.::Dictionary Entries P::.

Dictionary Entries P

Pahoehoe: Hawaiian name for a fast moving, liquid type of lava.

Palmate: In plants, a term referring to a leaf which has leaflets originating at one point, like the palm of a hand.

Image can be found at LEAF SHAPE II.

Parallax: The apparent shift of an object when looked at from different angles. An example of parallax can be found by looking at an object with one eye closed, then looking at it again using the other eye. The object will seem to have shifted, because the angle between your eyes has changed.

Parasite: The exploitive organism in a symbiotic relationship, which takes from its host, and returns nothing. A parasitic organism can also be harmful to its host.

Parent element: In radioactive decay, the element that is decaying. For example, in the decay of ²³⁸U to ²⁰⁶Pb, ²³⁸U is the parent element.

Parsec: An astronomical unit of measurement equal to 3.262 light years, or about 3.086*10¹⁶ meters. Astronomers get this number by measuring a when a stars parallax is one arcsecond.

Partial Veil: The tissue covering young gills of some fungi; as the cap expands this tissue breaks and leaves remnants in a ring around the stipe or cap margins.

Peptide: Any molecule that can hydrolyze into amino acids and form into the basis for proteins.

Perennial: Referring to any herbaceous plant that lives longer than two years.

Peristalsis: Term used to describe a wave-like motion of muscles that form a hollow tube. This motion is generally used to transport materials from one part of the tube to another, with an example being the esophagus, which employs peristalsis to transport food from the mouth to the stomach.

Petal: In flowers, the sometimes colored, scented portion that protects the reproductive organs. Can often be brightly colored and scented to help attract animals.

Petiole: The stalk of a leaf.

pH: Meaning literally "Per Hydrogen." Refers to the amount of concentrated hydrogen a substance has. Water, being neutral, has a pH level of 7. Substances with a pH level less than 7 are said to be acids, while those with more than 7 are said to be alkaloids.

Phloem: A system in plants where sugars and other substances are transported.

Phosphate group: Term referring to a grouping of phosphorous atoms bonded to four different oxygen atoms, which are themselves attached to a larger molecule.

Photoautotrophic: An organism that makes its own food by means of photosynthesis.

Photosynthesis: The process by which green plants, algae, and some bacteria combine sunlight, carbon dioxide (CO₂), and water (H₂O) to form carbohydrates and oxygen (O₂).

Phylum: A taxonomic division that is above class and below kingdom.

Pigment: Any molecule that absorbs light and in turn reflects a particular color in the tissue the molecule is part of.

Pistil: In flowering plants, it is the female portion of a flower, which consists of one or more carpels.

Placenta: A structure that forms on the uterine wall, that provides a developing organism with food nutrients, and also can act as waste disposal.

Plant: A kingdom that primarily consists of immobile, eukaryotic, mostly photoautotrophic organisms.

Plate: In geology, any of several areas of the lithosphere that move about on the mantle. Sometimes these plates correspond to continents.

This image can be found at Lecture#1.

Plate tectonic theory: In geology, a theory that holds that the Earths crust is made up of many plates, all of which are moving over the liquid mantle. This theory is a unifying concept, in that it explains many different geological features, such as volcanoes, volcanic island arcs, and certain types of mountain ranges.

This image, along with more information about plate tectonics, can be found at the following website: A slice through the Earth: plate tectonic processes.

Pollen: The microspore used by seed plants for reproduction.

Polymer: Any large molecule that is composed of smaller molecules.

Polypeptide chain: An organic compound with a sequence of three or more amino acids. Peptide bonds between them result in a regular pattern of nitrogen atoms in the carbon backbone: -N-C-C-N-C-C-. Every protein consists of one or more polypeptide chains.

Polyploid: An organism that has at least three sets of haploid chromosomes, or multiple sets of diploid chromosomes. Polyploidy can happen in a few different ways. One form happens when an organism is reproducing

Polysaccharide: A polymer made up of monosaccharides connected by glycosidic bonds. Well known polysaccharides include: starch, glycogen, and cellulose.

Pons: Portion of the brain between the midbrain and the medulla oblongata.

Posterior: The rearward facing portion of an object or organism. Compare with anterior.

Precocial: A term that refers to animals that are partially independent soon after birth.

Process: In anatomy, a term that refers to a bony projection, which is usually an attachment point for a muscle system.

Protein: An organic compound made up of one or more polypeptide chains.

Protein Synthesis: The process by which proteins are made.

Proton: A component of an atoms nucleus that has a positive charge, and provides mass.

Purine: A nucleotide base that has a double ring structure, as seen in the picture to the right. Examples of purines include adenine and guanine.

Pyrimidine: A nucleotide base that has a single ring structure, as seen to the image to the right. Examples of pyrimidines include cytosine and thymine.