MCAT Biology Question 112: Answer and Explanation

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Question: 112

7. Which of the following is true regarding passive and active immunity?

  • A. Active immunity requires weeks to build, whereas passive immunity is acquired immediately.
  • B. Active immunity is short-lived, whereas passive immunity is long-lived.
  • C. Active immunity may be acquired during pregnancy through the placenta.
  • D. Passive immunity may be acquired through vaccination.

Correct Answer: A

Explanation:

Active immunity refers to the production of antibodies during an immune response. Active immunity may be conferred by vaccination, such as when an individual is injected with a weakened, inactive, or related form of a particular antigen that stimulates the immune system to produce antibodies. Active immunity may require weeks to build. Passive immunity, on the other hand, involves the transfer of antibodies either passively or by injection. An example would be during pregnancy, when some maternal antibodies cross the placenta and enter fetal circulation, conferring passive immunity to the fetus. Although passive immunity is acquired immediately, it is very short-lived, lasting only as long as the antibodies circulate in blood.

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