Lewis/Life - Glossary

P

pacemaker Specialized cells in the wall of the right atrium that set the pace of the heartbeat. 720

Pacinian corpuscle pah-SIN-ee-en KOR-pus-el A receptor in the skin that senses touch. 656

paleontology PAY-lee-on-TOL-ah-gee Study of evidence of past life. 390

palisade mesophyll cells PAL-eh-sade MEZ-o-fil SELZ Columnar cells along the upper side of a leaf specialized for light absorption. 543

pancreas PAN-kree-ass A structure that has an endocrine part that produces somatostatin, insulin, and glucagon and a digestive part that produces pancreatic juice. 672, 764

parapodia par-a-PODE-ee-a Pairs of fleshy appendages that polychaete worms use to locomote. 521

parasitism par-a-si-tizm A symbiotic relationship in which one member harms the other. 435

parasympathetic nervous system PAR-ah-SIM-pah-THET-ik NER-vus SIS-tum Part of the autonomic nervous system that controls vital functions such as respiration and heart rate when at rest. 622

parathyroid glands par-ah-THY-roid GLANZ Four small groups of cells behind the thyroid gland that regulate calcium level in blood and tissue fluid, by secreting parathyroid hormone. 663

parenchyma pah-REN-kah-mah Abundant, unspecialized plant cells that can divide. 535

parental generation (P1) The first generation in a genetic cross. 265

parsimony analysis PAR-si-mone-ee eh-NAL-eh-sis A statistical method to identify the most realistic evolutionary tree based on molecular data. 399

parthenogenesis par-tho-GEN-eh-sis Female reproduction without fertilization. 192

parturition par-ter-I-shun The birth of a baby. 216

passive immunity Immunity generated when an organism receives antibodies from another organism. 798

pedicellariae ped-ee-SELL-ar-ay Echinoderm pincers. 524

pedigree PED-eh-gree A chart showing relationships of relatives and which ones have a particular trait. 268

pelagic zone pah-LA-gik zone Water above the ocean floor. 883

penis PEE-nis Male sex organ. 197

pentaradial symmetry pent-a-RAY-de-al SIM-it-ree A body form with five arms, characteristic of echinoderms. 524

pepsin PEP-sin A stomach enzyme that chemically digests protein. 760

peptide bond PEP-tide BOND A chemical bond between two amino acids resulting from dehydration synthesis. 48

peptide hormone PEP-tide HOR-moan A hormone composed of amino acids that is water soluble but fat insoluble so that it cannot traverse a cell membrane. 662

pericardium per-ee-KAR-de-um Connective tissue sac that houses the heart. 718

pericycle PEAR-ee-si-kel A ring of parenchyma cells in a root's cortex that produces branch roots that burst through the cortex and epidermis into the soil. 548

periderm PEAR-ee-derm Outer covering of mature stems and roots. 541

period Time period within an era. 359

periodic table peer-ee-OD-ic TA-ble Chart that lists naturally occurring elements according to their properties. 32

peripheral nervous system per-RIF-er-al NER-vous SIS-tum (PNS) Neurons that transmit information to and from the central nervous system. 618

periplast PER-ee-plast A supportive protein structure on the inside face of the cell membrane of euglenoids. 466

peristalsis pear-ee-STAL-sis Waves of muscle contraction that propel food along the digestive tract. 759

peritubular capillaries pear-ee-TOOB-yu-lar CAP-eh-LAIR-eez Capillaries that surround renal tubules in kidney nephrons. 780

permafrost PER-mah-frost Permanently frozen part of the ground in the tundra. 878

peroxisome per-OX-eh-soam A membrane-bounded sac that buds from the smooth ER and that houses enzymes important in oxygen use. 72

petal PET-al Large and often vibrant flower part that may lure pollinators. 563

petiole PET-ee-ol The stalklike part of a leaf. 541

phagocytic vacuole fag-o-sit-ik VAK-u-ole A space that forms within a protozoan cell when it engulfs food particles. 459

pharyngeal gill slits farr-in-GEE-al GILL slitz Chordate structures that function in feeding or respiration. 525

pharynx FAHR-inx The throat. 736

phelloderm FEL-ah-derm Living parenchyma cells in secondary growth in plants. 552

phenocopy FEEN-o-kop-ee An environmentally caused trait that resembles an inherited trait. 276

