openstax microbiology test bank

Correct Answer: A

Rationale: The correct answer is A: Giardia lamblia. Giardia lamblia is a flagellated protozoan with two nuclei, known as the "falling leaf" appearance. It causes diarrhea in humans through ingestion of contaminated water or food. Entamoeba histolytica causes amoebic dysentery, characterized by bloody diarrhea and colitis. Trichomonas vaginalis is a sexually transmitted protozoan causing vaginal discharge but is not found in stool. Balantidium coli is a ciliated protozoan causing diarrhea but does not have flagellated forms.

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pyogenes. This is because Streptococcus pyogenes is a Gram-positive cocci in chains bacterium that is catalase-negative, making it the most likely causative agent in this scenario. Streptococcus pyogenes is a common pathogen causing bacterial endocarditis. Summary of other choices: B: Staphylococcus aureus is a Gram-positive cocci bacterium but is catalase-positive, so it is unlikely in this case. C: Enterococcus faecalis is a Gram-positive cocci bacterium, but it is catalase-negative, which is not consistent with the given information. D: Micrococcus luteus is a Gram-positive cocci bacterium but is catalase-positive, making it an unlikely causative agent.

Correct Answer: C

Rationale: The correct answer is C: Up to 3 months. Hepatitis B has an average incubation period of 60-90 days, which aligns with the timeframe of up to 3 months. This period refers to the time between exposure to the virus and the onset of symptoms. One week to 10 days (choice A) is too short for hepatitis B, as it typically takes longer to manifest. One month to 45 days (choice B) is also shorter than the average incubation period for hepatitis B. Up to 6 months (choice D) is too long for hepatitis B, as the virus typically shows symptoms within 3 months.

Correct Answer: D

Rationale: The correct answer is D because viruses have the ability to infect all organisms, including plants, bacteria, animals, and even fungi. Viruses are non-living entities that require a host cell to replicate and spread. They can infect a wide range of organisms by attaching to specific receptors on the host cell's surface. Therefore, the correct answer is D as viruses have the capability to infect all living organisms. Choices A, B, and C are incorrect because viruses can infect not only plants, bacteria, and animals but also other organisms, making choice D the most comprehensive and accurate option.

Correct Answer: B

Rationale: The correct answer is B: Protection against phagocytosis. The bacterial capsule is a protective layer outside the cell wall that helps bacteria evade phagocytosis by the host immune system. It acts as a physical barrier against immune cells like macrophages and neutrophils, allowing the bacteria to survive and multiply in the host. Energy production (A), DNA replication (C), and protein synthesis (D) are essential cellular functions but are not directly associated with the major function of the bacterial capsule, which is protection against phagocytosis.