A posterior segment of an animal that usually houses the organs of
digestion and excretion.


Nonliving or not containing any living organisms.

Abiotic factors

Environmental influences produced other than by living organisms; for example, temperature, wind patterns, humidity, pH, substrate rock type, and other physical and chemical influences.

AbomasumThe final compartment of the ruminant stomach, also known as the fourth or true stomach of the cow, comparable in function to the simple-stomached animals.


Aboral surface

The surface opposite the mouth on an echinoderm.

Abscisic acid

A hormone in plants that helps regulate the growth of buds and
the germination of seeds.

Abscission zone

The area at the base of a leaf petiole where the leaf breaks off
from the stem.


In digestion, the movement of nutrients to the circulatory system.

Accessory pigment

A pigment that absorbs light energy and transfers energy to
chlorophyll a in photosynthesis.


The latin name for a genus of raptors, the short winged hawks of classic falconry, such as goshawks or cooper's.


The process of an organism’s adjustment to an abiotic factor.



adjustment to altered environmental conditions.

Acid fallout

Molecules of acid formed from reactions high in the atmosphere involving nitrogen, sulfur oxides, and water vapor that settle out of the atmosphere without any additional water.

Acid rain

The precipitation of sulfuric acid and other acids as rain. The acids form when sulfur dioxide and nitrogen oxides released during the combustion of fossil fuels combine with water and oxygen in the atmosphere.


An inflammatory disorder of the sebaceous glands characterized by skin
lesions in the form of pimples, blackheads, and sometimes cysts.


An animal with no coelom, or body cavity.


The volume of water that would cover one acre of land to a depth of one foot. An acre foot is the basic measure of agricultural water use.


One of the two protein filaments in a muscle cell that function in


A member of a class of bacteria characterized as rod-shaped monerans that form branched filaments.

Activation Energy

Amount of energy required for a chemical reaction to start
and to continue on its own.

Active Transport

The movement of a substance across a cell membrane against a
concentration gradient; requires the cell to expend energy.


An antiviral drug.


An inherited trait that increases an organism’s chance of survival in a particular environment.

Adaptive Radiation

An evolutionary pattern in which many species evolve from
a single ancestral species.


A nitrogen-containing base that is a component of a nucleotide.

Adenosine Diphosphate (ADP)

A substance involved in energy metabolism formed by the breakdown of adenosine triphosphate.

Adenosine Triphosphate (ATP)

A molecule present in all living cells and acting as an energy source for metabolic processes.


The attractive force between unlike substances.



Adrenal Gland

An endocrine gland located on the top of a kidney.

Adrenaline Epinephrine

A hormone secreted by the adrenal medulla that raises
the level of glucose in the blood, increases the heartbeat, and raises blood

Adrenocorticotropic Hormone

A hormone that stimulates the adrenal cortex.


An organism that utilizes atmospheric oxygen in its metabolic pathways.

Aerobic Respiration

The process in which cells make ATP by breaking down
organic compounds, with oxygen as the final electron acceptor.

Afferent Neuron

A neuron that conducts impulses toward the central nervous system.

AflatoxinToxin produced by the fungi Aspergillus flavus and Aspergillus parasiticus.



A crop damaging carcinogen that is produced by mold in stored crops. It is prominent in crops that are stored while still moist.


The remains of the placenta and the amnion, expelled from the mother’s body following birth.


A gel-like base for culturing microbes; extracted from the cell walls of red algae.

Age Structure

The distribution of individuals among different ages in a population.

Agenda 21

The international policy agreed on at the Rio Conference in 1992. Under Agenda 21, countries agreed to work towards sustainable social, economic and environmental development.


The combination of the producing operations of a farm, the manufacture and distribution of farm equipment and supplies and the processing, storage, and distribution of farm commodities.

Agricultural Diversification

Agricultural diversification refers to a shift from one particular cropping system to a varied and multi-cropping system to stabilized farm income (particularlyon small farm holdings) and protects our natural resources.