phenotype FEEN-o-type Observable expression of a genotype. 265

phenotypic ratio feen-o-TIP-ik RAY-shee-o Proportions of different phenotypes among offspring of a genetic cross. 266

pheromones FER-eh-moanz Biochemicals an organism secretes that elicit a response in another member of the species. 660

phloem FLOW-m Plant vessels that transport photosynthetic products. 496, 534

phospholipid FOS-fo-LIP-id A molecule consisting of a lipid and a phosphate that is hydrophobic at one end and hydrophilic at the other end. 85

phosphorylation foss-for-eh-LAY-shun Adding a phosphate (PO4) group to a molecule. 119

photochemical smog fo-to-KEM-i-kal SMOG A form of air pollution caused by vehicle emissions. 892

photon FOE-ton A packet of light energy. 111, 147

photonasty FO-toe-nas-tee A nastic response in plants to light and dark. 582

photoperiodism fo-toe-PER-ee-o-diz-um A plant's ability to measure seasonal changes by the length of day and night. 583

photophosphorylation FO-toe-FOS-for-eh-LAY-shun A photosynthetic reaction in which energy released by the electron transport chain linking the two photosystems is stored in the high-energy phosphate bonds of ATP. 155

photoreactivation fo-to-re-ac-ti-VAY-shun A type of DNA repair in which an enzyme uses light energy to break pyrimidine dimers. 319

photoreception fo-toe-ree-CEP-shun Detecting light by means of pigment molecules in contact with sensitive membranes. 644

photorespiration fo-to-res-per-A-shun A process that counters photosynthesis. 160

photosynthesis FO-toe-SIN-the-sis The series of biochemical reactions that enable plants to harness sunlight energy to manufacture nutrient molecules. 73, 146

photosystem FO-toe-SIS-tum A cluster of pigment molecules that enables green plants to absorb, transport, and harness solar energy. 153, 154

phototroph FO-toe-trofe An organism that derives energy from the sun. 445

phototropism fo-toe-TROP-iz-um A plant's growth towards unidirectional light. 578

pH scale A measurement of how acidic or basic a solution is. 41

phycobilins fi-ko-BILL-ins Pigments of red algae. 469

phylogenies fi-LODJ-ah-nees Evolutionary relationships between species. 390

phylum FI-lum A major taxonomic group, just beneath kingdoms. 12

phytochrome FI-toe-krome A pale blue plant pigment that promotes flowering of long-day plants and inhibits flowering of short-day plants. 585

phytoplankton FITE-o-PLANK-tun Microscopic algae. 458

pili pill-I Short projections on bacterial cells used to attach to objects. 446

pinacocytes pine-AK-o-sites Cells in the body wall of a sponge. 515

pineal gland pie-NE-al GLAND A small oval structure in the brain that produces melatonin, a hormone that senses light and dark periods. 675

pinocytosis pine-o-si-TOE-sis A protozoan cell pinches inward and brings fluid into the cell. 459

pioneer species pie-o-NEER SPEE-sheez The first species to appear in an area devoid of life. 856

pistil PIS-til The female reproductive structures and their coverings in a flower. 563

pith PITH Ground storage tissue in the center of the stem in plants that have concentric cylinders of xylem and phloem. 541

pituitary gland pah-TU-eh-tare-ee GLAND A pea-sized gland in the human head that releases several types of hormones. 666

placebo pla-SEE-bo An inert substance used as an experimental control. 25

placenta pla-CEN-tah A specialized organ that connects a pregnant female placental mammal to unborn offspring. 216

plankton PLANK-tun Microscopic organisms that drift in large populations in water. 458

Plantae Plan-tay The plant kingdom. 14, 429

plasma PLAZ-ma A watery, protein-rich fluid that forms the matrix of blood. 594, 711

plasma cells PLAZ-mah SELZ Mature B cells that secrete large quantities of a single antibody type. 795

plasmodium plaz-MO-dee-um A multinucleated mass of an acellular slime mold. 470

plastid PLAS-tid A plant organelle that encapsulates photosynthetic membranes. 151

platelet PLATE-let A cell fragment that is part of the blood and orchestrates clotting. 595, 714

