Biology teachers will be able to use some of these content-rich, pre-made lectures but should probably give the videos a quick preview. Some of the videos will fit right in with your curriculum, while others won't be the right fit for every student. The (sometimes) slow pace and handwritten screens could cause some students' eyes to glaze over. However, some of the videos here, especially those on evolution and genetics, could work as solid stand-ins for kids who miss class or simply want a review resource. Other topics -- for example, the details in the photosynthesis unit -- go beyond a typical high school level; these might work as an extension for more advanced students but won't help everyone.
Without the tasks and quizzes that accompany Khan's math videos, you'll need to supply kids with learning content that goes beyond just sitting and watching. Of course, it's great if students watch ahead of time, on their own; this way, class can be focused on questions, points of confusion, and activities that support learning. If using a flipped model, have your students make outlines, take Cornell Notes, or answer teacher-made questions to help them stay focused. You could even have your students use a shared Google doc to compile the class's collective understanding.