IB Biology Exam Prep

Category - Biology

Which of the following best describes the role of clonal selection in the development of acquired immunity to a pathogen?
  1. Leukocytes that are stimulated as a result of increased body temperature during an infection differentiate from their precursor stem cells more rapidly.
  2. Lymphocytes that possess receptors that can bind to the pathogen's antigens rapidly divide to produce many cells capable of recognizing and attacking the pathogen.
  3. Natural killer cells that produce antibodies capable of attacking the pathogen are stimulated to produce more antibodies than cells that do not produce such antibodies.
  4. Phagocytes that ingest many pathogens over a short period of time grow and divide more rapidly than those that have not ingested many pathogens.
Explanation
Correct Response: B. Acquired immunity is a specific immune response that is generated after exposure to specific antigens. Each lymphocyte contains receptors that recognize a single antigen. When that specific antigen binds to a receptor on a lymphocyte, the lymphocyte divides to produce many cells capable of recognizing and attacking the pathogen source of the antigen. After the initial stimulation of a lymphocyte, the body can respond more rapidly upon exposure to the same pathogen. Immune responses as a result of increased body temperature (A) and natural killer cells (C) are part of the non-specific immune response, rather than acquired immunity. Although certain phagocytes help trigger clonal selection by presenting antigens to lymphocytes, phagocytes (D) are themselves part of the non-specific immune response, in that they recognize and destroy pathogens indiscriminately.
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