A picture book about photosynthesis that is easily understood and holds your interest? Believe it. Living Sunlight combines the talents of Molly Bang and Penny Chisholm to present a narrative, told from the sun's point of view, about how photosynthesis is the "most important process on Earth."
There are several things that I like about this book. The text explains the process of plants making food in a way that is easily understood. Blues, greens, and yellows dominate the vivid illustrations which include inserts that show photosynthesis up close. While the main text is meant for a primary audience, the author's notes in the back make for a great science lesson for third graders and above.
The authors have provided a great teacher's guide for K-2 and 3-5 students which includes an excellent selection of links for teaching science. I would also recommend taking the main text and turning it into a reader's theater script with several narrators. The author's notes, with subheadings, would make for good mini-lessons on nonfiction text features and main ideas.