Agricultural Pollution

Wastes, emissions, and discharges arising from farming activities. Causes include runoff and leaching of pesticides and fertilizers; pesticide drift and volatilization; erosion and dust from cultivation; and improper disposal of animal manure and carcasses.


The art and science of producing crops, raising livestock and their preparation and marketing for use by the human beings.

Agriculture Economy

An economic system based primarily on crop production.

Agriculture Land

Agricultural land is land including arable land, land under permanent crops and land under permanent meadows and pastures.

Agriculture Prices

It is the exchange value of agricultural commodity, determined by buyers and sellers in the market and is expressed in terms of money.


Production of tree crops in a manner similar to agriculture. Also production of trees along with regular crops.

AgronomicAn adjective used to describe plants and plant products. Pertains to agronomy or agricultural plants and things affecting plants.



The science of crop production and soil management.

AI = artificial inseminationThe technique that involves breeding of females without the males being physically present.

Alcoholic Fermentation

The process by which pyruvic acid is converted to ethyl alcohol; the anaerobic action of yeast on sugars.


The disease of addiction to ethanol.


A hormone that helps maintain water and salt balance.


Autotrophic protists.

Alien species

A species occurring in an area outside of its historically known natural range as a result of intentional or accidental dispersal by human activities (also known as an exotic or introduced species).


In amniotic eggs, the membranous sac that contains many blood vessels; in humans, a membrane surrounding the embryo that becomes the umbilical cord.


An alternative form of a gene.

Allele Frequency

The percentage of an allele in a gene pool.


A usually harmless antigen in the environment that is capable of
inducing an allergic reaction.


Immune reaction to an allergen.

All-in all-out systemsA livestock management system in which all animals are introduced into an isolated confinement unit, taken through the appropriate stage of the production cycle and all moved out at the same time. The unit is then cleaned thoroughly and disinfected before a new group comes in.

Alternative Agriculture

Agriculture based on reduced use of chemical fertilizers and pesticides, increased use of crop rotation, enhance sustainability, improve efficiency and profitability and reduce tillage of soil.

Alternative Crops

Non-traditional crops that can be in an area to diversity rotations, and increase income.


Referring to birds that, at hatching, are immature and in need of parental

Altruistic Behavior

Sacrifice by one individual that results in a benefit for
another individual.


One of the tiny air sacs found in the lungs.

ambient air


The air immediately around us.

Amebic Dysentery

A sometimes fatal disease caused by an amoeba that enters the body in contaminated food or water.


In sponges, an amoebalike cell that moves through the body cells, supplying nutrients, removing wastes, and transporting sperm during sexual reproduction.

Amino Acid

A carboxylic acid with an amino group; one of 20 monomers that form proteins.

Amino Acid–Based Hormones

Agroup of hormones that includes proteins, peptides, amino acids, and other forms derived from amino acids.


In the nitrogen cycle, the formation of ammonia compounds.


A procedure used in fetal diagnosis in which fetal cells are removed from the amniotic fluid.


A bulblike sac at the base of the tube foot of an echinoderm that functions in movement.

AnaerobeAn organism capable of living in the absence of free oxygen.

Anal Pore

In protozoa, an opening from which wastes are eliminated.

Analogous Structure

In evolution, structures in more than one organism that have similar appearance and function, but different embryological origin.


A phase of mitosis and meiosis in which the chromosomes separate.

Anatomy Anatomy is the study of the structure of organisms.



A hormone secreted by the testes that controls secondary sex characteristics.


A flowering plant.


A bilaterally symmetrical, segmented worm, such as an earthworm or a leech.


Any plant which completes its entire life cycles and dies within one year or less.

Annual Ring

A yearly growth ring in a woody plant.


The front end of a bilaterally symmetrical organism.


The microsporangium of an angiosperm in which pollen grains are produced.


In plants, algae, and fungi a reproductive structure that produces gametes by mitosis.



The belief that humans hold a special place in nature, being centered primarily on humans and human affairs.


Anthropoid Primate

One of a subgroup of primates that includes monkeys and apes.


A chemical that can inhibit the growth of some bacteria.


A protein produced by B cells that binds to antigens.


A region of tRNA consisting of three bases complementary to the codon of mRNA.

