The white pulp and red pulp are part of which immune organ:

Correct Answer: C

Rationale: The correct answer is C: Spleen. The white pulp of the spleen contains lymphocytes that help in immune responses. The red pulp filters blood and removes old or damaged red blood cells. The thymus (A) is responsible for T cell maturation, lymph nodes (B) filter lymph, and lymphoid tissue (D) includes various lymphoid organs but does not specifically refer to the spleen's distinct white and red pulp structure. Thus, the spleen is the only organ among the choices that has both white and red pulp components essential for immune functions.

Correct Answer: A

Rationale: The correct answer is A: Vibrio cholerae. This bacterium produces the cholera toxin, an enterotoxin that causes profuse watery diarrhea by disrupting the normal function of the intestines. Vibrio cholerae is specifically known for causing cholera, a severe diarrheal disease. Clostridium botulinum (B) produces botulinum toxin, causing botulism (paralysis, not diarrhea). Escherichia coli (C) can produce enterotoxins, but the question specifies a specific enterotoxin causing diarrhea, which is not a characteristic of all strains of E. coli. Streptococcus pneumoniae (D) is a common cause of respiratory infections but does not produce an enterotoxin causing diarrhea.

Correct Answer: B

Rationale: Step-by-step rationale for choice B being correct: 1. The conclusion should be based on evidence or observations. 2. "Doubtful" suggests uncertainty, indicating lack of definitive safety. 3. Choice A is too absolute without considering potential risks. 4. Choice C uses extreme language without proper evidence. 5. Choice D is overly definitive without considering varying levels of contamination. Therefore, choice B is the most reasonable conclusion.

Correct Answer: A

Rationale: The correct answer is A: Mycobacterium tuberculosis. This bacterium is responsible for causing tuberculosis. It is a slow-growing, acid-fast bacillus that primarily affects the lungs. Mycobacterium tuberculosis is transmitted through the air via respiratory droplets. Choice B, Streptococcus pneumoniae, is a common cause of pneumonia but not tuberculosis. Choice C, Salmonella enterica, causes food poisoning. Choice D, Neisseria meningitidis, causes meningitis, not tuberculosis. Therefore, Mycobacterium tuberculosis is the correct answer based on its characteristics and mode of transmission.

Correct Answer: B

Rationale: The correct answer is B: Trimethoprim. Trimethoprim is a folate antagonist that inhibits dihydrofolate reductase, an enzyme essential for folate metabolism in bacteria. This disrupts bacterial DNA synthesis, leading to bacteriostatic effects. Methyl Penicillin (A) is a beta-lactam antibiotic that interferes with bacterial cell wall synthesis. Vancomycin (C) inhibits cell wall synthesis by binding to D-Ala-D-Ala terminus of cell wall precursors. Gentamicin (D) inhibits bacterial protein synthesis by binding to the 30S subunit of the bacterial ribosome.

Correct Answer: C

Rationale: The correct answer is C: Kirby-Bauer disk diffusion test. This test is used to determine the antibiotic susceptibility of bacteria by measuring the zone of inhibition around antibiotic-soaked paper disks. It helps identify which antibiotics are effective against the bacteria being tested. This test is crucial in guiding antibiotic treatment decisions. A: Gram stain is used to classify bacteria based on their cell wall composition and morphology, not for antibiotic susceptibility testing. B: Catalase test is used to differentiate between catalase-positive and catalase-negative bacteria, not for antibiotic susceptibility testing. D: Endospore stain is used to detect the presence of endospores in bacteria, not for antibiotic susceptibility testing.

Correct Answer: B

Rationale: The correct answer is B: protein synthesis. Bacterial ribosomes are responsible for translating messenger RNA into proteins through a process called translation. Ribosomes are composed of both protein and RNA molecules and facilitate the binding of transfer RNA to the messenger RNA to assemble the amino acids in the correct order to form a protein. DNA replication (A) is carried out by enzymes such as DNA polymerase, not ribosomes. Cell wall synthesis (C) is a process involving enzymes that build the structure of the cell wall in bacteria. RNA splicing (D) is a eukaryotic process that involves removing introns from pre-mRNA molecules, which is not a function of bacterial ribosomes.

Correct Answer: B

Rationale: The correct answer is B: Corynebacterium diphtheriae. This bacterium produces a toxin that causes diphtheria by inhibiting protein synthesis, leading to the formation of a pseudomembrane in the throat. Bordetella pertussis causes whooping cough, Streptococcus pyogenes causes strep throat, and Neisseria meningitidis causes meningitis. Corynebacterium diphtheriae is the only bacterium among the choices known to cause diphtheria due to its specific toxin production.

Correct Answer: A

Rationale: Rifampicin is the correct answer because it inhibits RNA transcription in mycobacteria by binding to the bacterial RNA polymerase. This prevents the synthesis of RNA, leading to the inhibition of protein production essential for bacterial growth. Isoniazid inhibits mycolic acid synthesis, Streptomycin inhibits protein synthesis, and Ethionamide disrupts mycolic acid synthesis. These mechanisms are different from inhibiting RNA transcription, making them incorrect choices.