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  • Glossary
| Last Updated:15/10/2014



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Class of terrestrial vertebrates which lay their eggs (and also mate) in water but live on land as adults following a juvenile stage where they live in water and breathe through gills. Amphibians were the first group of land vertebrates; today they are mostly restricted to moist habitats.


A chemical released at neuromuscular junctions that binds to receptors on the surface of the plasma membrane of muscle cells, causing an electrical impulse to be transmitted. The impulse ultimately leads to muscle contraction.


The posterior opening of the digestive tract.


Reflectance; the ratio of light from the Sun that is reflected by the Earth's surface, to the light received by it. Unreflected light is converted to infrared radiation (heat), which causes atmospheric warming (see "radiative forcing"). Thus, surfaces with a high albedo, like snow and ice, generally contribute to cooling, whereas surfaces with a low albedo, like forests, generally contribute to warming. Changes in land use that significantly alter the characteristics of land surfaces can alter the albedo.


A group of hormones involved in controlling plant growth and other functions; once thought responsible for phototropism by causing the cells on the shaded side of a plant to elongate, thereby causing the plant to bend toward the light.


With abnormally low levels of oxygen.


The ability of molecules of one substance to adhere to a different substance.


Refers to organisms that synthesize their nutrients and obtain their energy from inorganic raw materials


An organism that produces complex organic compounds from simple inorganic molecules using energy from light or inorganic chemical reactions.

Anaerobic digestion

The biological degradation of organic materials in the absence of oxygen to yield methane gas (that may be combusted to produce energy) and stabilised organic residues (that may be used as a soil additive).

Aerobic digester

An aeration tank that is used to treat waste activated humus or primary sludges or a mixture of them, usually in a small plant with extended aeration or contact stabilization treatment. A typical operational problem associated with an aerobic digester is pH control. For example, when pH drops, this may indicate normal biological activity or low influent alkalinity. This problem is corrected by adding alkalinity, i.e. lime, bicarbonate, etc.

Agenda 21 global sustainable development

The global sustainable development agenda set out in the Rio Declaration on Environment and Development, which was established at the Earth Summit in 1992. Agenda 21 consists of 40 chapters, and at its roots are 27 principles. There are four broad sections which cover a range of issues: social and economic dimensions; conservation and management of resources for development; strengthening the role of major groups; and implementation. Agenda 21 highlights the importance of national strategies with international cooperation. It concludes proposals for the integration of environment and development issues in decision making and provisions for international institutional arrangements and legal mechanisms. Agenda 21 is an important document which has broad support among nations on all aspects of environment related to social and economic growth.

Anganwadi and school toilet facilities

Schools and in particular Anganwadis [Anganwadi workers and helpers are the grassroots level functionaries at village level for delivery of services under Central and State Government (of India) Schemes] are equally important places to address the health issues of the children provided that necessary infrastructure is available. Improved health and quality learning are not possible in schools and Anganwadis as long as basic hygiene is lacking or sanitary facilities and water supply are missing or broken or not properly used. Lack of healthy environment is already resulting in high infant mortality and under five-mortality rate. There are approx. 6 lakh Anganwadi Centers in India and most of them are without toilet facilities. These Anganwadi Centers reach out to 12.5 million children (ICDS, MoHRD).

Aquaprivies Latrine

LAn aquaprivy is a tank filled with water into which excreta fall via a drop pipe. Aquaprivies use a simple water seal to prevent odours getting out of the tank and have a soak away to dispose of sullage and effluent. It is important that the drop pipe reaches below the surface of the water in the tank to prevent the escape of odours. The tank should be watertight to prevent pollution of groundwater and requires emptying about every three years.

Air Pollution

Five major classes of pollutants are discharged into the air: carbon monoxide, particulates, sulfur oxides, hydrocarbons, and nitrogen oxides. In addition to the automobile, other major sources are from combustion of fuel in electric power plants, industrial processes, and space heating, from the combustion in solid-waste disposal, coal-waste fires, and agricultural burning.

