spindle. The constriction deepens and the original cell is gradually divided.

Temperate -- characterized by a mild or moderate temperature.

Temperate deciduous forest -- an ecosystem that occurs in regions with moderate climate and well-defined seasons dominated by deciduous trees.

Temperate rain forest -- a biome dominated by coniferous trees, high rainfall, and high humidity; moist coniferous forest.

Temporalis -- the human facial muscle which raises the mandible closing the mouth.

Tendon-- the connective tissue that joins muscle to bone in vertebrates.

Tensor -- a type of muscle which tightens or stretches a part of the body.

Tentacle -- a flexible, elongate appendage.

Terracing -- shaping the land to create level shelves of earth to hold water and soil enabling farmers to farm very steep hillsides.

Terrarium -- a closed biological system in which plants and animals coexist without external influences.

Terrestrial -- pertaining to the land.

Territoriality -- an intense form of competition in which organisms define an area surrounding their home site or nesting site and defend it, primarily against other members of their own species.

Territory -- the home or nesting site of an animal or family of animals guarded from other individuals of the same species.

Testes -- the sperm-cell producing organ found in males.

Testosterone -- male sex hormone secreted by the interstitial cells of the testes.

Tethys Sea -- shallow sea that once separated the Eurasian and African sections of the supercontinent Pangaea.

Tetrapods -- a non-taxonomic designation used to refer to amphibians, reptiles, birds, and mammals.

Thalamus -- the interior region of the brain where certain important sensory nerves, especially the optic nerve originate.

Thanatocoenose -- an assemblage of fossils that formed at the actual place of death.

Thermal plume -- plume of hot water discharged into a stream or lake by a heat source, such as a power plant.

Thermal pollution -- the pollution of heated water.

Thermal stratification -- the layering of different temperatures of water or air caused by different densities, less dense floating on more dense layers.

Thermocline -- a layer of water separating upper warmer and lighter water from lower colder and heavier water in a lake or sea; a stratum of abrupt change in water temperature.

Thermodynamics -- the study of energy transformations.

Thermoreceptor -- a sensory receptor that is sensitive to changes in temperature; a heat receptor.

Theropoda ("beast feet") -- a major grouping of dinosaurs that is comprised of carnivorous dinosaurs and birds.

Third World -- less-developed countries that are not capitalistic and industrialized ( First World ) or centrally-planned socialist economies ( Second World ); not intended to be derogatory.

Thoracic vertebrae -- the 12 vertebrae following the cervical vertebrae. They provide articulation for the ribs.

Thorax -- the Latin word for chest.

Thorn -- a modified stem terminating in a sharp point.

Thorn forest -- the dry end of a savanna community; hotter and drier than a typical savanna, these areas are characterized by dense, thorny small trees.

Threatened species -- a species that has declined significantly in total numbers and may be on the verge of extinction in certain regions or localities.

Threshold -- the minimum stimulus necessary to initiate an all-or-none response.

Thymus gland -- a ductless mass of flattened lymphoid tissue situated behind the top of the sternum; it forms antibodies in the newborn and is involved in the development of the immune system.

Thyroid gland -- an endocrine gland located in the neck of vertebrates that influences growth and development.

Tibia -- the medial and stronger of the two bones of the leg. It is prismoid in form, and possesses a shaft and two ends. Its purpose is to support the weight of the body.

Tidal bore -- a steep wave generated as high tides move up some estuaries and rivers.

Tidal current -- a current that is generated by tides.

Tidal energy -- energy that can be harnessed as a result of the movement of tides.

Tidal range -- the difference in water level between successive high and low tides.

Tide -- the periodic, rhythmic rise and fall of the sea surface.

Tide pool -- a depression that holds seawater at low tide.

Tide table -- a table that gives the predicted time and height of tides for particular points along a coast.

Timberline -- on mountains, the highest-altitude edge of forest that marks the beginning of the treeless alpine tundra.

Tissue -- a group of similar cells that performs a specialized function.

Tongue -- a muscular organ in the mouth of a tetrapod.

Tonsils -- a pair of small organs on either side of the root of the tongue composed of lymphatic tissue and instrumental in protecting the throat from infection.

