Is it in my mind or on the page?

I finished up a short essay earlier today for my school application. After I was done it suggested by the parent-folks that I put in a bibliography. I didn't cite or quote anything in the essay, and the entire thing was written off the top of my head (simple question about the differences between image production in motion-picture film and television/video). In my communications theory class last semester, I grilled the TA about this same concern: at what point is something coming out of my head and when is it cited? Now, quotations are obviously cited. Something that you read yesterday so you could write the essay is cited. But what about something i read four months ago on my own? It's not like I was born being able to infer the mechanics of television, so I had to read it all somewhere at some time, but when does it become my knowledge? Due to the complexity of the information I present, I'm going to create a bibliography from some of the websites I frequent, because they've apparently had a running problem with plagiarism at the school, and I'd like to play it safe because I want to get accepted.