Application efficiency

(sustainability) the efficiency of watering after losses due to runoff, leaching, evaporation, wind etc.


Requiring air or oxygen; used in reference to decomposition processes that occur in the presence of oxygen.


Tiny, thin-walled, inflatable sacs in the lungs where oxygen and carbon dioxide are exchanged.


Solid or liquid particles suspended within the atmosphere.


Reducing the degree of intensity of, or eliminating, pollution


The process of an organism adjusting to chronic change in its environment.

Alternative energy sources

Energy that does not come from fossil fuels (such as coal, oil, gas), for example wind, flowing water, solar energy and biomass.


(Sustainability) an ecologically based farming system, that, through the integration of trees in farms, increases social, environmental and economic benefits to land users.


The cultivation of aquatic organisms under controlled conditions.


The condition of receiving sparse rainfall; associated with cooler climates because cool air can hold less water vapor than warm air. Many deserts occur in relatively warm climates, however, because of local or global influences that block rainfall.

Arable land

Land that can be used for growing crops.

Algal Blooms

Sudden spurts of algal growth, which can affect water quality adversely and indicate potentially hazardous changes in local water chemistry.


Simple rootless plants that grow in sunlit waters in proportion to the amount of available nutrients. They can affect water quality adversely by lowering the dissolved oxygen in the water. They are food for fish and small aquatic animals

Air pollution

Air is made up of a number of gases, mostly nitrogen and oxygen and, in smaller amounts, water vapour, carbon dioxide and argon and other trace gases. Air pollution occurs when harmful chemicals and particles are emitted to the air – due to human activity or natural forces – at a concentration that interferes with human health or welfare or that harms the environment in other ways.


The invisible gaseous substance surrounding the earth, a mixture mainly of oxygen and nitrogen.

Alternative energy sources

Energy that does not come from fossil fuels (such as coal, oil, gas), for example wind, flowing water, solar energy and biomass.


Non-living chemical and physical factors of the environment


The atmosphere is a layer of gases which surrounds the entire Earth. It consists mainly of Nitrogen, Oxygen, as well as a few other gaseous elements. The purpose of this "layer" around the Earth is to prevent excessive amounts of radiation from reaching the Earth, thereby allowing we, as animals/planets, to survive. A planet such as Mars has very little, if any, atmosphere and hence has little or no life on it (at least as we see it now).


To impregnate with gas, usually air.


Substances produced by some microorganisms, plants, and vertebrates that kill or inhibit the growth of bacteria.


Genetic condition caused by the body's inability to manufacture pigments; an autosomal recessive trait.

Afforestation -

Planting new forests on lands that have not been recently forested.


With abnormally low levels of oxygen.


A bed or layer yielding water for wells and springs etc.; an underground geological formation capable of receiving, storing and transmitting large quantities of water. Aquifer types include: confined (sealed and possibly containing “fossil” water); unconfined (capable of receiving inflow); and Artesian (an aquifer in which the hydraulic pressure will cause the water to rise above the upper confining layer).


The protein from which microfilaments are composed; forms the contractile filaments of sarcomeres in muscle cells.


An organism that synthesizes food molecules from inorganic molecules by using an external energy source, such as light energy.

arithmetic growth

A pattern of growth that increases at a constant amount per unit time, such as 1, 2, 3, 4 or 1, 3, 5, 7.

Adenosine triphosphate (ATP)

A common form in which energy is stored in living systems; consists of a nucleotide (with ribose sugar) with three phosphate groups. The energy coin of the cell.


One of the four nitrogen-containing bases occurring in nucleotides, the building blocks of the organic macromolecule group known as nucleic acids (DNA and RNA). Adenine is also the base in the energy carrying molecule ATP (adenosine triphosphate) which is the energy coin of the cell.


