Which of the following best describes it example of a specific internal response to harmful bacteria 1) skin serves as a physical barrier that prevents bacterial from entering the body. 2) saliva contains enzymes that destroy bacteria and prevents infection. 3) bacterial infection causes the release of histamine, which leads to inflation and swelling. 4) antigens trigger the production of antibodies, which mark bacteria for destruction.

The hershey and chase experiments involved the preparation of two different types of radioactively labeled phage. which of the following best explains why two preparations were required? a. the bacteriophage used in the experiments was a t2 phage. b. it was necessary that each of the two phage components, dna and protein, be identifiable upon recovery at the end of the experiment. c. each scientist had his own method for labeling phage, so each conducted the same experiment using a different isotope. d. establishing the identity of the genetic material required observation of two phage generations.