Developing T cells in the thymus can express

Correct Answer: A

Rationale: The correct answer is A because developing T cells initially express both CD4 and CD8 co-receptors in the thymus. This stage is crucial for T cell maturation and selection. Eventually, T cells undergo positive and negative selection processes to become either CD4+ helper T cells or CD8+ cytotoxic T cells based on their specificity and function. Choices B and C are incorrect because T cells initially express both CD4 and CD8. Choice D is also incorrect as T cells do express either CD4 or CD8 during their development in the thymus.

Correct Answer: B

Rationale: The correct answer is B: Infectious diseases. The immune system's main function is to protect the body from foreign invaders such as bacteria, viruses, and parasites. It recognizes and eliminates these pathogens to prevent infections. Autoimmune diseases (A) occur when the immune system mistakenly attacks healthy cells. Neurological disorders (C) and cardiovascular diseases (D) are not primarily defended against by the immune system as they are not caused by external pathogens.

Correct Answer: C

Rationale: The correct answer is C because adaptive immunity involves T and B lymphocytes that provide specific immune responses tailored to particular pathogens. T and B lymphocytes are key players in adaptive immunity, recognizing and targeting specific antigens. Choice A is incorrect because macrophages are part of innate immunity. Choice B is incorrect because innate immunity is nonspecific and immediate, while adaptive immunity is specific and takes time to develop. Choice D is incorrect because physical barriers are a characteristic of innate immunity, not adaptive immunity.

Correct Answer: C

Rationale: The correct answer is C: Identifying and eliminating abnormal cells. This function is most relevant to cancer because the immune system's ability to recognize and destroy abnormal cells is crucial in preventing the development and spread of cancer. The immune system constantly surveys the body for cells that have mutated or become cancerous, and when identified, it initiates an immune response to eliminate them. This process is essential for maintaining the body's health and preventing cancerous cells from proliferating. Choice A (Suppressing cytokine release) is incorrect because cytokines play a role in regulating the immune response, which can be important in cancer immunity. Choice B (Promoting adaptive immunity only) is incorrect as both innate and adaptive immune responses are involved in combating cancer. Choice D (Limiting the effectiveness of phagocytes) is incorrect as phagocytes are important in recognizing and destroying cancer cells.

Correct Answer: A

Rationale: Step 1: Selective genetic pressure refers to the process where specific genetic traits are favored due to environmental factors. Step 2: Rroma populations and their genetic response to Yersinia pestis demonstrate selective genetic pressure as they have developed genetic adaptations to resist the plague bacterium. Step 3: This adaptation is a result of prolonged exposure to the pathogen, leading to the survival and reproduction of individuals with genetic variations that confer resistance. Step 4: Other choices are incorrect because mutation rates in viruses like the flu (B) do not necessarily involve genetic pressure, increased pathogen diversity in unvaccinated populations (C) is a consequence of lack of immunity, and non-specific activation of innate immunity (D) is not a selective process based on genetic traits.