Term | Definition |
P generation | The name for the true-breeding parents. |
p680 | Reaction center chlorophyll in the photosystem II. |
p700 . | Reaction center cholophyll in the photosystem I |
paracrine signaling | Signal released from a cell has an effect on neighboring cells. |
paralogous genes | Homologous genes that are found in the same genome as a result of gene duplication. |
paraphyletic group | A monophyletic group in which some descendants of the common ancestor have been removed. |
parasitoidism | Insects that lay eggs on or in living host; larvae feed on body of host, eventually killing it. (+/-) |
parasympathetic division | A branch of the autonomic nervous system that maintains normal body functions; it calms the body ever conserves energy. |
parental types | Offspring with a phenotype that matches one of the parental phenotypes. |
passive immunity | Immunity conferred by transferring antibodies from an individual who is immune to a pathogen to another individual. |
passive transport | Transport of a substance across a cell membrane by diffusion. No cell energy required. |
pattern formation | The development of a spatial organization of tissues and organs. |
pedigree | A diagram that shows the occurrence of a genetic trait in several generations of a family. |
peptide bond | Bonds that connect amino acids. |
peptidoglycan | Cell wall of prokaryotes, but NOT ARCHAEA. Made of a sugar polymer and polypeptide. |
per capita death rate | Expected number of deaths in a population in a specified period of time. |
per capita offspring | Average number of offspring produced per individual during a specified period of time. |
Peripheral Nervous System (PNS) | The sensory and motor neurons that connect the CNS to the rest of the body. |
peripheral proteins | The proteins of a membrane that are not embedded in the lipid bilayer; they are appendages loosely bound to the surface of the membrane. |
peroxisome | A microbody containing enzymes that transfer hydrogen from various substrates to oxygen, producing and then degrading hydrogen peroxide. |
petal | A modified leaf of a flowering plant; petals are the often colorful parts of a flower that advertise it to insects and other pollinators. |
phagocytosis | Process in which extensions of cytoplasm surround and engulf large particles and take them into the cell. |
phagocytosis | Process in which extensions of cytoplasm surround and engulf large particles and take them into the cell. |
phenotype | An organism's traits. |
phosphodiester bonds | Bonds between phosphate group and pentose sugar in nucleic acids. |
phosphoralation | Process of adding a phosphate group. |
phosphorylation | The metabolic process of introducing a phosphate group into an organic molecule. |
photoautotrophs | Organisms that use light as a source of energy to synthesize organic substances. |
photoautotrophs | Photosynthetic bacteria. |
photolysis | In the thylakoid membranes of a chloroplast during light-dependant reactions, two molecules of water are split to form oxygen, hydrogen ions, and electrons. |
photomorphogenesis | Effects of light on plant morphology. |
photoperiodism | A physiological response to photoperiod, the relative lengths of night and day. An example of photoperiodism is flowering. |
photosystem | A cluster of pigments embedded into a thylakoid membrane. |
phototropism | Growth of a plant shoot toward or away from light. |
phylogenetic trees | Branching diagrams that depict hypotheses about evolutionary relationships. |
phylogeny | Evolutionary history of a species or group of species. |
phylograms | Diagram in which the length of a branch reflects number of changes in a DNA sequence. |
physical map | A genetic map in which the actual physical distances between genes or other genetic markers are expressed, usually as the number of base pairs along the DNA. |
physiology | Study of the functions an organism performs. |
phytochromes . | A class of light receptors in plants. Mostly absorbing red light, these photoreceptors regulate many plant responses, including seed germination and shade avoidance |
pigments | Molecules that absorb, reflect, or transmit light. |
pilli | Hollow tubes used to move cells or exchange DNA between bacteria by conjunction. |
pinocytosis | A type of endocytosis in which the cell "gulps" droplets of fluid into tiny vesicles. |
pioneer species | The first species that colonize new area, such as lichen and mosses. |
pistil | A single carpel or a group of fused carpels in a flower. |
plasma membrane | The membrane at the boundary of every cell that acts as a selective barrier, thereby regulating the cell's chemical composition. |
plasmid | A small ring of DNA that carries accessory genes separate from those of a bacterial chromosome; also found in some eukaryotes, such as yeast. |
plasmids | Small rings of DNA found naturally in some bacterial cells in addition to the main bacterial chromosome. Can contain genes for antibiotic resistance, or other "contingency" functions. |
plasmolysis | This happens when a cell shrinks inside its cell wall while the cell wall remains intact. |
plasmolyze | When the membrane shrinks away from the cell wall as a result of water loss. |
pluripotent | Able to give rise to multiple, but not all, cell types. |
