Describe the concept of immunity.

Description should include

• definition of immunity
• the immune system and its function
• types of immunity, including differentiation between passive and active immunity
• the methods for acquiring immunity. 

Process/Skill Questions:

• What is an antigen?
• What is an antibody?
• What events could cause an animal to have a weakened immune system?
• Why is immunity to certain diseases so important for animals?