From acid rain to zoonotic disease, we will help you understand key terms and concepts behind the science and health topics covered on this website. Some of these terms and concepts are so new, you won't even find them in a dictionary. But concise definitions—written especially for students and teachers—are never more than a click away.

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

A

Acid rain—Rain containing droplets of nitric acid and sulfuric acid, formed when water molecules combine with gases such as sulfur dioxide (SO2) or nitrogen oxides (NOx)in the atmosphere and fall to Earth. Is especially harmful to fish and other aquatic life in rivers and lakes.

Acidic—Condition of water, soil, or a solution containing excess hydrogen atoms producing a pH of less than 7; the opposite of alkaline. Sour or sharp-tasting liquids such as lemonade, orange juice, and vinegar are acidic. If soil or water is too acidic, plants cannot grow.

Acre-foot—The amount of water needed to flood an acre of land to a depth of one foot. Acre-inch is one-twelfth of an acre foot.

Acquired immunity (adaptive immunity)—The body's protective mechanism that is induced through vaccination or being exposed to a disease. Acquired immune responses are targeted to specific microbes, such as those that cause measles and smallpox.

Acute pesticide poisoning—A toxic condition, usually a result of inhaling or swallowing a pesticide, and characterized by a rapid onset of severe symptoms. Can be fatal.

Adapt—To change to fit a new situation or set of circumstances, as humans, for instance, have adapted to different climates around the globe or as certain bacteria have adapted to antibiotics and become resistant to them.

Aerosol—A small droplet or particle suspended in the atmosphere. Aerosols are released into the atmosphere naturally in sea spray and volcanic ash and as the result of human activities such as burning fossil fuels. The term also refers to a product that relies on a pressurized gas to propel a substance out of a container, such as spray paint or hairspray.

Agent Orange—A toxic herbicide and defoliant used by the U.S. during the Vietnam War to clear dense jungle foliage in which enemy forces hid. The name comes from the orange stripe on the barrels that stored the chemical.

AIDS highways—Name given by journalists to certain trucking routes in India and Africa along which HIV/AIDS spreads.

Airport malaria—Name given to malaria cases in people who live near airports in countries that have no malaria. Malaria-bearing mosquitoes are believed to arrive by airplane.

Air quality alert—Government warning issued when air emissions—substances discharged into the air by motor vehicle engines and other sources—contain pollutants that are at potentially harmful levels. Alerts are based on the air quality index.

Air quality index—A way to measure the amount of the six major pollutants in the air. These pollutants are particulates, sulfur dioxide (SO2), carbon monoxide (CO), nitrogen dioxide (NO2), lead (Pb), and ozone (O3). A measurement of 0 to 100 is considered acceptable, but from 100 to 150 is unhealthy for old people, young children, and people with asthma. Above 150 is unhealthy for everyone.

Akkadians—A Semitic-speaking group of people who lived, circa 2300 BC, in the region known today as the Middle East and who had the world's first large empire.

Algae—Single-celled organisms that live in both fresh and salt water and contain chlorophyll, the substance plants use to make food from sunlight. Algae is the plural; alga is the singular.

Algicides—Synthetic or natural chemical compounds used to kill or control unwanted algae (‘cide’ means killer).

Alkalinity—The capacity of water to neutralize or buffer acids. A solution is alkaline when its pH value is above 7. High levels in water or soil can lead to problems.

Allergy—A major defense mounted by the body's immune system against normally harmless substances, or allergens, such as chemicals in pollen, food, bee stings, animal dander, or dust. An allergic reaction is the body's strong reaction to these substances in a person who is sensitive to them. Reactions range from mild to severe, and may include sneezing, a rash, or difficulty breathing (which can be fatal). Allergens trigger allergic reactions in people with allergies.

Amino acids—Small chemical compounds that are the building blocks used to construct proteins. They are also the end product of protein digestion. The body uses 20 amino acids to build all of its proteins. Nine of these are called essential amino acids. Because they are not manufactured by the body, it is essential that we get them from our diet.

Anemia—A condition in which the body lacks enough red blood cells to carry necessary oxygen. It can result from an inadequate or unhealthy diet and can be life-threatening.

Antarctica—The continent centered around the South Pole. Antarctica is a plateau covered by mountains and ice, with 95% of its surface under an icecap averaging one mile in thickness.

Anthrax—A disease that exists primarily in cows and other animals that live in herds. The bacterium Bacillus anthracis causes the disease, which can leap to humans who come into contact with infected animals or the products made from them. Anthrax can be fatal in humans when it affects the lungs or digestive system.

Antibiotic—A chemical usually made by a living organism that kills bacteria and other microbes that cause disease.

Antibiotic resistance—Occurs when bacteria or other microbes that cause disease evolve into forms that can no longer be killed by antibiotics. It is the reason people are not given antibiotics as readily as in the past.

Antibodies—Complex proteins in the blood that the body produces in response to specific bacteria, viruses, parasites, and other antigens. Humans and other vertebrates have acquired immune systems that use antibodies to fight disease.

Antigens—Substances that when introduced into the body, stimulate the production of antibodies. Antigens include toxins, bacteria, foreign blood cells, viruses, and cells of transplanted organs. The word "antigen" comes from antibody generation.

Antioxidants—Compounds that neutralize oxidants (free radicals) that are produced when cells in the body burn oxygen to produce energy. Oxidants can clog arteries and contribute to cancer, diabetes, and other diseases. Antioxidants, found in fruits and vegetables, contribute to good health.

Apollo 12—The second manned spaceship to land on the moon, launched November 14, 1969.

Aquaculture—Raising fish, shrimp, oysters, and other marine or freshwater foods under controlled conditions in water, either in ponds on shore or contained in net cages located in bays or in the open ocean. Also called mariculture.

Aqueducts—Water pipes, channels, or troughs that carry water, usually by gravity. Sometimes cut through rock and out of view, the most famous aqueducts were built of rock by the ancient Romans and towered above the landscape.