point mutations | chemical changes in just one base pair of a gene |
polar | Molecule with partial charges. Mixes with water. |
pollen tube | A tube that forms after germination of the pollen grain and that functions in the delivery of sperm to the ovule. |
poly-A tail | Modified end of the 3' end of an mRNA molecule consisting of the addition of some 50 to 250 adenine nucleotides. |
polyandry | One female, several males. |
polygamous | An individual of one sex mating with several of the other. |
polygenic inheritance | An additive effect of two or more genes on a single phenotypic character. |
polygyny | One male, several females. |
polymerase chain reaction (PCR) | A technique for amplifying DNA in vitro by incubating with special primers, DNA polymerase molecules, and nucleotides. |
polyphyletic group | A taxonomic grouping consisting of several species that lack a common ancestor (more work is needed to uncover species that tie them together into a monophyletic clade). |
polyploidy | In plants, the result of an extra set of chromosomes during cell division. |
polyribosomes | Strings of ribosomes that work together to translate a RNA message. |
population | Group of individuals of the same species living in the same area. |
population density | The size of the population within a particular unit of space. |
population genetics | Study of allele frequency distribution and change under the influence of evolutionary processes |
positional information | The molecular cues that control pattern formation. |
positive feedback | A type of regulation that responds to a change in conditions by initiating responses that will amplify the change. Takes organism away from a steady state. |
postsynaptic cell | The neuron, muscle, or gland cell that receives the signal from a neuron. |
postzygotic barriers | Barriers that prevent the hybrid zygote from becoming a fertile adult. |
potential energy | Occurs when an object is not moving, but may still posses energy. |
potential range | An area where an organism could potentially survive and reproduce. |
PR protein | A protein involved in plant responses to pathogens (PR = pathogenesis-related). |
pressure potential | This measurement has a minimum value of 0 (when the solution is open to the environment); it increases as pressure increases. |
presynaptic cell | The transmitting neuron in a synapse. |
prezygotic barriers | Barriers that impede mating or hinder fertilization. |
primary consumer | Herbivore. |
primary electron acceptor | Specialized molecule that shares a reaction center with the chlorophyll a molecule in the light reaction. traps high energy electron before it can return to ground state in the chlorophyll. |
primary immune response | Immune response the first time the body is exposed to a particular antigen. Does not peak until 10-17 days after exposure. |
primary production | Amount of light energy converted to chemical energy by autotrophs. |
primary structure | Chain of amino acids. |
primary succession | Succession that begins in a virtually lifeless area. |
primary transcript | The initial mRNA transcript that is transcribed from a protein coding gene. Also called pre-mRNA. |
primase | An enzyme that joins RNA nucleotides to make the primer using the parental DNA strand as a template. |
producer | Autotroph. |
production efficiency | The fraction of energy stored in food that was not used for cell respiration. |
promiscuous | No strong pair bonds or lasting relationships. |
promoter | A specific nucleotide sequence in DNA that binds RNA polymerase and indicates where to start transcribing mRNA. |
prophage | A phage genome that has been inserted into a specific site on the bacterial chromosome. |
prostaglandins | Modified fatty acids that are produced by a wide range of cells. |
proteasomes | A giant protein complex that recognizes and destroys proteins tagged for elimination by the small protein ubiquitin. |
protein kinase | The enzyme that transfers phosphate groups from ATP to protein. |
protein phosphatases | Enzymes that can rapidly remove phosphate groups from proteins. |
protobionts | Aggregates of abiotically produced molecules surrounded by a membrane. |
proton pump | An electrogenic pump that works largely with H+ ions. |
proton-motive force | Emphasizes the capacity of the gradient to preform work. |
provirus | Viral DNA that inserts into a host genome. |
proximate questions | Address environmental stimuli, genetic, physiological, and anatomical causes of a behavior. |
punctuated equilibrium | A model of evolution in which a new species will change the most as it buds from a parent species, and then will change little for the rest of its existence. |
Punnett square | A diagram for predicting the allele composition of offspring from a cross between individuals of known genetic makeup. |
purines | Bases with a double-ring structure. |
pyramid of energy | 90% of all energy is lost between trophic levels. |
pyramids of biomass | Each on this pyramid tier represents standing crop. |
pyramids of numbers | Number of organisms at each trophic level. |
pyrimidines | Bases with a single-ring structure. |
quantitative characteristics | Characteristics that vary along a continuum, usually due to influence of two or more genes. |
