Dr. Paul's Virtually Biology Show.
Radial symmetry. A body plan in which the body parts originate from the central of the organism like spokes in a wheel. Star fish and jellyfish and among the creatures which share this type of symmetry.
Recessive allele. An alternate form of a gene that has no obvious effect on the phenotype of a heterozygous individual.
Recombination. A name given for one of any number of processes in prokaryotes and eukaryotes that serve to produce new combinations of genetic material already existing in individuals. Thus crossing over and independent assortment would be examples of recombination in meiosis. Sexual reproduction as a whole is a type of recombination.
Reduction. The addition of electrons and often hydrogen ions to a substance. Contrast oxidation.
Reflex. An automatic response to a stimulus consisting usually of a small number of steps, perhaps just a muscle twitch. A motor program as an elaborate sequence of automatic responses is become a common term. However, the distinction is not always clear cut.
Releaser. A general term for a stimulus that triggers a fixed action pattern.
Reproductive success. Just as it sounds this term refers to the number of offspring an organism has. This is not the same as fitness which is reproductive success relative to the other members of the population.
Ribosomal RNA. The RNA found as part of the ribosome and that serve in part as a ribozyme involved in forming peptide bonds.
Ribozyme. An RNA molecule that serves as an enzyme. The Ribosomal RNA in the ribosome acts as an enzyme to catalyze the formation of peptide bonds during protein synthesis
RuBP. Ribulose bi phosphate. A five carbon sugar with two phosphate groups that is the starting material for the Calvin cycle. Carbon dioxide is attached to this compound to form a six carbon unstable intermediate which breaks into two three carbon molecules of PGA.
Rough endoplasmic reticulum(Rough ER). A network of membranous sacs connected to the nuclear envelope that is covered with ribosomes. Rough ER is a site for active synthesis and collection of proteins.