Aquifer—Underground layers of rock, sand, gravel, or sediment that trap, store, and transport water. It generally holds enough water to be used as a water supply.

Aquifer depletion—Using the water in an aquifer faster than nature can replace it.

Arachnids—A type of arthropod that lives on land, has eight legs, and usually eats other animals. This group includes spiders, scorpions, and daddy longlegs.

Arid—Land or climate that is extremely dry because it has very little rain or snow. Agriculture is impractical in such places without irrigation.

Arsenic—A naturally occurring element that is often used in pesticides and herbicides. It can bioaccumulate to toxic levels, and is known to cause cancer in humans and other living things.

Arthropods—Invertebrate animals with skeletons on the outside, segmented bodies, and jointed legs. This group includes all insects, crustaceans, and spiders.

Aspirin—A human-made, synthetic version of salicylic acid, used to reduce fever and inflammation and relieve pain. Originally sold as a powder, and now in tablets, aspirin was a trademarked name until 1921. Researchers keep finding new ways that aspirin promotes and protects human health.

Asthma—A respiratory condition that accounts for 10 million absences from school in the U.S. each year. A person who has asthma has trouble breathing, often feels a sense of constriction in the chest, and gets attacks of coughing or gasping.

Atmosphere—The mixture of gases surrounding the Earth. It is made up of nearly 79% nitrogen, 21% oxygen, and small amounts of carbon dioxide and other gases. The atmosphere is divided into four layers, from the closest to the Earth to the farthest: troposphere, stratosphere, mesosphere, and thermosphere.

Atoms—The basic units that make up all chemical elements and matter. Atoms, in turn, are made up of a central nucleus, containing protons and neutrons, surrounded by electrons. To see and learn more, go to NASA's Glimpse into the Mysteries of the Universe page.

Avian flu ("bird flu")—An infection caused by bird (avian) flu viruses. These viruses occur naturally in wild birds, which usually do not get sick. Chickens, turkey, ducks, and other domesticated birds can become very ill and die. Humans can pick up avian flu from contact with the droppings, saliva, or blood of infected birds. Symptoms range from fever and cough to pneumonia, depending on the virus causing the infection. Though difficult to catch, it is deadly. Over half the humans who have caught it have died. Currently, humans cannot infect other humans, but if the virus mutates and makes that possible, a serious pandemic could occur.

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B

Bacteria—One-celled organisms that exist almost everywhere. Countless numbers live in the human body. Some cause diseases such as cholera and strep throat. Others provide useful functions, such as those that live in soil and break down dead organic matter into nutrients used by plants. Bacteria is the plural; bacterium is the singular.

Bedrock—The solid rock that underlies loose material, such as soil, sand, clay, or gravel.

Bioaccumulates—Substances taken into the body through contaminated food, water, or air that build up slowly in body tissues or fat because they are slow to break down or be excreted. Noun: bioaccumulation.

Bioactive—Having the ability to interact with a living tissue or system, such as a human being or other living organism.

Bioconfinement—Efforts to keep the pollen in genetically engineered (GE) plants from escaping (carried by wind or insects) and mating with non-GE-plants.

Biodiversity—One word made from the two words biological and diversity, referring to the many types of plants and animals that live in a region. The more species, the greater the biodiversity.

Bioengineered—Process of having been genetically altered by an emerging new science called biotechnology, in order to introduce new traits to the species.

Biopharming—To genetically engineer a plant or animal to produce a pharmaceutical (or medicinal) drug, vaccine or industrial substance. Such experimental practices create public concern.

Biotechnology—A scientific process by which living things (usually plants or animals) are genetically engineered.

Bioterrorist—A person who uses biological weapons (bioweapons) for political gain. These "weapons" may include fungi, viruses (such as smallpox or Ebola), or bacteria (such as anthrax).

Bioweapons—Weapons that use pathogens or disease-causing agents, such as bacteria, viruses, or fungi.

Blood flukes—The trematode worms that cause schistosomiasis. The larval forms of these parasites live in lakes and irrigation ditches with snails (essential to the parasite's life cycle). When people swim or bathe in the water, the worms burrow through their skin and into their bloodstream. The worms then lay eggs in their bodies and make them ill.

Bloom—To grow or flourish, as algae do at or near the water's surface (verb). An algae bloom is a visible, colored area on the surface of a body of water caused by excessive growth (noun).

Brackish—Water with mild salinity, usually occurring where a river (fresh water) empties into an ocean (salt water). Brackish water environments are fluctuating environments.

Bromine—An element (chemical symbol Br) that occurs in nature as a toxic liquid that produces a highly irritating vapor. It is used in dyes, in developing photographs, and as an additive in gasoline.

Bronchitis—Inflammation of the bronchi, or tubes, that lead to the lungs. Symptoms include fever, chest pain, and cough. It can be caused by a virus, bacteria, or by irritants in the air, such as pollution or tobacco smoke.

Bt—An insecticide with a genetically-engineered (GE) bacterium (Bacillus thuringiensis, or Bt) that farmers use to combat several kinds of caterpillars.

Building codes—Rules that tell people how to design and construct houses and other structures in order to insure that structures are safe and environmentally and socially appropriate.

Bycatch—Fish, sea turtles, coral, sponges, and other marine life that fishermen harm or kill while trying to catch other seafood. Fishing practices that result in bycatch are referred to as "dirty fishing".

C

Calcium—A chemical (chemical symbol Ca) that strengthens bones and teeth and is found in dairy foods, leafy vegetables, and other foods. It occurs naturally in the environment in materials such as coral reefs and limestone and makes up about 3% of the Earth's crust.

Calories—Units of measurement used to indicate the potential amount of energy provided to the body by a particular food. Exercise and a good diet help prevent calories from turning into fat. Also referred to as kilocalorie. Kilocalories is a unit of energy equal to 1,000 calories, which is the amount of energy needed to raise the temperature of one kilogram of water one degree Celsius.

