Which of the following statements is FALSE regarding B cells?

Correct Answer: B

Rationale: B cells develop in the bone marrow, not the thymus. Firstly, hematopoietic stem cells in the bone marrow give rise to B cells. They undergo maturation and selection processes in the bone marrow, not in the thymus. Therefore, choice B is false. On the other hand, choices A, C, and D are correct. A is true because B cells with high affinity to self-antigens undergo apoptosis to prevent autoimmunity. C is true since B cells synthesize antibodies which can be displayed on their surface as B cell receptors. D is true because B cells can undergo class switching to produce different types of antibodies based on the immune response requirements.

Correct Answer: A

Rationale: The correct answer is A: IgG. IgG is the most abundant class of immunoglobulins in the body, constituting about 75% of total immunoglobulins. IgG plays a crucial role in long-term immunity, neutralizing toxins, and enhancing phagocytosis. IgE is involved in allergic reactions, IgD is mainly found on B cells and functions as a receptor, and IgM is the first antibody produced in response to an infection but is less abundant compared to IgG. Therefore, IgG is the correct choice based on its abundance and diverse functions in the immune system.

Correct Answer: A

Rationale: The correct answer is A: Erythrocytic schizogony. In this case, the patient most likely has malaria, specifically caused by Plasmodium falciparum. The fever attacks every 2 days (tertian fever) are characteristic of P. falciparum infection. The cycle of erythrocytic schizogony in P. falciparum is around 48 hours, leading to the recurring fever pattern. Choices B, C, and D are incorrect as tissue schizogony does not cause the characteristic fever pattern, exotoxins are not typically involved in malaria fever, and gametocytes do not directly cause fever attacks.

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pyogenes. 1. Gram-positive cocci in chains suggest streptococci. 2. Catalase-negative indicates it's not staphylococci. 3. Beta-hemolytic points towards Group A Streptococcus (S. pyogenes). Summary: B. Streptococcus pneumoniae is not beta-hemolytic. C. Enterococcus faecalis is not typically chains. D. Staphylococcus aureus is catalase-positive.

Correct Answer: C

Rationale: The correct answer is C: cytomegalovirus (CMV). Congenital CMV infections are caused by the transmission of CMV from a pregnant woman to her fetus. CMV is a type of herpes virus, not a coronavirus (A), herpes simplex virus (B), or Epstein-Barr virus (D). CMV is known to cause serious health issues in newborns, making it crucial to identify and manage during pregnancy.

Correct Answer: D

Rationale: The correct answer is D: rectum. Pinworms typically inhabit the rectum area in humans, where they lay their eggs. This is because the female pinworm migrates to the rectum at night to deposit her eggs near the anus. Other choices are incorrect because pinworms do not reside in the duodenum (A), ileum (B), or transverse colon (C) as their primary location is in the lower gastrointestinal tract near the anus.

Correct Answer: B

Rationale: The correct answer is B: Herpangina. Family Parvoviridae includes Parvovirus B19, which causes Fifth disease, aplastic crisis in chronic anemia, and fetal infections. Herpangina is caused by Enteroviruses, not Parvoviridae. Parvovirus B19 specifically targets erythroid progenitor cells, leading to anemia in susceptible individuals. Fetal infections can result in hydrops fetalis. Aplastic crisis occurs in patients with chronic anemia due to suppression of erythropoiesis by the virus.

Correct Answer: A

Rationale: The correct answer is A: Clostridium botulinum. This bacterium is associated with food poisoning from improperly canned foods due to its ability to produce botulinum toxin, a potent neurotoxin that causes botulism. Improper canning allows spores of Clostridium botulinum to survive and germinate, producing the toxin in anaerobic conditions. The other choices are incorrect because Escherichia coli, Salmonella enterica, and Vibrio cholerae are not typically associated with food poisoning from improperly canned foods. Escherichia coli and Salmonella are more commonly linked to contaminated water or undercooked food, while Vibrio cholerae causes cholera primarily through contaminated water sources.

Correct Answer: B

Rationale: The correct answer is B: Flagella. Flagella are whip-like appendages used by bacteria for movement. They rotate in a corkscrew motion to propel the bacteria through their environment. Pili (choice A) are hair-like structures used for attachment, not movement. Capsules (choice C) are protective layers around bacteria, not involved in movement. Fimbriae (choice D) are also used for attachment and biofilm formation, not for movement. Therefore, the correct choice is B as flagella are specifically adapted for bacterial motility.