Tool-making revolution -- the invention of tools, probably first of stone, wood, or bone, sometime in the early Paleolithic period. Knowledge of tool-making and tool-using technologies may have predated modern humans, as evidenced by tool utilization by other primates.

Topography -- the surface condition of an area of land; relief features.

Torpor -- a time of decreased metabolism and lowered body temperature that occurs in daily activity cycles.

Tortoiseshell -- the polished shell of hawksbill turtles.

Total fertility rate -- the number of children born to an average woman in a population during her entire reproductive life.

Total growth rate -- the net rate of population growth resulting from births, deaths, immigration, and emigration.

Toxic colonialism -- the habit of shipping toxic wastes to a weaker or poorer nation.

Toxins -- poisonous chemicals that react with specific cellular components to kill cells or to alter growth or development in undesirable ways; often harmful, even in dilute concentrations.

Trace element -- an element needed for normal metabolism but available only in minute amounts from the environment

Trace mineral -- dietary minerals that are required in minute quantities.

Trachea -- the windpipe. Also, any of the air tubes of insects.

Trade winds -- the steady winds that blow from east to west toward the Equator, replacing the hot air that rises at the Equator.

Tradition -- a behavior pattern that is passed from one generation to the next by learning.

Transitional zone -- a zone in which populations from two or more adjacent communities meet and overlap.

Translocation -- moving animals from one location to another.

Transpiration -- the evaporation of water from plant surfaces, especially through stomates.

Transplantation -- the movement of individuals or colonies from one location to another.

Trapezius -- a flat, triangular muscle, covering the back of the neck and shoulder.

Trauma -- an injury caused by accident or violence.

Trematoda -- the class of platyhelminthes that has members that are all parasitic; several holdfast devices present; have complicated life cycles involving both sexual and asexual reproduction.

Triceps -- muscles situated on the back of the upper armsin the human body.

Trichinosis -- a disease resulting from infection by Trichinella spiralis (Nematoda) larvae by eating undercooked meat; characterized by muscular pain, fever, edema, and other symptoms.

Trichome -- an epidermal appendage, such as a hair or scale.

Triglyceride -- a type of lipid formed from three fatty acids bonded to a molecule of glycerol; a fat or oil.

Trochanter -- a protuberance in the upper part of the femur to which the muscles attach.

Trochophore -- the early free-swimming, ciliated larval stage of many marine mollusks, annelid worms, ectoprocts, and brachiopods.

Trochophore larva -- a larval stage characteristic of many mollusks, annelids, and some other protostomate animals.

Trophic -- pertaining to feeding and nutrition.

Trophic levels -- the feeding level of an organism in an ecosystem; green plants and other autotrophs function at producer trophic levels; animals function at the consumer trophic levels.

Tropical rain forest -- an ecosystem characterized by very high rainfall and temperatures between 20 and 25C; very diverse life-forms; broad-leaved, non-deciduous trees; highly stratified forest.

Tropical seasonal forest -- semi-evergreen or partly deciduous forests tending toward open woodlands and grassy savannas dotted with scattered, drought-resistant tree species; distinct wet and dry seasons, hot year-round.

Tropics -- the equatorial regions with year-round warm weather.

Troposphere -- the layer of air nearest to the earth's surface; both temperature and pressure usually decrease with increasing altitude.

True language -- communication that includes the use of symbols to represent abstract objects or ideas, and syntax, where those symbols convey different messages depending on their sequence.

True navigation -- the ability to maintain or establish reference to a goal without the use of landmarks.

Tsetse fly -- a bloodsucking fly of the genus Glossina .

Tsunami -- a giant seismic sea swell that moves rapidly from the center of an earthquake; it can be 10 to 20 meters high when it reaches shorelines hundreds or even thousands of kilometers from its source.

Tube feet (podia) -- numerous small, muscular, fluid-filled tubes projecting from body of echinoderms; part of water-vascular system; used in locomotion, clinging, food handling, and respiration.

Tuber -- an enlarged, fleshy, underground stem tip, such as the potato.

Tubular eyes -- specialized eyes of many midwater animals that allow upward or downward vision.