Campylobacter jejuni or coli—A bacteria transmitted by contact with animals and animal feces, usually from contaminated food, which causes Campylobacteriosis. This disease causes mild to severe infection of the gastrointestinal system, including diarrhea, fever, cramps, nausea, and vomiting.

Canal—A human-made waterway that is used for draining land, bringing water to crops by irrigation, and navigation.

Cancer—An uncontrolled growth of cells that crowds out and destroys healthy tissue, sometimes caused by cancer-causing agents.

Cancer-causing agents—Substances—like tobacco and certain chemicals— that can affect the human body in ways that lead to cancer.

Carbon dioxide—A colorless, odorless, nonpoisonous gas (chemical symbol CO2) found in the air in small amounts. Humans exhale it, and trees and other plants absorb it and use it to make food. Cutting down trees or burning fossil fuels, such as oil and coal, increases carbon dioxide in the atmosphere. It is a greenhouse gas that contributes to global warming, which, in turn, affects human health. It also creates the bubbles that are found in soda and other carbonated drinks.

Carbon monoxide—A colorless, odorless, poisonous gas (chemical symbol CO) released into the air when organic materials, such as oil, coal, and wood, are burned. The more that oxygen is restricted during the burning process, the more carbon monoxide will be created.

Carbonic Acid—A very weak acid (chemical formula is H2CO3) formed when carbon dioxide gas dissolves in water. This process occurs naturally when a body of water such as an ocean traps carbon dioxide. Commercial bottlers use this process to make drinks "carbonated" or bubbly. Carbonic acid is often found in groundwater, and is responsible for the formation of most caves.

Cash crops—Crops that farmers grow to sell rather than to use as food for themselves or as livestock feed.

Cataracts—A clouding or darkening of the lens of the eye. A cataract, when untreated, permanently blurs vision. Cataracts occur naturally in the elderly, but exposure to too many ultraviolet rays can cause them in anyone. It is important to wear sunglasses that provide UV protection in bright sunlight.

Cell—The smallest structural and functional unit that makes up all living things. (An exception is viruses, which are regarded as “living” only once they enter a cell.)

CFCs (chlorofluorocarbons) —Compounds consisting of chlorine, fluorine, and carbon. CFCs are found as coolants in refrigerators and air conditioners. CFCs released into the atmosphere are one of the causes of holes in the ozone layer, leading to global warming and other environmental problems. One chlorine atom from a CFC can destroy more than 100,000 ozone molecules. A leaky air conditioner that uses CFCs can destroy millions of ozone molecules.

Chagas' disease—A tropical disease caused by Trypanasoma parasites and spread by triatome beetles. Symptoms include high fever and damage to heart muscle.

Chemical—Refers to human-made or synthetic compounds—or not of natural origin.

Chickenpox (Varicella)—An infectious disease common in children under age 12. Fever and aching often accompany the itchy blisters or pocks that appear first on the abdomen, back, and face. Chickenpox is caused by the varicella-zoster virus (VZV). The chickenpox vaccine or combination MMRV (measles, mumps, rubella, varicella) vaccine and booster shot later on provide protection. People usually have one episode (develop immunity) but the virus itself can remain dormant, linger in the body and later, under certain circumstances, develop into shingles (herpes zoster).

Chlorine—A poisonous, odorous element (chemical symbol Cl) that is found naturally as a gas. It is capable of combining with nearly all other elements. Chlorine is used in compounds such as bleach and chloroform, as well as in pesticides such as DDT.

Cholera—A serious and often deadly infectious disease of the small intestine. Symptoms include diarrhea and vomiting, and the resulting dehydration can cause death. This disease is rare in richer nations but is frequently found in poor areas where treated drinking water is not available. Outbreaks often occur either after flooding because the water supply becomes contaminated, or following periods of warm sea surface temperatures. (see copepods)

Climate—Climate is the expected long-term weather found in a region, such as a hot, dry desert or the cold, snowy arctic.

Climate change—Climate is the expected long-term weather found in a region, such as a hot, dry desert or the cold, snowy arctic. Often called global warming, climate change refers to: 1) raising of global temperatures; 2) increasing extremes of the hydrologic (water) cycle, which result in more frequent floods and droughts; and 3) rising of sea level due to thermal expansion of the oceans salt water.

Climatologists—A scientist who studies climate.

Closed system—Earth is a closed system in which no matter or energy can leave or enter from the outside. Water and energy can be changed from one form to another, but none can be created nor destroyed. The resources that are on Earth now are all that we will ever have, so taking good care of them is important.

Commodity—Any product of agriculture or mining that is produced to be traded or sold, such as cash crops. It can be a food, a fiber such as cotton, or tobacco, gold, copper, etc.

Communicable—A disease that can be transmitted very quickly from person to person. A communicable disease, such as chickenpox, is both contagious and infectious. Both words generally mean the same thing.

Companion planting—Locating plants, or fields of plants, close to each other, to take advantage of each one's natural ability to attract beneficial insects, repel harmful ones, aid or discourage growth, and take advantage of certain chemical interactions among plants. For example, the roots of one plant can release chemicals into the soil that can benefit the health of plants nearby.

Composting—Gathering together various types of plant material (e.g., leaves, grass clippings, food waste, sawdust)—usually in a pile—so that heat will break down the materials into a rich brownish-black product called compost. This is then used to naturally fertilize and improve the structure of soil.

Compound—A substance composed of two or more molecules that are held together by chemical bonds. For example, water is a compound made up of two hydrogen atoms and one oxygen atom (chemical symbol H2O).

CAFO (Concentrated animal feeding operation)—See Factory (industrial-style) farms.

Conservation—The protection and careful use of resources and the environment.

Conservation tillage—A land cultivation method used to prepare soil for planting. It leaves some plant residues on the soil surface for erosion control and moisture conservation, instead of plowing them into the soil.

