How are important conditions or changes in the environment received and transduced by organisms? We will examine the molecular and cellular bases of the transduction and encoding of physical phenomena such as light, sound, and chemicals in a variety of organisms, including plants and invertebrates. We will focus on questions such as: What properties of the physical world are sensed (and which ones are ignored)? What mechanisms are used to convert physical or chemical energy into a changed biological state within a cell? What are the consequences of this changed state? How are differences in the attributes of one modality in the physical world represented by differences in molecular and cellular processes? Among the examples we will consider are: a comparison of visual structures and pigments in bacteria, plants, arthropods, molluscs, and primates; sound transduction and its musical consequences; and the olfactory system of mammals - which is able to produce a large variety of receptors specific to an individual's experience. Format: lecture/discussion/laboratory, averaging 4 1/2 hours per week. Evaluation will be based on examinations, a paper, and a project proposal. Prerequisite: Biology 205. Enrollment limit: 32 (expected: 24). Preference to seniors, then to Biology majors.