Question

Identify the three stages of immunity.

Answer 1

The Immune System has 3 Lines of Defense Against Foreign Pathogens:
Physical and chemical barriers form the first line of defense when the body is invaded.

1. Physical and Chemical Barriers (Innate Immunity)
2. Nonspecific Resistance (Innate Immunity)
3. Specific Resistance (Acquired Immunity)
Physical Barriers
The skin has thick layer of dead cells in the epidermis which provides a physical barrier. Periodic shedding of the epidermis removes microbes.   
Chemical Barriers
Lysozyme, an enzyme produced in tears, perspiration, and saliva can break down cell walls and thus acts as an antibiotic (kills bacteria)

Nonspecific Resistance (Innate Immunity)

The second line of defense is nonspecific resistance that destroys invaders in a generalized way without targeting specific individuals:
Specific Resistance (Acquired Immunity)
The third line of defense is specific resistance. This system relies on antigens, which are specific substances found in foreign microbes.