I would recommend 'Life: the Science of Biology' by Sadava Heller Orians Purves and Hillis. Absolutely massive book, starts with basic chemistry, goes on to biochemistry, then cell biology, and gradually works its way up in scale through ecology. http://bcs.whfreeman.com/thelifewire8e/default.asp has notes from all the chapters, interactive diagrams, and some interactive quizzes.