We describe the use of Euglena gracilis for student-designed investigations of environmental factors that affect population growth of this unicellular flagellate. Each group of students can choose a topic of interest to them, but within the confines of a simple cell culture system that requires little space for each student group, and at a fairly low cost. Students are provided with stock cultures of E. gracilis, along with detailed instructions on preparing control medium and counting cells using a hemocytometer. Students then design their own experiments to test factors that possibly affect population growth over several weeks.