Correct Answer: B

Rationale: The correct answer is B because anaerobic bacteria can grow in environments without oxygen. Anaerobic bacteria do not require oxygen for their metabolism and energy production. They can thrive in oxygen-deprived conditions by using alternative electron acceptors. Choice A is incorrect because anaerobic bacteria do not require oxygen to survive. Choice C is incorrect because anaerobic bacteria typically cannot survive in the presence of high concentrations of oxygen. Choice D is incorrect because anaerobic bacteria do not perform photosynthesis.

Correct Answer: B

Rationale: The correct answer is B: Within 24 hours. Rabies post-exposure prophylaxis should ideally be initiated as soon as possible after a potentially infectious bite to prevent the virus from spreading and causing symptoms. Immediate treatment is crucial to prevent the virus from reaching the central nervous system. Waiting beyond 24 hours increases the risk of the virus reaching the brain and becoming fatal. Choices A, C, and D are incorrect because waiting for 6 months, a week, or 2 weeks respectively would significantly delay treatment, allowing the virus to progress and potentially become untreatable.

Correct Answer: C

Rationale: The correct answer is C: rotaviruses. Rotaviruses are the most common cause of infectious diarrhea in infants and children due to their highly contagious nature and ability to spread easily in childcare settings. They are known to cause severe diarrhea, vomiting, and dehydration in young children. Noroviruses (A), adenoviruses (B), and caliciviruses (D) can also cause diarrhea, but rotaviruses are specifically known for their prevalence and severity in the pediatric population. This is why C is the correct answer.

Correct Answer: A

Rationale: The correct answer is A: Protozoa. Protozoa are single-celled eukaryotic organisms, meaning they have a nucleus and other membrane-bound organelles. Eukaryotes have complex cellular structures that include a nucleus, mitochondria, and other organelles. Therefore, protozoa are eukaryotes. Viruses (B) are not considered cells and lack cellular structures. Viroids (C) are smaller infectious agents that consist of only RNA, lacking the cellular structure of eukaryotes. Prions (D) are infectious proteins and do not possess cellular structures like eukaryotes. So, protozoa are the only choice that relates to eukaryotes due to their cellular structure.

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.