Incorporating Problem-Based Learning into high school Biology can be difficult, but here's a fully developed PBL unit that gets students interested by centering the unit around a problem relevant to them: Should energy drinks be regulated?
This unit includes a complete unit plan using the template provided by the Buck Institute, student materials for the inquiry lab and Socratic seminar, detailed rubrics for the lab report and Socratic seminar, and tips for teachers that I've found helpful after doing this unit the past few years. I've also included slides that I've used to help students focus in on how to design the lab. The slides include sample pictures that will assist both students and teacher. Another item that I've found useful and included is sample data that previous students have collected that you can use in any way you would like.
Whether you've never done PBL or have been using it for years, this unit can be adjusted to any experience level. In fact, I've adjusted how much we do in this unit every year depending on the students I have.
This unit is centered on diffusion and osmosis, but can be an easy springboard into homeostasis and systems such as the excretory and circulatory systems.
I hope you and your students enjoy this unit as much as we have!