We present an inquiry-based, hands-on laboratory exercise on enzyme activity for an introductory college biology course for science majors. We measure student performance on a series of objective and subjective questions before and after completion of this exercise; we also measure performance of a similar cohort of students before and after completion of an existing, standard, "direct" exercise over the same topics. Although student performance on these questions increased significantly after completion of the inquiry exercise, it did not increase after completion of the control, standard exercise. Pressure to "cover" many complex topics as preparation for high-stakes examinations such as the Medical College Admissions Test may account for persistence of highly efficient, yet dubiously effective "cookbook" laboratory exercises in many science classes. (Contains 4 tables.)