Contaminants—Substances—physical, chemical, biological, or radiological—that put air, water, soil, or food at-risk. Large concentrations of contaminants in animal feed can threaten human health.

Contaminated—Refers to air, water, soil, or food that has been polluted by dangerous chemicals or infectious microbes (viruses, bacteria, or parasites) so that it becomes unusable or harmful. These contaminants may be physical, chemical, biological, or radiological substances.

Copepods—Small crustaceans (arthropods) found in either salt or fresh water. Cholera bacteria have been found inside copepods.

Coral reef—Rock-like structures built by corals. Corals are small (inch-long) ocean animals. Young corals attach themselves to the limestone skeletons of dead corals. Over thousands and millions of years, layers of skeletons build up and grow into reefs. Reefs are home to a quarter of all ocean species. Called the rainforests of the sea, coral reefs are endangered.

Core samples—Cylinder-shaped samples of rock, ice, or other material from the center of an area drilled or cut into. The purpose of taking a core sample is to determine the composition or history of a geographic area.

Cornea—The tough, transparent covering that protects the eye. It can be damaged by too much exposure to ultraviolet rays or through injury.

Corneal photokeratitis—Sunburn of the cornea caused by too much exposure to ultraviolet rays or by looking at bright snow without eye protection (sometimes referred to as “snow blindness”). Symptoms are temporary loss of vision and eye pain.

Cover crops—Crops planted not for harvest but to improve soil quality, prevent erosion, and control weeds and insects. Such crops are usually tilled into the soil to improve fertility for the next food crop to be planted there.

Crop rotation—Alternating the crops grown in a given field from one growing season to the next. This is done because the alternating crops take different nutrients from the soil, or because one crop might restore particular nutrients that the other one takes away. Crop rotation can also interrupt the life cycles of pests or plant diseases that prey on a particular crop.

Crop yields—The amount of food produced from a certain land unit such as, 120 bushels of corn per acre.

Crossbreeding—Creating a new organism by crossing, or mating, two different varieties within a species.

Cross-pollination—The transfer of pollen from the flower of one plant to the flower of another for the purpose of fertilization. This can occur in nature or with human intervention.

Cyclosporiasis—An infection caused by a microscopic parasite. It affects the small intestines and is spread by water or food that that is contaminated with human feces.

Cryptosporidiosis—A disease caused by parasites spread through contaminated water. Found both in the developing and developed worlds, its symptoms include diarrhea, cramps, and fever, and dehydration can result. Water contamination by the parasite's spore (an “oocyst”) can come from waste of either humans or livestock. It is called crypto for short.

Cryptosporidium—A protozoan parasite found in water contaminated by sewage or runoff containing animal waste. It infects the intestines of animals and humans, and causes diarrhea, nausea, and cramps. It is resistant to chlorine, but can be removed through filtration (to 1 micrometer) or destroyed by boiling.

Cyclosporine—A medication, derived from a fungus, used to stop the immune system from rejecting a kidney or other transplanted organ. Also used to treat rheumatoid arthritis and other medical conditions.

D

Dead zone—Area of water containing low levels of oxygen in which fish, plants, and other aquatic life find it hard to survive. See hypoxia.

Deforestation—Destruction of forests, either by logging or burning down trees to make land for agriculture. Since trees provide oxygen and absorb carbon dioxide, destruction of forests affects the atmosphere and is often seen as a major cause of enhanced greenhouse effect. Deforestation also destroys animal habitats.

Dehydration—Excessive loss of water from the body. Mild symptoms include a dryness in the mouth and throat. More serious ones include the inability to sweat, low blood pressure, and fast heartbeat.

Delta—The fan-shaped area at the mouth, or lower end, of a river, formed by eroded material that has been carried downstream and dropped in quantities larger than can be carried off by tides or currents.

Dengue fever—A serious infectious disease caused by a virus carried by Aedes aegyptii mosquitoes and most often found in hot climates. Symptoms include rash, fever, headaches, and severe muscle and joint pain. The pain is so severe, its nickname is “breakbone fever.”

Dense—Refers to matter close together or thick. Examples include algae that have multiplied into a bloom, a forest with trees so close together that little or no light comes in, and populations in urban areas. A densely populated area has a large concentration of people, houses, and automobiles.

Desalinization—The process of transforming saltwater into freshwater so that it that can be used for irrigating farms and for human consumption (drinking, cooking, bathing). It is an expensive process, so it is not widely used.

Desertification—The change from once fertile land into desert.  Causes include overgrazing by animals, deforestation, drought, the burning of large areas of forests or other vegetation to make farmland, and the overuse of water for irrigation.

Developed—Describes nations or countries with social, cultural, industrial and technological advancement.

Developing—Describes regions and countries that are still in the process of acquiring modern technology and becoming economically productive. These regions are sometimes called the “Third World.”

Dinoflagellates—Reddish colored algae that swim by means of two hairlike structures called flagella. When the temperature and amount of salt in water increase, the number of these algae grows, causing what is called a red tide, or algae bloom, which then can block sunlight to underwater plants and animals and put toxins in the water.

Dioxin—Toxic, human-made chemical byproducts (dibenzo-p-dioxins), released into the atmosphere from incineration and during industrial processes that use chlorine. Dioxin tends to accumulate in the fatty tissue of fish. They can have immediate and long-term health effects, including skin disease, cancer, and reproductive failure.

Distribution systems—The networks of people and companies that transports, processes, and stores food from the farm before delivering it to stores or other entities that sell it to consumers. Good distribution systems are vital when shortages occur.

DNA—The compound, deoxyribonucleic acid, inside the cells of plants and animals that contains genetic information. It is through DNA that people inherit traits such as eye and hair color.

Drawdowns—The lowering of the water table, or level of groundwater. Drawdowns are evidence of decreasing amounts of available water.

