Innate and Adaptive Immunity Questions and Answers

Answer: D

The phenomenon is herd immunity.

When most of a population is immune, through infection or vaccination, a pathogen finds too few susceptible hosts to keep spreading, so even the people who are not immune are indirectly protected. That population-level protection is herd (community) immunity.

Innate immunity is the non-specific first defence every individual has from birth. Adaptive immunity is the specific response of lymphocytes and antibodies within one person. Active immunity is adaptive immunity a person develops after their own exposure or vaccination. All three describe protection inside an individual, not the reduced risk to susceptible people in an immune population.

Answer: A

Phagocytosis was first described by Elie Metchnikoff.

In the 1880s Metchnikoff observed mobile cells in starfish larvae engulfing foreign particles, and went on to show that white blood cells engulf and digest bacteria. He named the process phagocytosis and founded the cellular theory of immunity, sharing the 1908 Nobel Prize with Paul Ehrlich.

Ehrlich championed the humoral (antibody) side of immunity. Robert Hooke described cells in cork in 1665, and Robert Koch established the germ theory of disease with his postulates; neither described phagocytosis.

Answer: A

The match is P-(ii); Q-(iii); R-(iv); S-(i).

• Active acquired immunity develops when the body itself meets a pathogen (or a vaccine) and mounts its own response: direct contact with pathogens that enter the body.
• The first line of defence is the surface barriers: skin, mucous membranes and their secretions.
• Passive natural immunity is the transfer of maternal antibodies across the placenta (or in milk).
• The second line of defence is the internal innate response, including complement proteins and interferons, along with phagocytes and inflammation.

The other options confuse the placental transfer with active immunity or put complement in the first line of defence.

Answer: B

The pairing is Peak I - IgM; Peak II - IgG.

Peak I is the primary response, after the first exposure: it is small and appears after a lag, and its antibody is mainly IgM, the first class made by naive B cells. During that response B cells undergo class switching and form memory cells.

Peak II is the secondary response. Memory B cells respond quickly to the second exposure and produce a much larger and longer-lasting titre, made up mainly of high-affinity IgG.

IgG first and IgM second reverses the order of class switching. IgE is the antibody of allergy and anti-parasite responses, not of the primary response to a bacterium. IgG for both peaks ignores the IgM that dominates a primary response.