This unit, providing information about human nutrition and energy use, has been prepared for students whose level of thinking is transitional between concrete and formal stages. The unit is based upon an analogy between combustion and respiration and upon the molecular structure of food components. The core portion of the unit presents activities related to the nature of food, digestion and assimilation. The eight options contain suggestions for more detailed student investigation of topics mentioned in the core. The options are: "Testing Foods"; "Measuring the Energy of Food" (Calculation of the energy available, in mega-joule, in common foodstuffs); "Energy for Action" (ATP and muscle contraction); "Enzymes Inside You" (includes investigation of laundry enzymes); "What Happens to the Food We Eat?"; "Respiration without Oxygen" (fermentation); "What is a Balanced Diet?"; and "Why be Fat?. In addition to instruction for activities, the student booklet contains diagnostic tests and annotated answers, a glossary, and food tables. The teacher's guide contains list of necessary apparatus, references, and notes on the objectives and use of the unit. (AL)