This is one of 30 lessons from the NSTA Press book Scientific Argumentation in Biology. The lesson engages students in an argumentation cycle in which they evaluate three alternative claims regarding whether and how plants use oxygen to obtain energy. The lesson engages students by discussing how animals use sugar to obtain energy and then opens the comparison between animals and plants. Students are guided to design and carry out an investigation that will allow them to collect evidence needed to construct an argument defending one of the three claims. As they construct this argument, students build and apply knowledge of photosynthesis, respiration, energy and matter transfers within ecosystems, and interactions among organisms and their environments. This lesson is intended for middle or high school students. Teachers are encouraged to refer to the preface, introduction, student assessment samples, and appendix provided in the full book for important background on the practice of argumentation and resources for classroom implementation.