A pathogenic bacterium has been engulfed by a phagocytic cell as part of the innate immune response. Which of the following illustrations best represents the response? [source: AP Biology Course and Exam Description Fall 2012, p. 132]
How do natural killer cells react to healthy cells compared to cells infected with a pathogen?
  1. Natural killer cells recognize MHC I on a healthy cell and do not kill it, while the infected cells

Why does the human body need more than its skin to function as a barrier to infecting pathogens?
  1. Skin works only against some types of bacteria. To prevent the entry of other pathogens, other physical or chemical barriers are needed.
  2. Skin does not provide a broad coverage against invasion of the body by any foreign particle, so it is not a very effective barrier.
  3. Pathogens could enter the body through several places that are not covered by skin that need to have

What is the mechanism that skin uses to protect against diseases caused by organisms?
  1. high pH
  2. mucus
  3. tears
  4. desiccation
How does the human body use a chemical barrier as part of the innate immune response?
  1. Mucus secretions trap and rinse pathogens out of the body.
  2. Urination carries pathogens out of the urinary tract.
  3. Low pH conditions in the stomach kill some pathogens and prevent other pathogens from growing.
  4. Cilia in the nasal