Drip irrigation—A slow, even application of low-pressure water to soil and plants using plastic tubing placed directly at the plants' base. This method results in very little evaporation or runoff, saving water by directing it more precisely, reduced transmission of pathogens, and fewer weeds.

Droughts—A lack of precipitation over a long period of time, usually for a season or more. Too little water results in water shortages, which can affect people's ability to grow food and have enough clean, safe water. In extreme cases, it can lead to famine and malnutrition.

Drug resistance—The result of changes in microbes that reduce or eliminate the effectiveness of medicines that are designed to cure or prevent infections.

E

Ebola—A highly contagious infectious disease caused by an airborne virus and first noticed in Africa in the 1970s. Symptoms include muscle and joint pain, fever, organ failure and heavy bleeding. It is almost always fatal.

Ecolabels—An idea that has not yet been put into practice, they are labels or logos that would indicate that a product has met a set of environmental standards, or would inform the public of the benefits, risks, or potential damage done to our environment from the production, processing, and transportation of food products.

EcoHealth— Name of this Web site. The Web site is about how ecology (the study of the relationship of living organisms with each other and with their environment) and our health are intertwined. When we cause our environment to change, we can affect our health, too. The health of our planet is connected to our own health.

Ecology—The study of the relationship of living organisms with each other and with their surroundings.

Ecosystem—A community of plants and animals living in an area along with the things they need to sustain life, such as a place to live, food, and water. An ecosystem can be as small as a tiny tide pool or as large as a vast desert.

Ecosystem services—The benefits people obtain from ecosystems like food, water, and climate regulation. For example, intact wetlands filter toxic chemicals and can also serve as a protected nursery for young fish.

Ecotourism—Vacation or travel that tries to conserve the natural environment of a country or place, such as a rainforest or coral reef.

Eczema—A disorder of the skin like psoriasis and also considered to be related to malfunctions of the immune system. Symptoms include red, itchy skin and sores that ooze and crust over. One out of ten children develops eczema, but more than half of them lose it by the time they reach their teens.

Electromagnetic (E-M) spectrum—Electromagnetic waves show the relationship between the forces of electricity and magnetism. These waves move in regular patterns and include X-rays, light, radio waves, and ultraviolet rays. The electromagnetic spectrum arranges these waves from the shortest to the longest.

El Niño—Name given to the changes in direction of tropical winds over the Pacific Ocean and abnormal warming of the ocean's surface in the eastern Pacific that happen roughly every 3 to 7 years. This ocean warming can strongly affect weather patterns all over the world. El Niños often occur first during the Christmas season, which is where they got their name (El Niño means Christ child in Spanish). La Niña, is the opposite or “cold phase” of the El Niño cycle.

Endangered species list—A list of animals and plants in danger of becoming extinct.

Endocrine—System of the human body that releases hormones into the blood stream or lymph system. These hormones control growth, metabolism, mood, and reproduction and influence almost every cell and organ in our body.

Endocrine disruptors—Substances that stop the production or block the transmission of hormones in the body.

Endospores—Dormant, non-reproductive structure produced by some bacteria. Because even after being dried out or heated, they can grow again, they are attractive to bioterrorists.

Energy inputs—The amount of energy used to produce a product.

Enterococcus faecium (E. faecium)—A vigorous bacteria, normally found in the digestive tract of humans and other organisms. One species, E. faecium is resistant to antibiotics. E. faecium infection can cause complicated abdominal infections, skin infections, and infections of the urinary tract and blood stream.

Enzymes—Proteins that the body produces naturally. Enzymes help the body with many functions such as breathing, digesting food, and moving muscles.

Epidemics—An outbreak of an infectious disease that becomes widespread very quickly, affecting many people at the same time in a region or a country. Pandemics affect a much larger area and last a longer time. Diseases that are widespread in a region and are always present, such as malaria in Africa, are called endemic.

Epidemiology—Study of the incidence and distribution of disease in human populations and the influence of the environment and lifestyle on disease patterns. Epidemiologists are physicians or scientists who study the incidence, transmission, and control of disease in particular populations in order to identify and alleviate health problems. Epidemiological evidence is proof of their findings.

Eroding—Process of wearing or grinding down land surfaces by water, wind, or ice.

Erosion—The wearing away of soil or rock by forces such as wind, rain, or glaciers. Cutting down trees increases erosion because the soil no longer has any roots to hold onto.

Escherichia coli (E. coli)—A species of bacterium found in the healthy intestinal tracts of humans and other animals. It crowds out disease-causing bacteria and produces Vitamin K. However, a mutant strain of E. coli, found in undercooked beef, is very dangerous, can cause severe disease that can become fatal in small children and the elderly.

Evaporation—The natural process by which water turns from a liquid into a gas as it is absorbed into the air. When irrigation water evaporates, it leaves behind salts and other minerals, which contribute to salinization of the soil, making it unsuitable for farming.

Evolution—Gradual changes to groups of organisms over time.

Extinct—Refers to once living species that no longer exist.

F

Factory (industrial-style) farms (also known as concentrated animal feeding operations, CAFOs)—Animal producing farms that confine thousands and even hundreds of thousands of animals into one facility. Animals are not treated humanely. Due to the over-crowded conditions and diseases, the animals are fed antibiotics. They are not allowed to graze or eat at will. They are fed in feedlots and are given growth hormones to speed their growth. Such farms also threaten groundwater, lakes, rivers, air, and soil.

Falciparum—The most serious form of malaria. It can attack the brain and is often fatal.

Fallow—Refers to planting nothing in land where crops are usually grown.

Famine—Drastic, wide-reaching, long-term shortages or lack of food caused by the regional failure of food production or good distribution systems. Starvation and disease can result.

Feedlots—Confined or fenced-in land areas, devoid of grass or other vegetation, where livestock are kept and fattened for market. In these areas, the animals are completely dependent on an outside source for food. The large concentrations of animal waste that accumulate cannot be absorbed by the soil and often end up carried into nearby streams or lakes by rainfall runoff.

