Suitable for high school and above, this four-volume reference provides a broad introduction to many facets of biology, and concentrates in depth on a smaller number of central ideas and phenomena that are central to all biological processes. The 432 entries also discuss the history of the science, explore related fields, critical issues such as embryogenesis and commercial applications of biological research, and ethical issues. One of the major themes is molecular genetics, from genes and chromosomes to cloning and the Human Genome Project. Other topics include human physiology; comparative animal and plant physiology; health issues important to students such as smoking, alcohol, and sexually transmitted diseases; animal and plant diversity, and major environmental challenges. Entries range in length from a few paragraphs to several pages and contain suggestions for further reading. Other features include definitions, color illustrations, and glossaries and topic outlines in each volume.