I have taken many classes on-line and usually you do the coursework at your own pace. Sometimes the classes require you to find a local proctor to supervise your exams, which local library's can often provide. Speaking for myself, attempting to take all four science classes concurrently in an on-line setting seems like a potential recipe for disaster. I had a difficult enough time taking Chemistry and Physics in a live classroom. If you have brilliant math skills, you may be OK. It's always nice to have people to bounce ideas off of and to ask questions when you encounter difficult subject matter, which is not always easy in an on-line environment. Good luck!!