Fertile—Refers to land capable of sustaining abundant growth. For example, healthy plants grow in fertile soil.

Fertilizer—A substance that provides nutrients to plants. Some, such as manure, are natural; others are human-made or synthetic. Organic fertilizers come from natural sources, such as animals or vegetable substances. They also hold moisture, reduce soil erosion, and improve soil structure. They work very slowly and offer long-term benefits. Most synthetic fertilizers are derived from petroleum and are highly soluble.

Fiber—Ingredient in plant-based foods that aids digestion, controls blood glucose (sugar), helps rid the body of waste, and even may lower cholesterol. High-fiber foods such as vegetables, beans, and whole grains are healthier than low-fiber cereals and processed foods.

Filter feeders—Animals, such as clams and scallops, that filter small amounts of nutrients—mostly from plankton, bacteria, or wastes—from large volumes of water.

Fishing factories—Huge fishing industry ships, operated by crews of 500 to 650 and accompanied by their own fleets of smaller ships called catcher boats. Some factory ships can remain at sea for months at a time and can process and store huge amounts of catch.

Floodplains—A flat area on both sides of a stream or river that becomes covered with water when floods occur.

Floods—Excess water that overflows onto land that is normally dry.

Food chain—A way of showing the food relationships among organisms. The food chain describes what eats what. An example would be that zebras eat grass and lions eat zebras. A food web is the weaving together of food chains, showing all the food relationships in a given area. Any animal eating any part of a food chain is included in the food web.

Food insecurity—Uncertain or limited availability of adequate supplies of nutritional and safe food.

Food miles—The distance food travels from where it is grown or raised to where it is ultimately purchased by consumers.

Food production system—Method for growing food, including raising crops and animals. It incorporates biological, land, and labor resources. Sustainable agriculture is one form.

Former Soviet Union—Fifteen independent countries (with Russia being the largest) created from the Soviet Union—also known as the USSR, Union of Soviet Socialist Republics, until its breakup in 1991.

Fossil aquifers—Non-renewable aquifers, found mostly in arid climates, with no river or other source of recharge. Groundwater gets trapped in these underground rock formations with no natural way to escape. This water can be hundreds, thousands, or even millions of years old. These aquifers aren't sustainable since any withdrawal permanently depletes them.

Fossil fuels—Made from plants and animals that have decayed and turned into fuels such as natural gas, oil, and coal. Fossil fuels take millions of years, and extreme pressure and heat from the Earth, to be formed. When burned, they are a leading cause of greenhouse gases and global warming.

Fragmentation—See habitat fragmentation

Frozen-at-sea (FAS)—Refers to seafood frozen within four hours of being caught and stored at temperatures well below freezing to prevent decay.

Fungi—Plantlike organisms that lack chlorophyll and so must take nutrients from their environment rather than make their own food. Fungi range from tiny molds and yeasts to mushrooms. Fungi is the plural; fungus is the singular.

Fungicides—Human-made or natural chemical compounds used to kill unwanted fungi.

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GATT (General Agreement on Tariffs and Trade)—An agreement signed in 1947 by 23 countries, including the U.S., to increase international trade and economic growth. With more than 100 members today, it reduces tariffs and other barriers to trade. In 1994, GATT created the World Trade Organization (WTO) to enforce the agreement. Member countries must treat other members equally, consult on trade matters, and resolve differences peacefully.

GE food—GE food is also known as bioengineered or transgenic food, produced using the genetic engineering process.

Gene—The hereditary unit in a cell that determines a living being's characteristics. It can mutate, causing changes in the organism. A gene is made up of DNA. Understanding how genes work is one of the major areas in which medicine is advancing.

Gene pool—All of the genetic information that exists in a species at a given moment in time. The gene pool can expand or contract. For example, if all members of a species with a given genetic trait die out, that trait no longer exists, and the gene pool has grown smaller.

Genetically modified (GM)—All human-designed changes in a plant or animal, whether done through traditional breeding or genetic engineering. Genetically modified and genetically engineered are sometimes used interchangeably.

Genetic engineering (GE)—The process by which scientists move a genetic sequence (one part of a gene) from one species and insert it into the DNA of another species, thus changing one or more traits of the receiving organism. Differs from traditional breeding, such as cross-pollination.

Genetic erosion—Loss of genetic diversity within the same species over time, due to human intervention or environmental change.

Genetic pollution—The unintended transfer of genetic material from a genetically engineered organism to one that is not genetically engineered.

Giardiasis—A disease spread by water contaminated with animal or human waste containing a harmful protozoan. Symptoms include diarrhea, cramps, and weight loss. Long known as a widespread disease in humans, there is now concern that tourists and other people have unintentionally spread the disease to gorillas in Africa.

Glaciers—A large body of ice that forms through the tight packing and freezing of snow and then advances and recedes slowly due to its enormous weight and the pull of gravity, changing the shape of the land as it moves.

Gleaning—To collect and use unharvested crops from fields instead of wasting them. It also describes obtaining unused agricultural products from food processors and retailers, usually for distribution by charitable food banks.

Gluten—The sticky plant protein substance that remains when starch is removed from grains such as wheat, rye, corn, barley, and oats. The gluten in flour is what helps baking dough stick together. It also is used as an adhesive and an additive in pet food and animal feed.

Global positioning system (GPS)—A radio navigation system that locks into orbiting satellite signals and reads shifts in radio waves to determine by mathematical formula the exact location of a person or object on Earth. It can keep hikers from getting lost and measure crop output on small farms. The GPS receiver can be hand-held or integrated into a larger machine.

Global surface temperature—Average temperature of the Earth's surface. This chart from NASA shows the change in the global average surface temperature since 1880.

