What discovery is attributed to Elie Metchnikoff?

Correct Answer: B

Rationale: The correct answer is B: Phagocytosis. Elie Metchnikoff is credited with discovering phagocytosis, the process in which certain cells engulf and digest foreign particles or microorganisms. He observed this phenomenon in starfish larvae, leading to a groundbreaking understanding of how immune cells defend the body against pathogens. Choice A (Antitoxins) is incorrect because although Metchnikoff made contributions to immunology, his notable discovery was phagocytosis, not antitoxins. Choice C (Germ theory of disease) is incorrect as this theory was developed by Louis Pasteur and Robert Koch. Choice D (Smallpox eradication) is incorrect as this achievement is primarily attributed to the efforts of Edward Jenner and the World Health Organization.

Correct Answer: B

Rationale: Correct Answer: B Rationale: 1. Innate immunity is the first line of defense and does not have memory. 2. Memory is a characteristic of adaptive immunity, not innate immunity. 3. Adaptive immunity improves responses over time through memory. 4. Innate immunity is always present, functional, non-specific, and responds immediately. Summary: A: Always present and functional - Correct, innate immunity is always ready. B: Has memory to improve responses over time - Incorrect, innate immunity lacks memory. C: Recognizes pathogens in a non-specific manner - Correct, innate immunity is non-specific. D: Can respond immediately - Correct, innate immunity acts rapidly.

Correct Answer: B

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.

Correct Answer: B

Rationale: The correct answer is B (C3a, C4a, and C5a) because these complement components are known as anaphylatoxins that mediate inflammation by inducing vasodilation, increasing vascular permeability, and recruiting immune cells. C3b (choice A) is involved in opsonization, not inflammation. C5b (choice C) is part of the membrane attack complex for cell lysis. C1q (choice D) initiates the classical complement pathway, but it does not directly mediate inflammation.

Correct Answer: C

Rationale: Step 1: Innate immunity is the body's first line of defense against pathogens. Step 2: Physical defenses include barriers like skin and mucous membranes. Step 3: Cellular defenses include immune cells like macrophages and natural killer cells. Step 4: These defenses are present from birth and do not require prior exposure to pathogens. Step 5: Choice C is true as innate immunity encompasses both physical and cellular defenses, making it the correct answer. Other choices are incorrect: A: Innate immunity does play a role in stimulating adaptive immunity through antigen presentation. B: It does not require prior exposure to function, as it is a rapid and non-specific response. D: Innate immunity is not antigen-specific; adaptive immunity is responsible for antigen-specific responses.