microbiology test bank

Correct Answer: B

Rationale: The correct answer is B: genotype. The genotype refers to the actual genetic makeup of an organism, including all the genes and alleles present in its DNA. This determines the traits and characteristics of an organism. Phenotype (A) is the observable physical or biochemical characteristics of an organism. Conjugation (C) is a process in bacteria involving the transfer of genetic material. Construct (D) is not a term related to genetics. Therefore, the correct choice is B as it specifically refers to the genetic composition of an organism.

Correct Answer: A

Rationale: The correct answer is A: Nitrogen-fixing bacteria. These bacteria can convert atmospheric nitrogen into a form that plants can use, promoting plant growth. Denitrifying bacteria (B) convert nitrates back into atmospheric nitrogen. Photosynthetic bacteria (C) use photosynthesis to produce energy and don't fix nitrogen. Fermentative bacteria (D) break down organic compounds without fixing nitrogen. In summary, only nitrogen-fixing bacteria (A) play a crucial role in the nitrogen cycle by converting atmospheric nitrogen into a usable form for plants.

Correct Answer: A

Rationale: The correct answer is A, Clostridium botulinum. This bacterium produces botulinum toxin, leading to botulism. It is commonly found in soil and improperly canned food. Clostridium tetani causes tetanus, Staphylococcus aureus causes food poisoning, and Salmonella enterica causes salmonellosis. Therefore, A is correct due to its association with botulism, while the other choices are incorrect for causing different diseases.

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: C

Rationale: The correct answer is C because hemagglutinin of influenza viruses serves as an attachment molecule to the receptor of the target cell, facilitating viral entry. This is crucial for the virus to infect host cells. Choice A is incorrect because hemagglutinin is not part of the viral capsid but rather a surface protein. Choice B is incorrect as hemagglutinin is not directly involved in viral replication, but in host cell attachment. Choice D is incorrect as hemagglutinin is highly antigenic, triggering the host's immune response.