Elaborating on Jenner's observations, who is considered to have created the first "attenuated" vaccine

Correct Answer: A

Rationale: The correct answer is A: Louis Pasteur. He is considered to have created the first "attenuated" vaccine based on his work with the rabies vaccine in the 1880s. Pasteur's method involved weakening the virus to make it less harmful while still eliciting an immune response. Other choices are incorrect because: B: Robert Koch is known for his contributions to microbiology and germ theory, not for creating the first attenuated vaccine. C: Ilya Metchnikoff is known for his work on immunology and phagocytosis, not for developing the first attenuated vaccine. D: Adolf Von Behring is known for his research on diphtheria antitoxin, not for creating the first attenuated vaccine.

Correct Answer: B

Rationale: Macrophages differentiate in tissues because they originate from monocytes which leave the bloodstream and mature into macrophages in various tissues. This process is essential for their diverse functions in immune response and tissue maintenance. Choices A, C, and D are incorrect because macrophages do not differentiate from blood neutrophils, the common lymphoid progenitor, or in the bone marrow.

Correct Answer: A

Rationale: The correct answer is A because naïve lymphocytes circulate through blood, enter lymph nodes (LN) via high endothelial venules (HEV), encounter antigens in LN, exit via efferent lymphatics, drain into the thoracic duct, and return to blood circulation. Choice B is incorrect because it skips the step of entering LN through HEV. Choice C is incorrect because it starts with inflammatory sites instead of blood, and it also lacks the step of entering LN through HEV. Choice D is incorrect as only option A correctly follows the sequential order of recirculation of naïve lymphocytes.

Correct Answer: D

Rationale: The correct answer is D because auxin hormones play a crucial role in promoting seedling elongation (A), are transported downward through a plant (B), and affect cell elongation in roots at lower concentrations (C). Auxins are known for their ability to stimulate cell growth and elongation, which is essential for seedling growth. They are also transported in a polar manner from the shoot tip downwards, influencing various plant processes along the way. Additionally, auxins regulate root growth by promoting cell elongation at lower concentrations. Therefore, all the statements (A, B, and C) are supported by the functions of auxin hormones, making option D the correct choice.

Correct Answer: B

Rationale: The correct answer is B: to vaccination. Acquired immunity is the immune response developed after exposure to a vaccine, which stimulates the immune system to recognize and remember specific pathogens. Vaccination helps the body build immunity without causing serious illness like choice A, without requiring repeated exposure like choice C, and without being related to treatment with penicillin like choice D. Vaccination mimics natural infection, prompting the body to produce memory cells that can respond more effectively when encountering the actual pathogen in the future.