quantitative characters | Characters that vary in the population along a continuum (in gradations). |
quaternary consumer | Carnivore that eats tertiary consumers. |
quaternary structure | Results from two or more polypeptide subunits. |
R plasmid | A bacterial plasmid carrying genes that confer resistance to certain antibiotics. |
r-selected species | Life history traits maximize reproductive success in uncrowded environments. Many small offspring that mature quickly, little if any parental care. |
radicle | An embryonic root of a plant. |
radioisotopes | Isotopes that have unstable nuclei and undergo radioactive decay. |
radiometric dating | Dating using decay of radioactive isotopes. |
random dispersion | Random spacing of individuals of the same species within an area. |
reaction center | The location of the first light driven chemical reaction of photosynthesis. |
reading frame | Reading mRNA nucleotides in the correct groupings. |
realized niche | The niche species actually occupies. |
receptacle | The base of a flower; the part of the stem that is the site of attachment of the floral organs. |
reception | The target cell's detection of a signal molecule coming from outside the cell. |
receptor tyrosine kinase | A receptor with enzymatic activity that can trigger more than one signal transduction pathway at once, helping the cell regulate and coordinate many aspects of cell growth and reproduction. |
receptor-mediated | A type of endocytosis in which the cell acquires bulk quantities of specific substances, even though they may not be very concentrated in the extracellular fluid. |
recessive allele | An allele that is masked when a dominant allele is present |
recombinant chromosomes | Chromosomes that carry genes from each parent. |
recombinant DNA | A DNA molecule made in vitro with segments from different sources. |
recombinant types | Offspring who have inherited new combinations of genes and have phenotypes that don't match either parental phenotypes. |
recticular formation | Registers and controls activity level, increases excitement, and helps generate sleep. |
redox reactions | When there is a transfer of one or more electrons from one reactant to another. |
reduced hybrid fertility | Sterile hybrids due to uneven chromosome number. |
reduced hybrid viability | When the genes of different species interact and impair hybrid development. |
reducing agent | Donates electrons and becomes oxidized. |
reduction | Gain of electrons. |
regulator | An animal that uses internal control mechanisms to moderate internal change in the face of external fluctuation. |
regulatory gene | A gene that codes for a protein, such as a repressor, that controls the transcription of another gene or group of genes. |
relative abundance | The proportion of each species. |
relative fitness | Fitness of a particular genotype. |
repeated reproduction | Species that reproduce over and over. |
replication fork | A Y-shaped region on a replicating DNA molecule where new strands are growing. |
repolarization | Return of the cell to resting state, caused by reentry of potassium into the cell while sodium exits the cell. |
repressor | A protein that suppresses the transcription of a gene. |
reproductive cloning | Using a somatic cell from a multicellular organism to make one or more genetically identical individuals. |
reproductive isolation | Barriers that impede members of two different species fro producing fertile offspring. |
reproductive rate | Difference between per capita birth and per capita death rates. |
reproductive rates | Study of females to determine reproductive output and how it varies with age of female. |
reproductive table (fertility schedule) | Age-specific summary of reproductive rates in a population. |
resource partitioning | Differentiation of niches that enables similar species to coexist. |
response | The transduced signal finally triggers a specific cellular response. |
resting potential | The membrane potential of a neuron that is at rest. |
restoration ecology | Applies ecological principles in an effort to return degraded ecosystems to conditions as similar as possible to their natural state. |
restriction enzyme | A degradative enzyme that recognizes and cuts up DNA (including that of certain phages) that is foreign to a bacterium. |
restriction fragment | The fragment of DNA that is produced by cleaving DNA with a restriction enzyme. |
restriction fragment length polymorphisms (RFLPs) | differences in the restriction sites on homologous chromosomes that result in different restriction fragment patterns. |
restriction point | A point of no return in the cell cycle; once this point passes, a cell is committed to a full round of the cell cycle. |
restriction site | A specific sequence on a DNA strand that is recognized as a cut siteby a restriction enzyme. |
reticular fibers | Fibers made of collagen fibers that are very thin and branched. Forma tightly woven fabric that joins connective tissue to adjacent tissues. |
retrovirus | An RNA virus that reproduces by transcribing its RNA into DNA and then inserting the DNA into a cellular chromosome; an important class of cancer-causing viruses. |
reverse transcriptase | An enzyme encoded by some certain viruses (retroviruses) that uses RNA as a template for DNA synthesis. |