The site where B cells mature is

Correct Answer: C

Rationale: The correct answer is C: Bone marrow. B cells undergo maturation in the bone marrow, where they develop from hematopoietic stem cells. This is where they acquire their antigen receptors and differentiate into mature B cells. Lymph nodes (A) are primarily responsible for filtering lymph and containing immune cells. The spleen (B) is involved in filtering blood and storing immune cells. The thymus (D) is where T cells mature, not B cells. Therefore, the correct site for B cell maturation is the bone marrow.

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: C

Rationale: The primary function of white blood cells is to protect the body from foreign substances such as bacteria, viruses, and other pathogens. They do this by identifying and attacking these invaders to prevent infections and maintain overall health. White blood cells are a crucial part of the immune system and play a key role in defending the body against diseases. Clotting and sealing damaged blood vessels (choice A) is primarily done by platelets, not white blood cells. Transporting oxygen and carbon dioxide (choice B) is the function of red blood cells, not white blood cells. Producing hormones (choice D) is mainly performed by endocrine glands, not white blood cells.

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.