Dynamic visualizations have the potential to make abstract scientific phenomena more accessible and visible to students, but they can also be confusing and difficult to comprehend. This research investigates how dynamic visualizations, compared to static illustrations, can support middle school students in developing an integrated understanding of energy in photosynthesis. Two hundred 7th-grade students were randomly assigned to either a dynamic or a static condition and completed a web-based inquiry unit that encourages students to make connections among energy concepts in photosynthesis. While working on the inquiry unit, students in the dynamic condition interacted with a dynamic visualization of energy transformation, whereas students in the static condition interacted with a series of static illustrations of the same concept. The results showed that students in both conditions added new, scientific ideas about energy transformation and developed a more coherent understanding of energy in photosynthesis. However, when comparing the two conditions, we found a significant advantage of dynamic visualization over static illustrations. Students in the dynamic condition were significantly more successful in articulating the process of energy transformation in the context of chemical reactions during photosynthesis. Students in the dynamic condition also demonstrated a more integrated understanding of energy in photosynthesis by linking their ideas about energy transformation to other energy ideas and observable phenomena of photosynthesis than those students in the static condition. This study, consistent with other research, shows that dynamic visualizations can more effectively improve students' understanding of abstract concepts of molecular processes than static illustrations. The results of this study also suggest that with appropriate instructional support, such as making predictions and distinguishing among ideas, both dynamic visualizations and static illustrations can benefit students. This study underscores the importance of curriculum design in ensuring that dynamic visualizations add value to science instructional materials. (Contains 3 figures, 7 tables and 1 note.)