IGCSE Biology Paper-4: Specimen Questions with Answers 278 - 279 of 279

Passage

Heroin abuse may lead to HIV infection. There is currently no approved vaccine that prevents the spread of HIV. Vaccination stimulates active immunity against specific pathogens.

Question 278 (1 of 2 Based on Passage)

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Explain what is meant by passive immunity.

Explanation

Immunity that develops after a person receives immune system components, most commonly antibodies, from another person. Passive immunity can occur naturally, such as when an infant receives a mother՚s antibodies through the placenta or breast milk, or artificially, such as when a person receives antibodies in the form of an injection (gamma globulin injection) . Passive immunity provides immediate protection against an antigen, but does not provide long-lasting protection.

Question 279 (2 of 2 Based on Passage)

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Explain how vaccination stimulates active immunity.

Explanation

A vaccine can confer active immunity against a specific harmful agent by stimulating the immune system to attack the agent. Once stimulated by a vaccine, the antibody-producing cells, called B cells (or B lymphocytes) , remain sensitized and ready to respond to the agent should it ever gain entry to the body. A vaccine may also confer passive immunity by providing antibodies or lymphocytes already made by an animal or human donor. Vaccines are usually administered by injection (parenteral administration) , but some are given orally or even nasally (in the case of flu vaccine) . Vaccines applied to mucosal surfaces, such as those lining the gut or nasal passages, seem to stimulate a greater antibody response and may be the most effective route of administration.