Advanced study in biology at the graduate level opens the door to a wide range of research and teaching careers. With most Ph.D. programs and some master's programs in biology, the graduate school will waive tuition and offer some kind of stipend in return for working part-time as a research or teaching assistant. Ideally, students interested in graduate study will begin work on choosing a graduate school early in the junior year. Waiting until the fall semester of the senior year may result in fewer choices; and waiting as late as the spring semester of the senior year will certainly close off opportunities (but it may still be possible to get into some schools).
William and Mary has for setting up a strategy and getting started with graduate school application process. Biology Department graduates who attend graduate school will likely take the GRE exam, interview with graduate programs, and apply for pre-doctoral fellowships as part of their continuing higher education.