Tumor -- a spherical mass of cells in which cell divisions occur at random and often in an uncontrolled fashion.

Tundra -- a terrestrial habitat zone located between taiga and Polar Regions ; characterized by absence of trees, short growing season, and mostly frozen soil during much of the year.

Tunicates (subphylum Urochordata) -- Chordates that show the three basic chordate characteristics only in the larva.

Turf -- the intertwined fibrous roots of grasses forming a mass with the soil just below ground level.

Turning over -- the mixing of thermal zones in a standing body of freshwater due to cold, more dense water "sinking" from the top through the other layers.

Turnover rate -- the rate at which members of a population or community replace themselves.

Tympanal organs -- the auditory receptors present on the abdomen or legs of some insects.

Tympanic (eardrum) -- relating to the tympanum that separates the outer and middle ear.

Tympanic bulla -- a bony case in the middle ear that encloses the sound-processing structures of mammals.

Tympanum ( middle ear) -- a cavity in the temporal bone filled with air, closed externally by the tympanic membrane and containing a chain of small bones which convey vibrations to the inner ear.

Type specimen -- a specimen deposited in a museum that formally defines the name of the species that it represents.

Typology -- a classification of organisms in which members of a taxon are perceived to share intrinsic, essential properties and variation among organisms is regarded as uninteresting and unimportant.

U

Ulcer -- area of inflammation that opens out to the skin or a mucous surface.

Ulna -- a Latin word meaning elbow.

Ulnar -- one of the two long bones which form the human lower arm. It connects with the humerus at the elbow.

Ultraviolet -- that portion of the sun's total range of radiation having wavelengths immediately shorter than the shortest of the visible spectrum (purple); between approximately 380 and 100 nm.

Umbilical cord -- cordlike structure that connects the fetus to the placenta.

Umwelt -- the sensory and perceptual world of the animal, dependent upon the types of sensory receptors that it possesses and the internal nervous system processes for receiving and interpreting those stimuli.

Undernourished -- those who receive less than 90 percent of the minimum dietary intake over a long-term time period.

Understory -- that vegetation which characterizes the lower level of plants in a forest; the vegetation below the canopy.

Ungulate -- any hoofed mammal.

Unicellular (cytoplasmic) organization -- the life-form in which all functions are carried out within the confines of a single plasma membrane; members of the kingdom Protista display unicellular organization; also called cytoplasmic organization.

Unsaturated fat -- a fat containing one or more double bonds between carbon atoms.

Upwelling -- convection currents within a body of water that carry nutrients from bottom sediments toward the surface.

Urban area -- an area in which a majority of the people are not directly dependent on natural resource-based occupations.

Urban renewal -- programs to revitalize old, blighted sections of inner cities.

Urbanization -- an increasing concentration of the population in cities and a transformation of land use to an urban pattern of organization.

Urea -- a nitrogen-containing waste product excreted in the urine of many vertebrates.

Ureter -- the tube which conveys urine from the kidney to the bladder.

Urethra -- the tube from the urinary bladder to the exterior in both sexes.

Uric acid -- the main nitrogenous excretory product in birds, reptiles, some invertebrates, and insects.

Uricotelic excretion -- having uric acid as the chief excretory product of nitrogen metabolism; occurs in reptiles and birds.

Urinary bladder -- the storage organ for urine.

Urochordata -- the subphylum of chordates whose members have all four chordate characteristics as larvae. Adults are sessile or planktonic and enclosed in tunic that usually contains cellulose. Sea squirts or tunicates.

Urogenital opening -- the common opening for urine and gametes in bony fishes and other animals.

Urophysis -- a discrete structure in the spinal cord of the fish tail that produces neuropeptides that help control water and ion balance, blood pressure, and smooth muscle contractions.

Uropod -- the posterior-most appendage of many crustaceans.

Uterine tube -- the tube that leads from the ovary to the uterus; also called fallopian tube.

Uterus (womb) -- the organ in female mammals, in which young are conceived, developed and are protected until birth.

Utilitarian conservation -- a philosophy that resources should be used for the greatest good for the greatest number for the longest time.

