Book excerpt: Incorporating the new terms and research compiled in the last few years in this field, The Facts On File Dictionary of Biology, Fourth Edition clearly defines the basic principles and terms used in this widely studied branch of science. Approximately 300 new entries have been added to reflect new information, and current entries and back matter have been revised as needed. Pronuciation symbols have been added, and many photographs have been replaced. Pairing rich content with an accessible format, this science dictionary is ideal for high school and college classrooms and libraries, and will be useful to specialists and laypeople alike.