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Term Term description
paddy farming

A paddy field is a flooded parcel of arable land used for growing semiaquatic rice, using  a small fraction of the total land yet feeding the majority of a population.


Climates in the geological past.


Paleoclimatology is the study of past climates. It is a multidisciplinary field combining history, anthropology, archaeology, chemistry, physics, geology, atmospheric, and ocean sciences.

An organism, usually an insect, that lives on or in a host organism during some period of its development and eventually kills its host.
particulate matter

Complex mixture of extremely small particles and liquid droplets in the air. Particle pollution is made up of a number of components, including acids (such as nitrates and sulfates), organic chemicals, metals, and soil or dust particles.

pastoral letters

An official letter of religious instruction from a Roman Catholic bishop or group of bishops to all the clergy and members of Church under their jurisdiction.


Peat is a heterogeneous mixture of partially decomposed plant (humus) material that has accumulated in a water-saturated environment and in the absence of oxygen. The warmer the climate, the quicker the plant material will decompose. It can be used as fuel after dried, and is a precursor to fossil fuel in the process of coal formation.


The outermost layer of the Earth's crust that is composed of soil. The pedosphere only develops when there is a dynamic interaction between the atmosphere (air in and above the soil), biosphere (living organisms), lithosphere (unconsolidated and consolidated bedrock) and the hydrosphere (water in, on and below the soil). The pedosphere is the foundation of terrestrial life on this planet.


The slow passage of a liquid through a filtering medium such as the percolation of rainwater through the soil.


Lasting for an indefinitely long time; plants that live for more than two years.

periodic table

A table that lists all of the known chemical elements on Earth, arranged according to their properties. It can be used to predict how they will react with other elements.


A layer of water-logged soil or bedrock that has been continuously frozen for at least two years and as long as tens of thousands of years. Permafrost can reach depths of up to 1,524 m (4,999 ft). It is predominantly found in the tundra biome and throughout most of the polar regions and underlies about one fifth of the Earth's land surface.

permanent components

The atmosphere contains consistent components such as Nitrogen and Oxygen that play an essential role in the protection and functioning of the planet.


The rate of flow of a liquid or gas through a porous material.


The ability of a material to allow the passage of a liquid, such as water. Permeable materials, such as gravel and sand, allow water to move quickly through them whereas unpermeable material, such as clay, does not allow water to pass through.


Chemicals that kill plant, animal and other "pests", and may also pollute food and water supplies. Well-known toxic pesticides include Aldrin, Chlordane and DDT.


pH is a measure of hydrogen ion concentration; a measure of the acidity or alkalinity of a solution. Aqueous solutions at 25°C with a pH less than seven are acidic, while those with a pH greater than seven are basic or alkaline. A pH level of is 7.0 at 25°C is defined as 'neutral' because the concentration of H3O+ equals the concentration of OH− in pure water.


The scientific study of periodic biological phenomena, such as flowering, breeding, and migration, in relation to climatic conditions.


The physical traits and appearance of an organism that are coded by its genetic makeup. The phenotype of an organism depends on which genes are dominant and on the interaction between genes and environment.

A highly reactive nonmetallic element occurring naturally in solid phosphate salts in white (or sometimes yellow), red, and black forms. It is an essential component of DNA, RNA and other important compounds in the protoplasm of cells. Phosphorus is commercially used to make fertilizers, matches, fireworks, and to protect metal surfaces from corrosion.
phosphorus cycle

The biogeochemical cycle that describes the movement of phosphorus through the lithosphere, hydrosphere, and biosphere.

photoelectric effect

The emission of free electrons from a metal surface when sufficiently energetic light strikes it.


The smallest particle of light or other electromagnetic energy, having no mass and no electric charge.


The interval in a 24-hour period during which a plant or animal is exposed to light.


The biochemical process by which green plants and some bacteria capture light energy and use it to produce chemical energy. Carbon dioxide and water are consumed during photosynthesis while oxygen and simple sugars are produced.

photovoltaic cells

A cell that converts solar energy into electrical energy.

photovoltaic effect

The effect observed when electromagnetic radiation, especially visible light from the sun, falls on a thin film of one solid deposited on the surface of a dissimilar solid producing a difference in potential between the two materials.


The primary subdivision of a taxonomic kingdom, grouping together all classes of organisms that have the same body plan.


Bioactive chemical compounds found in plants. Many phytochemicals have medicinal properties, and others are important sources of vitamins.


Microscopic, free-floating, autotrophic organisms that function as primary producers in aquatic ecosystems.

Planetary Commons

Physical space that includes the Earth processes, habitats and natural goods needed for biotic sustenance and well-being.


An aquatic organism that feeds on planktonic food, including zooplankton or phytoplankton. Planktivores can be microscopic in size or as large as the baleen whales that feed on plankton.


