B Cell

A lymphocyte that produces antibodies in response to antigens.


A rod-shaped bacterium.

Background extinction rate

Normal rate of extinction -- as a natural part of the evolutionary process -- of various species as a result of changes in local environmental conditions and the actions of natural evolutionary forces. Extinctions not caused or contributed to by the actions of humans.


Microorganisms that break down organic materials in the first stages of composting. It is bacteria that generate the heat associated with hot composting. The three types of bacteria are psychrophilic, mesophyllic, and thermophilic.


A virus that infects bacteria.


One of the keratinous plates that function to filter food from water in some whales.


A branch of a vane in the feather of a bird.


A branch of a barb in the feather of a bird.


Any substance that increases the concentration of hydroxide (OH – ) ions when added to a water solution.

Base Unit

One of seven fundamental units of SI measurement that describe length, mass, time, and other quantities.

Base-Pairing Rule

The rule stating that in DNA, cytosine pairs with guanine and adenine pairs with thymine and in RNA, adenine pairs with uracil.


The fruiting body of a basidiomycete.


A specialized club-shaped reproductive structure that forms on the gills of mushrooms.


To flutter off the fist or perch; an abortive attempt to fly when the bird is restrained by the leash.

Benign Tumor

An abnormal but nonthreatening cell mass.

Benthic Zone

The ocean bottom.


A plant having a two-year life cycle.

Bilateral Symmetry

In animals, a body plan in which the left and right sides mirror each other.


A yellowish fluid secreted by the liver that functions as a fat emulsifier in digestion.

Binary Fission

An asexual cell division of prokaryotes that produces identical offspring.


To grab and hold onto quarry (or volunteers) with the feet.

Binomial Nomenclature

A system of naming organisms that uses the genus name and a species identifier.

Binomial nomenclatureThe two-name system, developed by Carolus Linnaeus (the founder of modern taxonomy), used to assign scientific names to all living things. Homo sapiens, for example, is the scientific name for humans. The first name is the genus name and is always capitalized. This is sort of like your last name... it belongs to several of your close relatives, too, and it shows that you are all closely related. The second name is the species name is always lower case. This is like your first name, which no one else in your circle of relatives posseses and so it uniquely identifies you. Memory tool: you probably know the meanings of the terms generic (i.e. general, broad) and specific (i.e. precise, exact). These terms come from the same origins as genus and species, so recalling their meaning will help you recall the relationship between the two portions of a scientific name.


The absorption of toxic chemicals in plants and animals; some time referred to as bioconcentration.

Biochemical Pathway

A series of chemical reactions in which the product of one reaction is consumed in the next reaction.

Biochemical Pathway

A series of chemical reactions in which the product of one reaction is consumed in the next reaction.


An agent that kills many organisms in the environment.


Able to be broken into simpler chemical compounds by microorganisms. Organic materials are biodegradable.

Biodegradable material

Materials that can be broken down by micro organisms into simple stable compounds such as carbon dioxide and water. Most organic material such as food scraps and paper are biodegradable


 Biodegradation or biotic degradation or biotic decomposition is the chemical dissolution of materials by bacteria or other biological means. The term is often used in relation to ecology, waste management, biomedicine, and the natural environment and is now commonly associated with environmentally friendly products that are capable of decomposing back into natural elements.


Biodiesel is registered with the Environmental Protection Agency as a pure fuel or as a fuel additive and is a legal fuel in commerce. It is typically produced through the reaction of a vegetable oil or animal fat with methanol in the presence of a catalyst to yield glycerin and biodiesel (chemically called methyl esters). It is an alternative fuel that can be used by itself or blended with petroleum diesel for use in diesel engines. Its use can result in substantial reduction of unburned hydrocarbons, carbon monoxide, and particulate matter.


It refers to the variety and the variability among living organisms. These include diversity within species, between species, ecosystems etc.


The theory that living organisms come only from other living

Biogeochemical CycleThe process by which materials necessary for organisms are circulated through the environment.


Study of the geographical distribution of fossils and living organisms.

BiogeographyA branch of geography that deals with the geographical distribution of animals and plants.


Biological control

Controlling plants’ diseases, and animal pests using natural enemies; or inhibiting the reproduction of pests by methods that result in the laying of infertile eggs, etc. Bio-control method may be an alternative or compliment to chemical pest control methods.

