Peripheral nervous system (PNS)

Correct Answer: D

Rationale: Step-by-step rationale: 1. The Peripheral Nervous System (PNS) includes nerves and ganglia, making choice B correct. 2. PNS is located outside the Central Nervous System (CNS), supporting choice A. 3. Since both A and B are accurate statements, the correct answer is D. Summary: - Choice A is correct because the PNS is located outside the CNS. - Choice B is correct as the PNS includes nerves and ganglia. - Choice C is incorrect as it refers to the CNS (Brain & Spinal cord).

Correct Answer: A

Rationale: The correct answer is A: Hematoma. A hematoma is an abnormal collection of blood within tissues. This occurs due to broken blood vessels and can lead to swelling and localized pain. Thrombosis (B) is the formation of a blood clot within a blood vessel, not an accumulation of blood in tissue. An embolus (C) is a blood clot that travels through the bloodstream and gets lodged in a blood vessel. Hemorrhage (D) refers to the excessive bleeding from blood vessels. In this case, the most appropriate term for an abnormal accumulation of blood in a tissue is hematoma.

Correct Answer: A

Rationale: The correct answer is A: E. coli 0157:H7. This strain of E. coli has acquired virulence factors that allow it to cause severe illness in humans, such as bloody diarrhea and kidney failure. The transformation of E. coli from a commensal to a pathogenic strain is well-documented. In contrast, choices B and C involve species that are inherently pathogenic and not commensal. Choice D is too broad and includes a wide range of bacterial species that do not necessarily originate from the normal flora. Therefore, E. coli 0157:H7 is the best example of a commensal bacterium that has turned pathogenic due to the acquisition of virulence factors.

Correct Answer: C

Rationale: The correct answer is C because NADPH oxidase is not constitutively expressed as a complex of 5 subunits in unstimulated cells. Instead, it is assembled and activated upon stimulation, such as during the respiratory burst following phagocytosis. Choice A is correct as NADPH oxidase is indeed involved in the respiratory burst. Choice B is correct as mutations in NADPH oxidase subunits lead to impaired pathogen killing and recurrent infections. Choice D is correct as NADPH oxidase controls the production of reactive oxygen species.

Correct Answer: C

Rationale: The correct answer is C because B cell receptors, known as antibodies, are Y-shaped proteins with two identical antigen-binding sites. This feature allows B cells to bind to specific antigens with high specificity. Each B cell receptor can bind to a unique antigen, leading to the initiation of an immune response. Choice A is incorrect because B cell receptors can be secreted as antibodies to target antigens outside the cell. Choice B is incorrect because B cell receptors recognize antigens directly, not in combination with MHC molecules. Choice D is incorrect because B cells primarily recognize specific antigens rather than general PAMPs associated with pathogens.