Included in the unit are ideas related to: categorizing (classifying), quantifying, model making, and developing terminology. Laboratory experiences include activities to investigate: similarities and differences, making and using keys, the relative nature of measurement, making a physical model of an atom, models for probability (heredity), and changes in language. These laboratory experiences are inquiry-oriented, although designed to contribute to the development of understanding how a scientist behaves toward his world. The format for each laboratory experience is as follows: Introduction, Materials and Equipment, Collecting Data, and Follow-up. (BR)