On-Line Biology Book: GLOSSARY W X Y Z white blood cell Component of the blood that functions in the immune system. Also known as a leukocyte. wood The inner layer of the stems of woody plants; composed of xylem. X-chromosome One of the sex chromo
On-Line Biology Book: GLOSSARY All contents 1992, 1994, 1995, 1997, 1998, 1999, M.J. Farabee, all rights reserved. V vaccination The process of protecting against infectious disease by introducing into the body a vaccine that stimulates a primary im
On-Line Biology Book: GLOSSARY U umbilical cord The structure that connects the placenta and the embryo; contains the umbilical arteries and the umbilical vein. unicellular Single-celled. uniformitarianism The idea that geological processes have r
On-Line Biology Book: GLOSSARY S S phase That period of interphase when new DNA is synthesized as part of replication of the chromatin . PICTURE salivary amylase An enzyme secreted by the salivary glands that begins the breakdown of complex sugars
On-Line Biology Book: GLOSSARY R race A subdivision of a species that is capable of interbreeding with other members of the species. radially symmetrical In animals, refers to organisms with their body parts arranged around a central axis. Such ani
On-Line Biology Book: GLOSSARY P Q pacemaker. See sinoatrial node . Pacinian corpuscles Sensory receptors located deep in the epidermis that detect pressure and vibration. paleontology The study of ancient life by collection and analysis of fossil
On-Line Biology Book: GLOSSARY O occipital lobe The lobe of the cerebral cortex located at the rear of the head; is responsible for receiving and processing visual information. PICTURE oils Triglycerides that are liquid at room temperature. oncoge
On-Line Biology Book: GLOSSARY M macroevolution The combination of events associated with the origin, diversification, extinction , and interactions of organisms which produced the species that currently inhabit the Earth. Large scale evolutionary c
