Discovering concepts through observation, exploration, and constructing scientific explanations of phenomena is best practice in science education. Instead of following lab procedures to verify a known answer or solution, involve students in the work of science. Begin by presenting a phenomenon to engage students in scientific inquiry and uncover their prior knowledge. Curiosity spurs questions driving investigations to explore hypotheses in search of explanations of the phenomenon. This paper describes how engaging in the science practices enables students to explore and explain why marshmallows either shrink or puff up in a dynamic environment containing a closed and open system.