Biological resources

Includes genetic resources, organisms or parts thereof, populations, or any other biotic component of ecosystems with actual or potential use or value for humanity.

Biological Species Concept

The principle that defines a species as those organisms that can produce offspring together.

Biologically unique species

A species that is the only representative of an entire genus or family.


The production of light by means of a chemical reaction in an organism.

BiomagnificationThe accumulation/magnification of a substance as it moves through the food.

BiomassThe dry weight of organic material in an ecosystem.


A geographic area characterized by specific kinds of plants and animals.


A major portion of the living environment of a particular region (such as a fir forest or grassland), characterized by its distinctive vegetation and maintained largely by local climatic conditions.


A pesticide that is biological in origin (i.e., viruses, bacteria, pheromones, natural plant compounds) in contrast to synthetic chemicals. Transgenic Bt cotton and corn are biopesticides because Bacillus thuringiensis (Bt) is a naturally occurring soil bacterium that has been genetically engineered into the plants.

Bioregion (bioregional planning)

A territory defined by a combination of biological, social, and geographic criteria, rather than geopolitical considerations; generally, a system of related, interconnected ecosystems.


The portion of the earth and its atmosphere in which living organisms exist or that is capable of supporting life.


The area on and around Earth where life exists.


The area on and around Earth where life exists.

Biosphere reservesBiosphere reserves are a series of protected areas linked through a global network, intended to demonstrate the relationship between conservation and development, established under UNESCO's Man and the Biosphere (MAB) Program.


The living organisms of a region.


Pertaining to any aspect of life, especially to characteristics of entire populations or ecosystems.

Biotic Factor

A living component of an ecosystem.


The ability to walk upright on two legs.


The larva of echinoderms.

Birth Rate

The number of births occurring in a period of time.


An aquatic mollusk with a shell divided into two halves connected by a hinge, such as a clam, oyster, or scallop.


The broad, flat portion of a typical leaf.


The central cavity of a blastula.


A depression formed when cells of the blastula move inward.


A hollow ball of cells formed when a zygote undergoes repeated cycles of cell division.


A disease of plants characterized by quickly developing decay and discoloring of leaves, stems, and flowers.

Blood Alcohol Concentration (BAC)

A measurement of the amount of alcohol in a person’s blood.

Blood Pressure

The force that blood exerts against the walls of a blood vessel.

Blood Type

A specific characteristic of the blood of an individual; A, B, AB, or O, depending on the type of antigen present on the surface of the red blood cell.


The rapid lengthening of internodes caused by gibberellic acid.

Bone Marrow

The soft tissue in the center and ends of long bones where blood cells are produced.

Book Lung

In the abdomen of an arachnid, an organ for gas exchange with parallel folds that resembles the pages of a book.

Botanical pesticides

Pesticides whose active ingredients are plant-produced chemicals such as nicotine, rotenone, or strychnine. Also called plant-derived pesticides.Being "natural" pesticides, as distinct from synthetic ones, they are typically acceptable to organic farmers.


The scientific study of plants.

Bowman’s Capsule

Cup-shaped structure of the nephron of a kidney which encloses the glomerulus and in which filtration takes place.

Brain Stem

The region of the brain that lies posterior to the cerebrum and that connects the cerebrum to the spinal cord.



A group of animals descended from common ancestors and possessing similar characteristics.

BreedA group of animals or plants related by descent from common ancestors and visibly similar in most characteristics. Taxonomically, a species can have numerous breeds.



A male or female kept for reproduction.

Breeding line

Genetic lines of particular significance to plant or animal breeders that provide the basis for modern varieties.


A small tube that branches from the bronchi within the lungs.


One of the two branches of the trachea that enter the lungs.


A plant that has no vascular tissue and does not form true roots, stems, and leaves.


A structure that develops on the stem at the point of attachment of each leaf.

Bud Scale

A modified leaf that forms a protective covering for a bud until it opens.


In fungi, a form of asexual reproduction in which a part of a cell pinches off to produce an offspring cell.


Chemical that neutralizes small amounts of acids or bases added to a solution.

Buffer zone

The region near the border of a protected area; a transition zone between areas managed for different objectives.

Buffer zones

Areas on the edge of protected areas that have land use controls and allow only activities compatible with protection of the core area, such as research, environmental education, recreation, and tourism.