Platyhelminthes plat-ee-hel-MEN-theez Flatworms. 510, 517

pleiotropic PLY-o-TRO-pik A genotype with multiple expressions. 276

plumule PLU-mule The epicotyl plus the first leaves of a young plantlet. 568

pluripotency plur-e-POE-ten-see A cell that retains the potential to specialize in any way. 210

pneumatophore new-MAT-o-for The floating portion of a cnidarian. 517, 550

point mutation POYNT mu-TAY-shun A change in a single DNA base. 341

polar body A small cell generated during female meiosis, enabling cytoplasm to be partitioned into just one of the four meiotic products, the ovum. 204

polar covalent bond PO-lar co-VAY-lent BOND A covalent bond in which electrons are attracted more toward one atom's nucleus than to the other. 38

polar nuclei PO-lar NU-klee-i The two nuclei in a cell of a plant's megagametophyte. 567

pollen grains Male microgametophytes. 560

pollen sacs The four microsporangia in an anther, the male part of a flower. 563

pollination Transfer of pollen from an anther to a receptive stigma. 567

polyandry pol-ee-AN-dree A mating system in which one female mates with several males. 830

polychaetes POL-ee-ketes Marine segmented worms. 521

polygamy pol-IG-ah-mee A mating system in which a member of one sex associates with several members of the opposite sex. 830

polygenic pol-ee-JEAN-ik A trait caused by more than one gene. 276

polygynandry POL-ee-gine-AN-dree Communal mating displays, involving several males and several females. 830

polygyny pol-IJ-ah-nee A mating system in which one male mates with several females. 830

polymer POL-eh-mer A long molecule composed of similar subunits. 43

polyp POL-ip The sessile form of a cnidarian. 517

polypeptide chain pol-ee-PEP-tide CHAYN A long polymer of amino acids. 46

polyploidy POL-ee-PLOID-ee A cell with extra chromosome sets. 297, 414

polyunsaturated (fat) POL-ee-un-SAT-yer-a-tid FAT A fatty acid with more than one double bond. 45

pons PONZ An oval mass in the brain stem where white matter connects the medulla to higher brain structures and gray matter helps control respiration. 627

population A group of interbreeding organisms living in the same area. 9, 404

population bottleneck A type of genetic drift. An event kills many members of a population, and a small number of individuals restore its numbers, restricting the gene pool. 409

population density The abundance of species per unit area or volume of habitat. 838

population dispersion The pattern in which individuals are scattered throughout the habitat. 838

Porifera pore-IF-er-a Sponges. 510, 515

positive feedback A biochemical pathway in which accumulation of a product stimulates its further production. 123, 664

postsynaptic cell post-sin-AP-tik SEL One of two adjacent neurons that receives a message. 617

potential energy The energy stored in the position of matter. 112

preembryonic stage pre-em-bree-ON-ik STAYJ Prenatal development before the organism folds into layers. 216

preformation pre-for-MAY-shun The idea that a gamete or fertilized ovum contains an entire preformed organism. 210

presynaptic cell PRE-sin-AP-tik SEL One of two adjacent neurons that transmits a message. 616

primary consumers Animals that eat plants and form the second trophic level. 862

primary growth Lengthening of a plant due to cell division in the apical meristems. 534

primary immune response The immune system's response to its first encounter with a foreign antigen. 795

primary nutrient deficiency Too little of a particular nutrient due to inadequate diet. 757

primary oocyte PRI-mare-ee OO-site An intermediate in ovum formation. 204

primary producers The species forming the base of a food web or the first link in a food chain. 859

primary spermatocyte PRI-mare-ee spur-MAT-o-site An intermediate in sperm formation. 204

primary (1_) structure The amino acid sequence of a protein. 49

primary succession Appearance of life in an area previously devoid of life. 856

primitive streak PRIM-eh-tiv STREEK The pigmented band along the back of a 3-week embryo that develops into the notochord. 226

principle of competitive exclusion The idea that two or more species that compete for the same limited resources cannot indefinitely occupy the same habitat. 845

principle of superposition The idea that lower rock layers are older than those above them. 376

prions PRI-onz Infectious protein particles. 77

product rule The chance of two events occurring equals the product of the chances of either event occurring. 271

profundal zone pro-FUN-dal ZONE The deep region of a lake or pond where light does not penetrate. 879

progenotes pro-JEAN-notes Collections of nucleic acid and protein that were forerunners to cells. 357