Global warming—Also called climate change. The slow increase of the Earth's surface temperature. It has resulted from both natural causes such as warming during an interglacial period and from the increased release of human-made greenhouse gases into the air through the burning of fossil fuels. Extreme or abrupt changes in climate may also occur, rather than just gradual warming.

Globalization—A process by which people, products, ideas, and diseases move around the world more easily and quickly, even to and from previously remote areas. At the core of this is an increased integration and interdependence between and among countries.

Gray water—Water that has been used for one purpose, such as laundry, which can then be used to irrigate or water crops. Handling gray water properly is important for public health; toilet water is not gray water.

Greenhouse gases—Gases that act like the glass walls of a greenhouse, letting sunlight through, but trapping infrared heat energy in Earth's atmosphere. Some greenhouse gases, such as water vapor, keep harmful ultraviolet rays out and allow the sun's energy in. Others, such as CFCs, are very powerful greenhouse gases that are not naturally occurring and are let into the atmosphere through the use of aerosol sprays. Major human-generated greenhouse gases include: carbon dioxide, methane, and nitrous oxide. Carbon dioxide is released to the atmosphere when solid waste, fossil fuels (oil, natural gas, and coal), and wood products are burned. Methane is released during the production and transport of coal, natural gas, and oil. Methane emissions also result from the decomposition of organic wastes in landfills, and the raising of farm animals. Nitrous oxide is emitted during agricultural and industrial activities, as well as during combustion of solid waste and fossil fuels.

Green Revolution—The introduction of pesticides, irrigation, high-yield grains, and better farm management during the 1960s and 1970s, which greatly increased agricultural productivity and was intended to help solve the problem of hunger in developing countries.

Groundwater—Water that seeps down from the surface of the ground (from rain and snowmelt) and then is stored and transported underground, often in an aquifer. All fresh water that does not either evaporate or flow into a river, stream, or sewer becomes groundwater.

Growth hormone—A substance (somatotropin) that stimulates the growth of almost all cells and tissues of an animal or human.

H

Habitat fragmentation—The breaking up of spaces that are home to animals into smaller and unconnected segments (due, for example, to a subdivision being built in the middle of a forest, a road through a meadow, or a dam across a river). This can result in the loss of habitat as well as the disruption of an ecosystem.

Hantavirus—Virus carried by rodents that causes bleeding and kidney failure. A variant called Hantavirus Pulmonary Syndrome was discovered in the American Southwest in the 1990s, and causes a serious lung infection and death in nearly half of those who become infected. People catch the disease by breathing in particles from the rodents' droppings (not from bites).

Heat exhaustion—An illness that occurs from too much activity or too much time in the heat. A person's body temperature reaches above normal levels, and as a result, the person can lose too many body fluids, have a headache, feel overly tired, and even pass out.

Heatstroke—An illness that occurs when a person's reaction to the sun or heat is so extreme that the body can no longer sweat. A high fever, coma, and even death can result.

Heavy Metals—Dense elements with a high mass and atomic weight. They tend to be toxic and bioaccumulate. In small concentrations, exposure to certain metals can be very dangerous. Once in the environment, they don't decompose. Mercury, lead, and cadmium are particularly harmful; gold is not. Living organisms need trace amounts, such as iron, copper, and zinc, to survive.

Hepatitis—A disease of the liver (often fatal) usually caused by a virus, but also by bacteria, parasites, or by drinking too much alcohol. Symptoms include abdominal pain, flu-like symptoms, and yellowish (jaundiced) skin. Scientists continue to discover new types of Hepatitis viruses. Hepatitis A, B, and C are most common. Hepatitis A comes from consuming contaminated food or water. Hepatitis B and C can be transmitted through sexual contact or intravenous injection (sharing needles or blood transfusions.)

Herbicides—Chemicals used to kill or control weeds.

Hibernation—A sleeplike state that some animals enter in winter. The body temperature lowers and the heartbeat slows, allowing the animal to live off the fat stored in its body for a prolonged time.

Hidden hunger—Vitamin and mineral shortages and other food inadequacies that can harm people's health and affect their ability to learn, but which are not apparent from more familiar signs of severe malnutrition and starvation.

High blood pressure—Blood pressure is the measurement of the force of the blood on the arteries as the heart pushes the blood through the body. High blood pressure is when there is too much pressure, which can lead to heart and kidney problems.

High-yield crops—Fruits and vegetables that bring a high profit when taken to market; this profit is immediate and short-term and does not take into account the long-term consequences of the farm practices used.

HIV/AIDS—Human Immunodeficiency Virus (HIV) and Acquired ImmunoDeficiency Syndrome (AIDS). HIV is the virus that causes AIDS. Immunodeficiency means having a faulty immune system so that a person can become very ill or die from a disease that others can fight off. HIV is passed from person to person through blood or other bodily fluids, either through a transfusion of infected blood, to a baby from its mother, through use of contaminated hypodermic needles, or through sexual contact with a person who has the disease.

HIV/Positive—Detection that a person has this virus in their blood. The person may not come down with AIDS but can carry HIV for years and infect other people.

Hodgkin's disease—A malignant lymphoma or cancer of the lymphatic system that causes an improper functioning of the lymph tissues and white blood cells. Symptoms include enlarged spleen and liver, fever, anemia, weight loss, and night sweats. Named after Dr. Thomas Hodgkin who published studies of the disease in 1832.

Hormone disruptors—Substances or chemicals in the environment, which mimic hormones, thus blocking the natural transmission of hormones. A range of hormones are produced by the endocrine glands and transported by body fluids to regulate and stimulate cellular activity throughout the body.

Host—To serve as a home in which a disease agent either multiplies or goes through a stage of its life cycle. When protozoans or worms such as blood flukes, for example, live inside a snail or a human, that snail or person is considered a host. Hosts in which a disease agent builds up and multiplies are called “reservoir” hosts (mice in the case of plague, hantavirus, and Lyme disease, or birds in the case of West Nile virus).