Antidiuretic Hormone

A hormone that helps regulate solute concentration in the blood.


A substance that stimulates an immune response.


The largest artery in the human body; carries blood from the left ventricle to systemic circulation.

Aortic Valve

The semilunar valve on the left side of the heart.

Aphotic Zone

The ocean layer that receives no light.

Apical Dominance

A plant growth pattern in which branches near the shoot tip are shorter than branches farther from the shoot tip.

Apical Meristem

The growing region at the tips of stems and roots in plants.


Any complex part or organ extending from the body.

Appendicular Skeleton

In vertebrates, the bones that form the limbs.


An underground geological formation, or group of formations, containing usable amounts of groundwater that can supply wells or springs for domestic, industrial, and irrigation uses.

Aquifer Depletion

Depletion of water of an aquifer resulting from withdrawal that is greater than natural or artificial recharge.

Arable land

Land that can be cultivated


An arthropod with four pairs of walking legs; a spider, scorpion, mite, or tick.

Arachnoid Membrane

The middle layer of the three sacs that surround the brain and spinal cord.


A prokaryotic organism distinguished from other prokaryotes by the composition of the cell membranes and walls.


In seedless plants, a reproductive structure that produces a single egg by mitosis.

Arid Climate

A dry climate with an annual precipitation usually less than 10 inches and the level of evaporation is greater than the level of precipitation. It is not suitable for crop production without irrigation.


A branch of an artery that gives rise to capillaries.


A vessel that carries blood away from the heart to the body’s organs.

Arthropod Segmented

Animal with jointed appendages and an exoskeleton.

Artificial Fertilizer

A chemical added to soil to enhance crop production.

Artificial Selection

Breeding of organisms by humans for specific phenotypic characteristics.


The fruiting body of an ascomycete.


A gamete-producing structure in ascomycetes.


One of eight haploid cells in an ascus.


A spore sac that forms on the surface of an ascocarp.

Asexual reproduction

A method of reproduction in which genetically identical offspring are produced from a single parent; occurs by many mechanisms, including fission, budding, and fragmentation.



Asexual Reproduction

The production of offspring that does not involve the union of gametes.


An integrated group of species inhabiting a given area; the organisms within a community influence one another's distribution, abundance, and evolution. (A Human Community is a social group of any size whose members reside in a specific locality.)

Asteroid-Impact Hypothesis

The hypothesis that the extinction of the dinosaurs was caused by the impact of a huge asteroid.


A chronic respiratory condition characterized by recurring attacks of wheezing, coughing, and labored breathing.


A disease characterized by the buildup of fatty materials on the interior walls of the arteries.


The mass of air surrounding the Earth.


The simplest particle of an element that retains all the properties of that element.

Atomic Number

The number of protons in an atom.

ATP Synthase

An enzyme that catalyzes the synthesis of ATP from ADP and phosphate.

Atrioventricular Node

A group of nerves in the heart that functions in the heartbeat.

Atrioventricular Valve

A one-way valve separating each atrium from the ventricle beneath it.


An anterior chamber of the heart.

Attenuated Strain

Refers to a preparation of a virus for a vaccine in which the virus is incapable of causing disease under normal circumstances.

Auditory Canal

The tube through which air enters the ear.


Early hominid from the genus australopithecus.

Autoimmune Disease

A disorder in which the immune system attacks the organism’s own cells.

Autonomic Nervous System

A division of the peripheral nervous system that controls the involuntary actions that regulate the body’s internal environment.


A chromosome that is not a sex chromosome.


The ability of an organism to deliberately drop a body part, most often to escape a predator.


An organism that uses energy to synthesize organic molecules from inorganic substances.


Literally, "self eater." Organisms capable of producing their own food.


A plant hormone that regulates cell elongation.


The class of animals that exclusively includes birds

Axial Skeleton

The backbone, skull, and associated bones of vertebrates.


In a neuron, an elongated extension that carries impulses away from the cell body.

Azidothymidine (AZT)

An antiviral drug that inhibits the reverse transcriptase of retroviruses, such as HIV.