ve charges. The presence of polar covalent bonds allows other polar molecules to surround molecule: example: glucose sugar in water.

pollen grains  The containers for male gametophytes of seed plants produced in a microsporangium by meiosis. Microspores produced by seed plants that contain the male gametophyte. PICTURE

pollen tube Structure produced by the tube nucleus in the pollen grain through which the sperm nucleus (or nuclei in angiosperms) proceed to travel through to reach the egg. PICTURE

pollination The transfer of pollen from the anthers to the stigma by a pollinating agent such as wind, insects, birds, bats, or in a few cases the opening of the flower itself.

polygenic inheritance  Occurs when a trait is controlled by several gene pairs; usually results in continuous variation. PICTURE

polymer Organic molecule composed of smaller units known as monomers. A large molecule composed of smaller subunits, for example starch is a polymer of glucose, proteins are polymers of amino acids.

polymerase chain reaction (PCR)  A method of amplifying or copying DNA fragments that is faster than cloning. The fragments are combined with DNA polymerase, nucleotides, and other components to form a mixture in which the DNA is cyclically amplified.

polynucleotides  Long chains of nucleotides formed by chemical links between the sugar and phosphate groups.

polyp  The sessile form of life history in cnidarians; e.g., the freshwater hydra.

polyploidy  Abnormal variation in the number of chromosome sets. The condition when a cell or organism has more than the customary two sets of chromosomes. This is an especially effective speciation mechanism in plants since the extra chromosomes will establish reproductive isolation with the parental population(s), an essential for speciation. PICTURE 1 | PICTURE 2

polysaccharides  Long chains of monosaccharide units bonded together; e.g., glycogen, starch, and cellulose. PICTURE

pons  The region that, with the medulla oblongata, makes up the hindbrain, which controls heart rate, constriction and dilation of blood vessels, respiration, and digestion. PICTURE

population  A group of individuals of the same species living in the same area at the same time and sharing a common gene pool. A group of potentially interbreeding organisms in a geographic area.

population dynamics  The study of the factors that affect the growth,