1. Distinguish between humoral and cell-mediated immunity, identifying the cells involved, their origin, and their functions.

2. Describe the clonal selection theory, and explain how it accounts for the ability to defend against subsequent exposure to a particular antigen.

3. Active immunizations involve the exposure of a person to a pathogen whose virulence (ability to cause disease) has been reduced without altering its antigenicity (nature of its antigens). How do you think this might be accomplished? What are the benefits and dangers of this procedure?

4. Passive immunizations involve injecting a person exposed to a pathogen with serum containing antibodies, called antiserum or antitoxin. Antiserum is developed by injecting an animal with a pathogen. What happens in that animal? What are the benefits and shortcomings of passive immmunizations compared to active immunization?