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parable: an illustrative story that uses common events and culture to convey a meaning or lesson.

parasite: an organism which lives and feeds on or within another host organism without benefit.

pathogen: a disease-causing organism.

pathogenic strain: a line of organisms that carry disease.

pathological: indicative of or caused by a disease or condition.

pathologist: a physician who specializes in diagnosis and classification of diseases by laboratory tests such as examination of tissue and cells under a microscope.

pesticides: chemical substances (e.g., an insecticide or fungicide) that kill harmful organisms and are used to control pests, such as insects, weeds or microorganisms.

pesticides: chemicals that kill or inhibit the growth of organisms that people consider undesirable. Fungicides (which kill fungi), herbicides (which kill plants) and insecticides (which kill insects) are types of pesticides.

pH: a measure of a substance's acidity or alkalinity. The term pH translates literally to pondus hydrogenii, which means "potential hydrogen." The terminology refers to acidity being due to a predominance of hydrogen ions in a water-containing solution.

phosphorus: an element in the periodic table with the symbol P and atomic number 15 that plays an essential role in the tissues of both plants and animals including animal bones. Uses include fertilizers, explosives, fireworks, pesticides, toothpaste and detergents.

photosynthesis: the process by which green plants, algae and other organisms that contain chlorophyll use sunlight to produce carbohydrates (food). Oxygen is released as a byproduct of photosynthesis.

phycologist: someone who studies algae.

physician: someone qualified by education and legally authorized to practice medicine.

physiologist: a biologist specializing in the processes and functions of an organism.

phytoplankton: tiny, free-floating, photosynthetic organisms in aquatic systems including diatoms and dinoflagellates.

plankton: a broad group of aquatic organisms unable to swim against ocean currents (although capable of swimming vertically up and down in the water). See phytoplankton and zooplankton for examples.

plankton net: a net that captures any living being that drifts. Plankton nets can have a wide variety of mesh sizes that filter organism size for collection.

poaching: hunting, trapping or fishing illegally.

point source pollution: the opposite of non-point source pollution. Pollution that comes from a single source and that may be traced back to a single source, such as a pipe.

pollination: the process by which pollen is transferred from the male part of a flower to the female part of the same or another plant. Insects, birds, mammals and other creatures, as well as wind or water, can all pollinate plants.

Porcupine River caribou: the population of Arctic caribou that live along the Porcupine River in Northern Alaska and Yukon and whose numbers have been dropping in recent years, in part, due to climate change.

post-consumer waste: waste, often used in manufacturing, that originates from things consumers have used.

pre-consumer waste: waste created during manufacturing that is recovered for use. For example, scraps and roll-ends left over after a batch of paper is made at a paper mill are considered to be pre-consumer waste.

predator: an animal that hunts and kills other animals for its food.

prey: an organism hunted and eaten by a predator.

primal: original, primitive; fundamental; first in importance.

primeval: ancient, aboriginal, having existed from the beginning; in an earliest or original stage or state.

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