Despite our best teaching efforts, many students hold misconceptions related to the roles plants play in gas-related processes (Amir and Tamir 1994; Hershey 1992; 2004). In an effort to remedy this problem, the author presents a series of activities that address common plant-related gas-process misconceptions held by middle school students. The instructional sequence starts with students speculating about the fate of a plant sealed in a clear jar (terrarium) and then making observations for several months to determine the accuracy of their speculations. (Contains 3 figures.)