The purpose of this study is to present an activity designed according to inquiry-based science approach and its implementation. The activity set up towards guided inquiry and was performed with participating 12 preservice science teachers and 24 eighth grade students. The activity started with a daily-life problem related to Yozgat Çamlik National Park. First, envelopes, presented as hidden documents signed by park chief, and a research kit were provided to learners. Then a nature trip was organized to identify species of plants listed in the distributed inventory. Learners expressed the problem (the national park's bio-diversity is decreasing) as a result of interpreting the data collected in a nature trip. Learners were asked to form hypotheses about factors effecting bio-diversity and determine investigation methods to test their hypotheses. At final, learners reported the results and research processes. The activity can be used both in science and biology courses.