These are the ideas that I hope a student will remember say seven years after the end of a course. The processes and actions of life are products of its basis in the physical nature of matter and energy. Structure and function are complexly and predictably correlated. Unifying characters such as the genetic code suggest a common ancestry for all living things. Life adjusts to short term change through negative feedback and homeostatic regulation which expend energy to mainain internal conditions within survivable limits.
Living systems can heal minor or brief damage or injury.
I agree with Dave McNeely - the evolutionary thesis makes sense of it all. When I teach intro, I start with the definition of science, then the definition of life, which leads me directly to what we know and hypothesize about life's origins. The course ends up as a kind of narrative, which I continually go back to to set a context for introducing new groups and their defining characteristics. As for other themes like diseases or pollution, those are great themes for individual lectures or groups of lectures. I think each lecture should have a thesis too, as well as a well-defined beginning, middle, and end.