Scientific investigations play a vital role in teaching and learning the process of science. An investigative task that was developed for pre-university students is described here. The task involves extraction of an enzyme from a vegetable source and its detection by biochemical method. At the beginning of the experiment, a hypothesis is presented to the students. The students are then asked to design an experiment to test the validity of this hypothesis. While performing the investigation, students' conceptual understanding, basic experimentation skills and cognitive abilities are tested.