During lectures and on slides, key points of a presentation should be made very clear, perhaps with the addition of stars, underlines or bolding.  Often, one leaves a lecture without ever really knowing which key points the lecturer was hoping to emphasize.  Biology is already a very difficult subject in terms of the volume of material to be memorized.  Even those who have been in the field for many decades still cannot know every minute detail by heart.  Expecting that of the students seems a bit ridiculous to me.

For instance, after a professor declares during the very first lecture of a series that students should understand principles, not details.  And, they then proceed to ask a question about a single slide in 280 slide series of lectures one must ask, why the misleading preface for the course, and second, how is this testing my overall knowledge of the subject matter?