microbiology test bank

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.

Correct Answer: B

Rationale: The correct answer is B: Phylum. After class in the classification system comes phylum. The classification system starts with the broadest category, which is the kingdom, followed by phylum, class, order, family, genus, and species. Phylum is a higher level of classification than class, so it comes next in the hierarchy. Domain is a higher level than kingdom, and order is a lower level of classification than class. Therefore, the correct sequence is kingdom, phylum, class, order.

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: D

Rationale: The correct answer is D because enveloped viruses have a lipid bilayer envelope derived from the host cell membrane, which is a complex structure, not exhibiting any specific symmetry. Choice A (cubic symmetry) is incorrect as enveloped viruses do not have any specific geometric shape. Choice B (spiral symmetry) is incorrect as this type of symmetry is typically seen in non-enveloped viruses like helical viruses. Choice C (complex symmetry) is also incorrect as enveloped viruses do not exhibit a specific symmetrical pattern. Therefore, the correct answer is D because enveloped viruses do not have a defined symmetry and can vary in shape and structure.

Correct Answer: C

Rationale: Rationale: 1. Both Clostridium botulinum and Bacillus anthracis are known to form spores. 2. Spore formation is a mechanism for survival in harsh conditions. 3. Both bacteria are capable of causing severe diseases in humans. Summary: - Choice A and B are incorrect because each bacteria listed is capable of spore formation. - Choice D is incorrect as both bacteria mentioned can form spores to survive extreme conditions.