Utricle -- that part of the inner ear containing the receptors for dynamic body balance; the semicircular canals lead from and to the utricle.

V

Vaccine -- a preparation of either killed microorganisms; living, weakened microorganisms; or inactivated bacterial toxins (toxoids); administered to induce development of the immune response and protect the individual against a pathogen or toxin.

Vacuole -- a membrane-bounded, fluid-filled space in a cell.

Valve -- one of the two shells of a typical bivalve mollusk or brachiopod.

Variability -- generally refers to genetic differences between all organisms that result in uniqueness.

Variance -- a statistical measure of the amount of variation in a series of measurements.

Variation -- the difference or differences among individuals of a group or species that cannot be ascribed to age, sex, or position in the life cycle.

Vas -- Latin for duct or vessel.

Vascular plant -- a general name for any plant that has xylem and phloem.

Vascular system -- the total of the tissues that function in the conduction of water and food by means of xylem and phloem in the plant body.

Vascular tissue -- the tissue that is specialized for the long-distance transport of water or photosynthetic products; xylem and phloem.

Vegan -- a pure vegetarian consuming no animal products at all.

Vegetarian -- a person who does not consume animal flesh.

Vein -- 1. carries oxygen-depleted blood from the body to the heart in animals. 2 . a vascular bundle that forms part of the conducting and supporting tissue of a leaf.

Vena Cava -- the major vein returning blood to the heart of vertebrates.

Veneer -- a thin sheet of wood, often with attractive grain, used to cover less expensive wood.

Ventral -- the belly or towards the belly. In human anatomy, it refers to the anterior.

Ventricles -- chambers within the heart which force blood through the arteries.

Vertebra (pl. vertebrae) -- each of the bones that make up the backbone.

Vertebrata -- the subphylum of chordates whose members are characterized by cartilaginous or bony vertebrae surrounding a nerve cord. The skeleton is modified anteriorly into a skull for protection of the brain.

Vertebrates -- Chordates with a backbone.

Vertical migration -- the daily or seasonal movement of small marine animals between the photic zone and midwater depths.

Vertical stratification -- the vertical distribution of specific subcommunities within a community.

Vesicles -- membrane-bound particles pinched off by constriction of a membrane, as in the Golgi apparatus.

Vestige -- a rudimentary organ that may have been well developed in some ancestor or in the embryo.

Vestigial structures -- visible evidence of a structure that was present in an earlier stage in the evolution of an organism. One of the sources of evidence for evolution.

Viability -- the period of time an organism remains alive; often used to describe the length of time before a seed will fail to germinate.

Village -- a collection of rural households linked by culture, custom, and association with the land.

Virulence -- the degree of pathogenicity of an agent; how much damage the agent can cause.

Virus -- a submicroscopic noncellular particle composed of a nucleoprotein core and a protein shell; parasitic; will grow and reproduce in a host cell.

Viscera -- the internal organs in the body cavity.

Visceral mass -- the region of a mollusc's body that contains visceral organs.

Visible light -- a portion of the electromagnetic spectrum that includes the wavelengths used for photosynthesis.

Visible spectrum -- the portion of all the sun's radiation that can be perceived as light by humans; between approximately 380 and 750 nm in wavelength.

Vitamin -- an organic substance other than a carbohydrate, lipid, or protein that is needed for normal metabolism but cannot be synthesized in adequate amounts by the body.

Viviparous -- an animal whose eggs develop inside the female while the embryo derives nutrition from the mother.

Voluntary (somatic) nervous system -- the part of the nervous system that relays commands to skeletal muscles.

Vulnerable species -- naturally rare organisms or species whose numbers have been so reduced by human activities that they are susceptible to actions that could push them into threatened or endangered status.

W

Warning coloration -- a coloration pattern that allows organisms to escape from predators by advertising something harmful or distasteful.

Waste stream -- the steady flow of varied wastes, from domestic garbage and yard wastes to industrial, commercial, and construction refuse.

Water column -- the vertical column of seawater that extends from the surface to the bottom.

Water mass -- a body of water that can be identified by its temperature and salinity.

Water stress -- a shortage of water in plants resulting in decreased ability to function properly, because water affects all biochemical controls and is the medium for all chemical reactions.