Primarily microscopic organisms that occupy the upper water layers in both freshwater and marine ecosystems, and include autotrophic (phytoplankton) and heterotrophic (zooplankton, bacteria, and protozoans).


Organisms whose habitat is the open water of oceans or lakes.

plant uptake

The process plants use to take water from the soil, or other medium, and deliver it to the rest of the plant's structure.

plate tectonics

The movement of large plates on the Earth's crust driven by convection in the Earth's mantle, the semi-liquid layer of superheated rock below the crust. Plate tectonics are responsible for volcanoes, earthquakes, and contribute to long-term changes in climate, and the current distribution of biological species on Earth.

polar desert

A biome with precipitation below 250 millimeters per year and with a mean temperature during the warmest month of less than 10 degrees Celsius.

polar front

The region or boundary separating air masses of polar origin from those of tropical or subtropical origin.


The process by which the male sex cells in flowering plants (pollen) are transferred from the male part (anther) to the female part (stigma) of the flower. Pollination leads to fertilization and the creation of new seeds that grow into new plants. Most plants are pollinated by insects looking for nectar in the flower, or by animals or wind.


Presence of matter (gas, liquid, solid) or energy (heat, noise, radiation) whose nature, location, or quantity causes (or has the potential to cause) damage to the condition, health, safety, or welfare of animals, humans, plants, or property. Toxic materials in the environment.


A sedentary and simple aquatic animal form characterized by a more or less fixed base, columnar body, and free end with mouth and tentacles, especially as applied to coelenterates.


A group of individuals of the same species living in the same geographic area.

pore space

Pore space in soil is the volume of space that can be filled with water or air. A large pore space is normally filled with air while smaller pore spaces are primarily filled with water.


A measure of the total pore space in the soil.

positive feedback

A positive feedback in a system is where the effect reinforces the cause. This means that the impact will go on increasing. With climate change, for example, when surface temperature increases, it leads to melting of ice. Water is more absorbent to sunlight than ice. This causes more sunlight to be absorbed by Earth, which further increases the temperature.

potable water

Water that is safe for humans to drink, uncontaminated by bacteria or other disease causing pathogens, or by toxic chemicals.

potential energy

Energy stored in a system of forcefully interacting physical entities.

potential energy

Energy stored within an object due to its position in a force field (as in gravitational potential energy) or because of its structure (as in chemical or nuclear energy).


The rate at which work is done or the rate at which energy is consumed.


The slow, conical motion of the earth's axis of rotation, caused by the gravitational attraction of the sun and moon, and, to a smaller extent, of the planets, on the equatorial bulge of the earth. 12,000 years from now the Northern Hemisphere will experience summer in December and winter in June because the axis of the earth will be pointing at the star Vega instead of its current alignment with the North Star of Polaris.


The change in orientation of the rotational axis of a rotating body.


The part of the hydrologic cycle in which the water vapor in the atmosphere condenses and falls to Earth as rain or snow.

preferential option of care for the poor

The moral principle that people in absolute need of the basic goods of life should be given priority in caregiving.


The protective setting aside of natural resources to prevent damage caused by human activities such as logging, mining, hunting, and fishing.

primary consumer

Organisms that feed on green plants or other autotrophic organisms.

primary producer

Organism (autotroph) at the bottom of a food chain that produces its own food using photosynthesis or chemosynthesis, and is a food source for primary consumers (herbivores).

primary producers

Primary producers, also called autotrophs, are organisms that can produce their own food. Most autotrophs lie at the bottom of the food chain, serving as food sources for animals farther up the line. Primary producers are self-sufficient when it comes to meals: they produce their own food using light, carbon dioxide, water and sometimes other chemicals too.


Remaining in a pure state, without human alteration.


A single-celled organism that lacks a membrane-bound nucleus (karyon), mitochondria, or any other membrane-bound organelle.


Any of a group of complex organic macromolecules that contain carbon, hydrogen, oxygen, nitrogen, and usually sulfur and are composed of one or more chains of amino acids. Proteins are fundamental components of all living cells and include many substances, such as enzymes, hormones, and antibodies, that are necessary for the proper functioning of an organism. They are essential in the diet of animals for the growth and repair of tissue and can be obtained from foods such as meat, fish, eggs, milk, and legumes.


A stable subatomic particle that has a positive electric charge and is part of the nucleus of an atom. Its charge is opposite to that of an electron but is equal in magnitude. A proton's mass is 1,836 times that of an electron.


A phylum or group of phyla that comprises the single-celled microscopic animals, which include amoebas, flagellates, ciliates, sporozoans, and many other forms.


The moral virtue of good decision-making with respect for all circumstances.


A silver to yellow, metallic mineral consisting of iron and sulfur. It is used as a source of iron and in making sulfur dioxide. Because of its shiny look and often yellow color, it is sometimes mistaken for gold and for this reason is also called fool's gold.

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