Hurricanes—A tropical storm, with winds over 74 mph that usually also has rain, thunder, and lightning. Hurricanes are common along the east coast of the United States and the Gulf of Mexico. Hurricanes require warm ocean surface temperature to begin to form. In other parts of the world hurricanes are called “typhoons.”

Humus—That organic portion of the soil formed by the complete decomposition of animal or vegetable matter. It provides nutrients and microorganisms for plants and increases the ability of soil to retain water.

Hydrocarbons—Chemicals formed from hydrogen and carbon. Fossil fuels such as natural gas and oil are made up of these compounds. These fuels provide heat (in buildings), light, and power (used in cars and in plants that generate electricity). When burned, hydrocarbons release pollutants into the atmosphere.

Hydroelectric stations—A place where electricity is created using the force of large quantities of water, usually from a river. Water is allowed to fall through machines called turbines, which turn under the pressure of water and create electricity. After the water is used, it returns to the river, where it can be used again.

Hydroponics—The growing of plants, especially vegetables, in water containing essential mineral nutrients rather than in soil.

Hypothesize—To form a hypothesis, a possible explanation for a set of facts that is then tested by performing an experiment or investigation.

Hypoxia—A low level of oxygen often resulting from the flow of agricultural run-off into rivers, lakes, and oceans. This condition stifles or kills aquatic life. See dead zone.

I

Ice age—Ice age with lowercase letters means a period of time when large segments of the Earth's surface were covered by enormous ice sheets known as glaciers. Ice Age with capital letters means the longest and most widespread ice age. This occurred in the Pleistocene Era (2 million to 11,500 years ago). It was during this ice age that the majority of the Earth's surface was covered by glaciers. Animals, such as the saber-toothed tiger and woolly mammoth, roamed freely.

Ice jams—A build-up of broken ice in a river channel that partially blocks the flow of water and keeps boats from transporting goods and people.

Immigrants—People coming into a country from another country for political, economic, or personal reasons. Immigrants tend to be permanent, whereas migrants often move on a seasonal or temporary basis. Emigrants are people who leave a country.

Immune proteins—Chemicals found in cells that have contact with the bloodstream. These chemicals attack microbes and keep organisms safe from disease. An example is squalamine, found in sharks.

Immune system—The defense system of the body made up of multiple organs and cells that protects the body against disease and fights off infection and illness.

Immunity—The ability—inherited, acquired through exposure, or induced through vaccination—of an organism to fight disease. Immune response is the general reaction of the body to substances that the body treats as foreign.

Indigenous—Originating or occurring naturally in—native to—a specific place or area.

Industrial agriculture—Modern farming methods that depend on synthetic fertilizers and pesticides, large amounts of irrigation water, major transportation systems, factory-style practices for raising livestock, and machine technology. It contrasts with sustainable agriculture.

Industrial revolution—A dramatic change in the ways people earned money and made goods that began in England around the mid-1800s. People went from making goods in their own homes with simple tools to making them in large-scale factories with complicated machinery. As a result, many rural regions became more urban as cities grew rapidly around the new industrial activity.

Inert—Refers to unmoving or unchanging. In chemistry, this means an element that rarely combines with other elements. In medicine, it means a substance that has little or no effect on the human body.

Infectious diseases—A disease that can be spread directly or indirectly from one living thing to another, such as meningitis, malaria, strep throat, and influenza (the flu). Emerging infectious disease: An illness that presents new challenges in the 21st century and has one of the following characteristics: 1) previously unknown or not affecting enough people to get attention; 2) familiar but now affecting far more people; 3) appearing in new or unexpected regions; 4) resistant to antibiotics that once controlled it.

Inflammation—A response anywhere in the body to injury and to invasion by bacteria or viruses. The area affected is often red and swollen as the body heals the injured tissue or fights the infection.

Influenza (Flu)—A contagious disease of the respiratory tract (nose, throat, lungs) caused by one of three strains of influenza virus (A, B, and C). Symptoms include sore throat, muscle pains, headaches, cough, fever, and fatigue. In addition to suffering and death, an epidemic can impose economic hardships in the form of health care costs and lost productivity. Worldwide flu pandemics occurred in 1918, 1957, and 1968.

Innate immunity (genetic, inherent, or natural immunity)—The body's natural response to fighting disease. It is the body's first line of defense against infection. Skin, mucus, and nose hair act as physical barriers to keep microbes from entering. It is how the body fights and attacks microbes or any foreign object. It does not arise from a previous infection or vaccination.

Insecticides—Preparations, natural or human-made, used to kill insects.

Integrated pest management—An ecology-based system of pest control that uses natural predators, pest-resistant plants, and other methods to preserve a healthy environment in an effort to decrease reliance on harmful pesticides.

Intravenously—Refers to how a substance is put into the bloodstream by injecting it directly into a vein.

Invertebrates—Animals having no backbone, a category that makes up more than 97% of all animals. Some, such as worms, have no skeleton. Others, such as insects, have skeletons on the outside of their bodies.

Ionizing radiation—Radiation that knocks an electron from a molecule, thereby making it positively charged. The free electrons can form charged ions in living tissue that react with and damage cells. It can be used to destroy microorganisms and germs in food products.

Ions—Electrically-charged atoms or molecules.

Irradiation—Use of radiation to destroy microorganisms, bacteria, and germs in food products to prevent food-borne illnesses and to lengthen the shelf life of products. This process is controversial because some people are unsure of the long-term health effects of radiated food.

Irrigated—Land that has been artificially supplied with water for agriculture or landscaping usually through ditches, pipes, or by diverting rivers.

Irrigation—Artificially supplying land with water for agriculture or landscaping, usually through ditches, pipes, or by diverting rivers.

Irrigation canals—Long, narrow channels to carry water from a river, lake, or other source to farm fields.

Irrigation ditches—Trenches dug into land to allow water to flow, sometimes at a great distance from its source. This provides water for crops and for humans.

J