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Term Term description

The annual variation of seasons due to the tilt (between 22.1° and 24.5°) of Earth's angle to the axis.


An act or instance of attentive noticing or perceiving.

ocean acidification

When carbon dioxide (CO2) is absorbed by seawater, chemical reactions occur that reduce seawater pH, carbonate ion concentration, and saturation states of biologically important calcium carbonate minerals. Since the beginning of the Industrial Revolution, the pH of surface ocean waters has fallen by 0.1 pH units. Since the pH scale is logarithmic, this change represents approximately a 30 percent increase in acidity.


Not being connected to an electricity delivery, typical in rural or isolated locations.


An organism that eats both plants and animals.


A structure or part that is enclosed within its own membrane inside a cell and has a particular function. Organelles are found only in eukaryotic cells and are absent from the cells of prokaryotes like bacteria. The nucleus, mitochondrion, and chloroplast are examples of organelles.


Plant and animal residues, or substances made by living organisms. All are based upon carbon compounds.

Organic farming

The practice of growing plants without the use of synthetic pesticides, herbicides, and fertilizers, or of raising animals without the use of growth regulators, synthetic pesticides, feed that is produced using synthetic pesticides, herbicides, or fertilizers, and the like. Organic farmers and gardeners use short-lived, biodegradable pest-killers, biological pest control, rotation of crops, and manure and compost to control pests and provide plant nutrients.

Organic horizon

The top surface layers of soil dominated by the presence of large amounts of organic matter and litter in varying stages of decomposition.


An organic compound containing at least one covalently bonded atom of chlorine that has an effect on the chemical behavior of the molecule, and is found in highly toxic pesticides that are now largely banned in the West.


Any compound containing the trivalent group −PO4. (PO43-). This is a biologically available form of phosphorus.


The material that lies above an area of economic or scientific interest.


A chemical that has an affinity for electrons. An oxidant, when mixed with other substances, will draw electrons away from these substances and toward itself in a process called oxidation. Oxygen is an example of an oxidant, hence the origin of the word.


Oxygen is the third most abundant element in the universe and is a key requirement for the metabolic aerobic respiration functioning of organisms. Oxygen is also an important component of major organic molecules within organisms such as proteins, carbohydrates, and fats as well as inorganic compounds that make up hard tissue structures like animal shells, teeth, and bones.

ozone layer

A layer at altitudes between 15 km and 35 km in the earth's stratosphere containing a high concentration of ozone (O3), which absorbs most of the ultraviolet radiation from the sun before it reaches the earth.

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