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Immunity: Question 8

Syllabus 11.2

Multiple choice AS 1 mark

A person bitten by a venomous snake is given an injection of antivenom. The antivenom contains antibodies against the snake's venom that were produced in the blood of another animal, such as a horse, and then extracted and purified for medical use.

Which type of immunity does the bitten person gain from this injection?

Choose an answer to check it, then compare with the worked solution below.
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Worked solution

Step 1: Decide between active and passive

Active immunity is gained when a person’s own immune system produces antibodies (usually with the formation of memory cells), while passive immunity is gained when a person simply receives ready-made antibodies produced by another organism. In this scenario, the antibodies against the venom were made in another animal’s blood, not by the patient’s own B-lymphocytes. The patient is therefore gaining passive immunity.

Step 2: Decide between natural and artificial

Natural immunity is gained through a normal life process, such as catching an infection or, in the case of a baby, receiving antibodies through the placenta or breast milk. Artificial immunity is gained through a deliberate medical intervention, such as a vaccination or an injection of antibodies. Here, the antivenom is given by a doctor as a medical treatment after the bite, so this is artificial immunity, even though the antibodies themselves originally came from a living animal.

Step 3: Combine the two classifications

Putting these together, the bitten person gains passive artificial immunity: passive because the antibodies were made by another organism and simply transferred to the patient, and artificial because this transfer happened through medical treatment rather than a natural process.

Step 4: Evaluate each option

  • A: incorrect. The antibodies were not produced by the patient’s own immune system, so this is not active immunity.
  • B: incorrect. Again, this is not active immunity, since the patient did not make the antibodies themselves.
  • C: incorrect, although passive is correct, receiving a medical injection is an artificial process, not a natural one.
  • D: correct, the patient receives ready-made antibodies (passive) via a deliberate medical injection (artificial).

Final answer

  • The person gains passive artificial immunity from the antivenom injection, option D.