microbiology test bank

Correct Answer: B

Rationale: The correct answer is B: kidneys. The kidneys are the primary organs responsible for excreting drugs from the body through urine. They filter the blood and remove waste products, including drugs, through the process of urine formation. The lungs primarily excrete gases and volatile substances, not drugs. The small intestines are mainly involved in absorption of nutrients, not drug excretion. The spleen is part of the immune system and does not play a direct role in drug excretion.

Correct Answer: D

Rationale: The correct answer is D because all three bacteria listed produce toxins that cause damage to host tissues. Clostridium tetani produces tetanospasmin toxin causing tetanus, Vibrio cholerae produces cholera toxin leading to severe diarrhea, and Staphylococcus aureus releases toxins causing tissue damage in various infections. Therefore, all of the above choices are correct in terms of producing toxins that harm host tissues.

Correct Answer: A

Rationale: The correct answer is A because penicillins and cephalosporins inactivate transpeptidase activity of penicillin binding proteins, leading to disruption of bacterial cell wall synthesis. This mechanism makes them bactericidal, not bacteriostatic (choice B). Choice C is incorrect as penicillins and cephalosporins target cell wall synthesis, not the cytoplasmic membrane. Choice D is incorrect as option A is the correct statement.

Correct Answer: B

Rationale: The correct answer is B because the structure of the cytoplasmic membrane in gram-positive and gram-negative bacteria is fundamentally different. Gram-positive bacteria have a single-layered cytoplasmic membrane, while gram-negative bacteria have a double-layered cytoplasmic membrane with an additional outer membrane. This key difference is crucial for various functions such as antibiotic resistance and nutrient transport. Rationale for the incorrect choices: A: Gram-positive bacteria have a single-layered cytoplasmic membrane, not a double-layered one. C: Prokaryotes do have a cytoplasmic membrane, which is essential for maintaining cell integrity and regulating the passage of molecules. D: Gram-negative bacteria have a double-layered cytoplasmic membrane, not a three-layered one.

Correct Answer: D

Rationale: The correct answer is D, Salmonella typhi, because it is a motile bacterium due to possessing flagella that aid in movement. Bacillus anthracis (A) is non-motile, Klebsiella pneumoniae (B) lacks flagella for motility, and Shigella flexneri (C) is non-motile as well. Salmonella typhi (D) is known for its flagella-driven motility, allowing it to move and spread within its host and environment. Flagella are essential for bacterial motility, enabling them to navigate and colonize different environments efficiently.