This five-chapter document (part of a series on biology and human welfare) focuses on biological systems as energy sources and on the teaching of this subject area. Chapter 1 discusses various topics related to energy and ecology, including biomass, photosynthesis and world energy balances, energy flow through ecosystems, and others. Chapter 2 discusses the importance and reactions of photosynthesis. Chapter 3 examines various aspects of biofuels, including methane (biogas production, advantages and disadvantages of anaerobic biogas generators, biogas economics, and others). Chapter 4 offers a curriculum guide for teaching about biological systems as energy sources. It shows how the teaching of this subject area fits the aims of secondary school science education; offers suggestions for developing and implementing curricula which incorporate topics on biological systems as energy sources; and presents (in chart format) environmental aspects of biological education, listing concepts, principles, and/or topics with related practical experiences, teaching strategies, and values/skills fostered. Chapter 5 offers and describes various teaching and learning strategies, including descriptions of three student activities (such as making a model biogas generator). A list of references and resources is included. (JN)