Why is Edward Jenner's experiment on a young boy considered a scientific landmark?

Correct Answer: D

Rationale: Step 1: Jenner observed milkmaids were protected from smallpox due to prior exposure to cowpox. Step 2: Jenner decided to inoculate a young boy with cowpox first. Step 3: Jenner then inoculated the boy with smallpox to test immunity. Step 4: The boy did not contract smallpox, demonstrating immunity. Step 5: Conclusion: Jenner proved cowpox exposure can make individuals immune to smallpox. Other choices are incorrect: A: The boy never contracted smallpox, not just because of the mild form of smallpox in the milkmaid. B: Inoculating with virulent smallpox first would not demonstrate cowpox immunity. C: Jenner did not just substitute cowpox for smallpox; he specifically tested immunity by exposing the boy to both viruses.

Correct Answer: B

Rationale: The correct answer is B because IL-8 is a chemokine that specifically functions to recruit neutrophils to the site of infection. Neutrophils are crucial for fighting off pathogens. A: Increase of adhesion molecules on local endothelial cells is not directly induced by IL-8. C: Systemic effects, including fever, are typically mediated by other cytokines like IL-1 and IL-6. D: Increase of acute-phase proteins is not the primary role of IL-8 in the immune response.

Correct Answer: C

Rationale: Rationale: Afferent lymphatic vessels transport lymph containing antigens from tissues to lymph nodes (LN). Option C is correct because afferent lymphatics do not transport antigens directly from the blood to LN. Other choices are incorrect because afferent lymphatics enter LN at multiple sites (B), transport antigens from tissues to LN (A), and connect tissues to secondary lymphoid organs (D).

Correct Answer: A

Rationale: The correct answer is A: plants response to stimulation. Tropism refers to the growth or movement of an organism in response to a stimulus. Plants exhibit tropisms such as phototropism (response to light) and geotropism (response to gravity). This choice accurately defines the phenomenon. Choice B is incorrect because reducing lateral branching is not a defining characteristic of tropism. Choice C is incorrect because the length of day and night does not directly relate to tropism. Choice D is incorrect because not all options listed are characteristics of tropism.

Correct Answer: D

Rationale: The correct answer is D because neurons are specialized cells that carry signals, making them the functional units of the nervous system. Neurons consist of a cell body, dendrites, and axons, fulfilling the criteria mentioned in options A, B, and C. Therefore, option D encompasses all the essential characteristics of neurons, making it the correct choice. Options A, B, and C individually do not fully capture the comprehensive nature of neurons, as they only cover specific aspects of what neurons are, whereas option D encompasses all the correct statements regarding neurons.