Using microfluidic channels for in vivo experiments in biology reduces the dimensions of an experiment to a cellular scale. This increases precision in the spatiotemporal control of chemical signals applied to a cell membrane which is crucial in quantifying resulting changes in the conformation and distribution of membrane and intracellular proteins. We have designed microfluidic experiments to study chemotaxis in the amoeba Dictyostelium discoideum. In a natural environment, these cells use chemical signaling to begin starvation-induced aggregation. Cells generate a complex pattern of cyclic adenosine monophosphate (cAMP) that drives their migration toward a self-organized central point. To better determine which aspects of a gradient trigger a chemotactic response, we used several microfluidic channels in which local cAMP concentration can be precisely manipulated by controlling flow through the device. We also used high-precision photolysis of molecularly caged cAMP to generate dynamic gradients that could be controlled on subsecond timescales. This led to observation of a number of different cellular mechanisms for turning in a changing gradient and established the necessity for statistical measurements of turning behavior under different conditions. This process was initiated with collection of data from four different stages in cell development that quantified how the tendency to maintain polarization increases with development time.