A severe allergic reaction in which histamine is released into the circulatory system; occurs upon subsequent exposure to a particular antigen; also called anaphylactic shock.


Collective term applied to all of the male (stamen) parts of the flower.


A symbiotic relationship in which members of one population inhibit the growth of another population without being affected.


An extinct group of animals that were part of Cambrian-aged reef environments, but which were extinct by the close of the Cambrian Period


A Animal Kingdom. Multicellular eukaryotic group characterized by heterotrophic nutritional mode, usually organ and tissue development, and motility sometime during the organism's life history.


A disorder in which breathing stops for periods longer than 10 seconds during sleep; can be caused by failure of the automatic respiratory center to respond to elevated blood levels of carbon dioxide.


Chemicals produced by plants as a defense mechanism; inhibit the action of digestive enzymes in insects that attack and attempt to eat the plants.


Long fibers that carry signals away from the cell body of a neuron.


A method of prenatal testing in which amniotic fluid is withdrawn from the uterus through a needle. The fluid and the fetal cells it contains are analyzed to detect biochemical or chromosomal disorders.

Adaptive radiation

The development of a variety of species from a single ancestral form; occurs when a new habitat becomes available to a population. Evolutionary pattern of divergence of a great many taxa from a common ancestral species as a result of novel adaptations or a recent mass extinction. Examples: mammals during the Cenozoic Era after the extinction of dinosaurs at the close of the Mesozoic Era flowering plants during the Cretaceous Period diversified because of their reproductive advantages over gymnosperm and non-seed plants that dominated the floras of the world at that time


The process of changes in a living organism that help it adjust to the conditions of the environment, making it easier for animals to obtain food or shelter, or protect offspring.


A hormone secreted by the adrenal glands that controls the reabsorption of sodium in the renal tubule of the nephron.

Adventitious roots

Roots that develop from the stem following the death of the primary root. Branches from the adventitious roots form a fibrous root system in which all roots are about the same size; occur in monocots.

Attainment area

A geographic region where the concentration of a specific air pollutant does not exceed federal standards.


Early theory that held that some organisms originated from nonliving material.


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

Acquired immunodeficiency syndrome (AIDS)

A collection of disorders that develop as a result of infection by the human immunodeficiency virus (HIV), which attacks helper T cells, crippling the immune system and greatly reducing the body's ability to fight infection; results in premature death brought about by various diseases that overwhelm the compromised immune system.

Antibody-mediated immunity

Immune reaction that protects primarily against invading viruses and bacteria through antibodies produced by plasma cells; also known as humoral immunity.


Flowering plants. First appearing at least 110 million years ago from an unknown gymnosperm ancestor, flowering planbts have risen to dominance in most of the world's floras. The male gametophyte is 2-3 cells contained within a pollen grain; the female gametophyte is usually eight cells contained within an ovule which is retaind on the sporophyte phase of the plant's life cycle.

Analogous structures

Body parts that serve the same function in different organisms, but differ in structure and embryological development; e. g., the wings of insects and birds.


Porous, water-bearing layers of sand, gravel, and rock below the earth's surface; reservoirs for groundwater.


Division of fungi that contains the yeasts and morels; ascomycetes produce an ascus (or sac) in which ascospores are produced.


Refers to organisms that are not dependent on oxygen for respiration.

Axillary buds

Buds borne in the axil (where the leaf meets the stem) of a stem.

Appendicular skeleton

The bones of the appendages (wings, legs, and arms or fins) and of the pelvic and pectoral girdles that join the appendages to the rest of the skeleton; one of the two components of the skeleton of vertebrates.

Amniote egg

An egg with compartmentalized sacs (a liquid-filled sac in which the embryo develops, a food sac, and a waste sac) that allowed vertebrates to reproduce on land.

Asteroid impacts

Hypothesis that links certain mass extinction events with the impact of a comet or asteroid, most notably the mass extinction 65 million years that caused the disappearance of dinosaurs and many other reptilian groups. Asteroid impacts early in earth history also contributed to the formation of the atmosphere and oceans.

