We present a simple, effective, and inexpensive spectrophotometer design that may be used in a stand-alone teaching module, and to enhance various unit operations experiments. The spectrophotometers described performed as well as a commercial option at estimating cell concentration in a bioreactor and tracking a first-order reaction. Such devices have been found to be ideal for hands-on classroom demonstrations of reaction kinetics, for use in our unit operations lab, and as tools for community outreach.