Why does each paragraph need a topic or title for it?

What is the the story about in the movie freedom writers be very detailed.

In a series of experiments, hershey and chase radioactively labeled dna and protein in viruses and then used labeled viruses to infect bacteria. hershey and chase's experiments definitively showed that a. dna and not protein is the genetic material. b. dna and protein work together as a cell's genetic material. c. protein and not dna is the genetic material. d. neither dna nor protein act as a cell's genetic material

Read this passage: "your being dramatic," said eliza. "i don't think its dramatic to say that your going to fail the humanities class if you don't pass it's final exam," replied her mother. which revision corrects the misspelled words in the passage?