This introductory chapter on the earth's biosphere was authored by Dr. Michael Pidwirny of Okanagan University College. This chapter is one of 10 composing an online educational text titled the Fundamentals of Physical Geography (reported on in the February 20, 2004, NSDL Report for the Physical Sciences). The biosphere sub-chapters include: Biological Classification of Organisms; Concept of Ecological Niche; Biotic Interactions and the Distribution of Species; The Nitrogen Cycle; Trophic Pyramids and Food Webs, and more. The hypertext contains good-quality images, a great study guide complete with a chapter summary, numerous key terms (hyperlinked to definitions in the site's Glossary), and study questions. The site also includes a set of related readings with brief annotations, related internet links, and a weblog for site users.