This student guide is divided into two sections: "Mice and Men" and "Environmental Balance," and constitutes parts three and four of the first year of the Portland Project, a three-year, integrated high school science curriculum. Part One of the guide deals with topics such as cell, reproduction, embryology, genetics, genetic diseases, genetics and change, populations, effects of density on populations, ecosystems, and communities. Part Two deals with related topics. After studying about ecosystems in general terms, the emphasis is shifted to studying about the harmful effects of human activity in upsetting the balance of ecosystems. Topics include water pollution, air quality, and effects of air pollution. A separate chapter is entitled "Where Do We Go From Here?". In both the parts, laboratory exercises are suggested for each topic and space is provided for recording notes. A lengthy list of supplementary materials (films, periodicals, community organizations, other laboratory manuals, and reference materials) is included. (Related documents are ED 064 093 - ED 064 097.) (PS)