Water vascular system -- a network of water-filled canals in echinoderms used in locomotion and food-gathering.

Water-vascular system -- a system of fluid-filled closed tubes and ducts peculiar to echinoderms; used to move tentacles and tube feet that serve variously for clinging, food handling, locomotion, and respiration.

Wave crest -- the highest part of a wave.

Wave shock -- the intensity of the impact of a wave.

Wave trough -- the lowest part of a wave.

Weather -- description of the physical conditions of the atmosphere (moisture, temperature, pressure, and wind).

Weed -- a plant not valued for its use or beauty and not intentionally planted; a category of hay fever plants that includes nongrass and nontree species.

Westerlies -- the winds that blow from west to east at middle latitudes.

Wetlands -- ecosystems of several types in which rooted vegetation is surrounded by standing water during part of the year.

White blood cell (leukocyte) -- a type of blood cell involved with body defenses.

Whorled -- three or more leaves attached at a node.

Wilderness -- an area of undeveloped land affected primarily by the forces of nature; an area where humans are visitors who do not remain.

Wildlife -- plants, animals, and microbes that live independently of humans; plants, animals, and microbes that are not domesticated.

Wildlife refuges -- areas set aside to shelter, feed, and protect wildlife; due to political and economic pressures, refuges often allow hunting, trapping, mineral exploitation, and other activities that threaten wildlife.

Wind farms -- large numbers of windmills concentrated in a single area; usually owned by a utility or large-scale energy producer.

Windbreak -- rows of trees or shrubs planted to block wind flow, reduce soil erosion, and protect sensitive crops from high winds.

Windward -- the side toward which the wind is blowing.

Winter sleep -- a period of inactivity in which a mammal's body temperature remains near normal and the mammal is easily aroused.

Withdrawal -- a description of the total amount of water taken from a lake, river, or aquifer.

Wood -- secondary xylem.

Wood pulp -- a watery suspension of pulverized wood used in the production of paper, cardboard, fiberboard, rayon, cellophane, and other products.

Woodland -- a forest where tree crowns cover less than 20 percent of the ground; also called open canopy.

World conservation strategy -- a system of maintaining essential ecological processes, preserving genetic diversity, and ensuring that utilization of species and ecosystems is sustainable.

World Ocean -- the interconnected world seas and oceans.

X

X ray -- very short wavelength in the electromagnetic spectrum; can penetrate soft tissue; although it is useful in medical diagnosis, it also damages tissue and causes mutations.

Xanthophyll -- a group of yellow or golden photosynthetic pigments.

Xeric -- characterized by a very dry environment.

Xerophyte -- a plant adapted for growth under arid conditions.

X-ray crystallography -- a technique for studying molecular and atomic structure of a substance.

Xylem -- in vascular plants, the tissue that conducts water and minerals.

Y

Yeasts -- one of several species of ascomycete fungi in which an extensive mycelium is not produced, so that the organism is usually unicellular.

Yellow fever -- virus disease transmitted by the mosquito Aedes aegypti .

Yolk -- part of an embryo which serves as nutrition for the rest of the embryo.

Yolk sac -- the stored food reserve (yolk) and its surrounding membranes, which is found in embryonic reptiles, birds, and mammals.

Z

Zeitgeber -- any entraining agent that plays a role in setting or resetting an internal biological clock. Examples include sunrise or sunset.

Zero population growth (ZPG) -- the number of births at which people are just replacing themselves; also called the replacement level of fertility.

Zoea -- an early larval stage of many crustaceans.

Zoid -- a member of a colonial organism.

Zooflagellates -- the members of the Zoomastigophora, the animal-like flagellates (phylum Sarcomastigophora).

Zoology -- the study of animals.

Zoonosis -- disease of animals that is transmissible to humans.

Zooplankton -- the animal component of the plankton, having only limited locomotory powers.

Zygomatic bone -- the bone in the skull responsible for the prominence of the upper and anterior part of the cheek. It forms the lateral part of the lower margin of the orbital opening.

Zygote --  a diploid cell produced by the fusion of an egg and sperm; fertilized egg cell.