Apical meristem

A meristem (embryonic tissue) at the tip of a shoot or root that is responsible for increasing the plant's length.

Average megawatt (MWa or aMW)

One megawatt of capacity produced continuously over a period of one year. 1 aMW = 1 MW x 8760 hours/year = 8,760 MWh = 8,760,000 kWh.

Available water capacity

That proportion of soil water that can be readily absorbed by plant roots.

Activated sludge process:

A biological wastewater treatment process in which a mixture of waste water and activated sludge is agitated and aerated. The activated sludge is then separated from the treated wastewater by sedimentation and disposed of or returned to the process as needed.

Alternative fuels

Fuels like ethanol and compressed natural gas that produce fewer emissions than the traditional fossil fuels.


Molecules carried or produced by microorganisms that initiate antibody production; mostly proteins or proteins combined with polysaccharides.


In animals, a term referring to organisms that lack a general body plan or axis of symmetry that divides the body into mirror-image halves.


Ancient (over 3.5 billion years old) group of prokaryotes; some biologists want to place this group into a separate Kingdom, the Archaea. Most currently place it within the Kingdom Monera.


The artery that carries blood from the left ventricle for distribution throughout the tissues of the body. The largest diameter and thickest walled artery in the body.

Algal bloom

The rapid and excessive growth of algae; generally caused by high nutrient levels combined with other favourable conditions. Blooms can deoxygenate the water leading to the loss of wildlife.

Adaptive management area:

Landscape units designated for development and testing of technical and social approaches to achieving desired ecological, economic, and other social objectives.

Aeration basin:

A basin where oxygen is supplied by mechanical agitation or pneumatic means to enhance the breakdown of wastes held in suspension.

Animal Unit

(AU) A measurement of herd size used in the dairy industry. One animal unit is equal to 1000 pounds of animals. For example, a 1,200-pound cow equals 1.2 AU.


A compound that does not contain water. For example, fuel ethanol is referred to as "anhydrous ethanol" because most of the water has been removed.

Anadromous fish

Fish that hatch in freshwater, migrate to the ocean to mature, then return to freshwater to spawn. An example is salmon.


(sustainability) the first step in the waste hierarchy where waste generation is prevented (avoided).


Composite blend of materials made under special conditions. Metal alloys like brass and bronze are well known but there are also many plastic alloys.


A bed or layer yielding water for wells and springs etc.; an underground geological formation capable of receiving, storing and transmitting large quantities of water. Aquifer types include: confined (sealed and possibly containing “fossil” water); unconfined (capable of receiving inflow); and Artesian (an aquifer in which the hydraulic pressure will cause the water to rise above the upper confining layer).

Anabolic reactions

Reactions in cells in which new chemical bonds are formed and new molecules are made; generally require energy, involve reduction, and lead to an increase in atomic order.


Organisms that synthesize their own nutrients; include some bacteria that are able to synthesize organic molecules from simpler inorganic compounds.

atrioventricular (AV) node

Tissue in the right ventricle of the heart that receives the impulse from the atria and transmits it through the ventricles by way of the bundles of His and the Purkinje fibers.



 A way in which meiosis produces new combinations of genetic information. Paternal and maternal chromosomes line up randomly during synapsis, so each daughter cell is likely to receive an assortment of maternal and paternal chromosomes rather than a complete set from either.




Structure produced by sac fungi in which sexual ascospores develop.


Proposed, but not widely accepted, sixth taxonomic kingdom that would include the archaebacteria.

antibiotic resistance

Tendency of certain bacteria to develop a resistance to commonly over-used antibiotics.


Chest pain, especially during physical exertion or emotional stress, that is caused by gradual blockage of the coronary arteries.




Variation in chromosome number involving one or a small number of chromosomes; commonly involves the gain or loss of a single chromosome.