progesterone pro-JES-ter-own A hormone produced by the ovaries that controls secretion patterns of other reproductive hormones. 674

proglottids pro-GLOT-ids Structures in tapeworms that contain reproductive structures. 518

prokaryotic cell pro-CARE-ee-OT-ik SEL A cell that lacks organelles. Bacteria and cyanobacteria. 14, 63

prolactin pro-LAK-tin A hormone made in the anterior pituitary gland that stimulates milk production. 667

promoter pro-MOW-ter A control sequence near the start of a gene that attracts RNA polymerase and transcription factors. 327

pronuclei pro-NU-kle-eye The genetic packages of gametes. 218

prophase PRO-faze The first stage of cell division, when chromosomes condense and become visible. 171

prophase I PRO-faze I Prophase of meiosis I, when synapsis and crossing-over occur. 198

prophase II PRO-faze II Prophase of the second meiotic division. 201

prostaglandins pros-tah-GLAN-dinz Lipids released locally and transiently at the site of a cellular disturbance. 660

prostate gland PROS-tate GLAND A small gland that produces a milky, alkaline fluid that activates sperm. 197, 675

protein PRO-teen A polymer of amino acids. 46

Protista pro-TEES-ta The kingdom that includes unicellular, eukaryotic organisms, the protista. 14, 429

proton PRO-ton A particle in an atom's nucleus carrying a positive charge and having one mass unit. 32

protonephridia pro-toe-nef-RID-ee-a Structures in flatworms that help maintain internal water balance. 518

protoplasm PRO-tow-plaz-m Living matter. 60

protostomes PRO-toe-stomes One of two coelomate lineages, characterized by spiral cleavage, a blastopore that develops into a mouth, and determinate cleavage. 512

protozoa PRO-toe-ZO-a Single-celled eukaryotes often classified by their mode of movement, including amoebae, euglenae, and paramecia. 458

proximal convoluted tubule PROX-eh-mel kon-vo-lu-tid TUBE-yule Region of the nephron, proximal to the glomerular capsule, where selective reabsorption of useful components of the glomerular filtrate occurs. 783

pseudocoel su-doe-SEEL The fluid-filled hydrostatic skeleton of a roundworm. 519

pseudocoelomate su-doe-SEEL-o-mayt An animal that retains a body cavity from an early embryonic stage, but one that is not lined with mesoderm. 511

pseudoplasmodium su-doe-plaz-MO-dee-um The multicellular, mobile stage of the life cycle of a cellular slime mold. 471

pseudopod su-doe-pod The portion of an amoeba that extends outward, moving the organism. 459, 692

pseudostratified epithelium su-doe-STRAT-if-eyed ep-eh-THEEL-e-um A single layer of epithelium whose nuclei are at different levels, giving the appearance of more than one layer. 594

pulmonary artery PULL-mo-nair-ee AR-ter-ee The artery that leads from the right ventricle to the lungs. 720

pulmonary semilunar valve PULL-mo-nair-ee SEM-ee-LOON-er VALVE The valve that leads from the right ventricle to the pulmonary artery. 720

pulmonary veins PULL-mo-nair-ee VAYNZ Four veins that lead from the lungs to the left atrium. 720

pulp The soft inner part of a tooth, consisting of connective tissue, blood vessels, and nerves. 760

punctuated equilibrium PUNK-chew-ate-ed ee-kwa-LIB-ree-um The view that life's history has had periods of little change interrupted by bursts of rapid change. 415

pupil The opening in the iris that admits light into the human eye. 266, 648

purine PURE-een A type of organic molecule with a double ring structure, including the nitrogenous bases adenine and guanine. 313

Purkinje fibers per-KIN-gee FI-berz Muscle fibers that branch from the atrioventricular node and transmit electrical stimulation rapidly in the heart. 722

pyramid of biomass An ecological pyramid depicting weight of organisms at each trophic level. 863

pyramid of numbers An ecological pyramid depicting number of organisms at each trophic level. 863

pyrenoid PIE-re-noyd A starch-containing large chloroplast in a green alga. 465

pyrimidine pie-RIM-eh-deen A type of organic molecule with a single ring structure, including the nitrogenous bases cytosine, thymine, and uracil. 313

pyruvic acid pi-ROO-vic AS-id The products of glycolysis. 131

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