Correct Answer: A

Rationale: The correct answer is A: Absence of a cell wall. L-form transformation is a phenomenon where the pathogen loses its cell wall, making it resistant to antibiotics like penicillin. The absence of a cell wall allows the pathogen to survive in a hostile environment. Choice B: Absence of flagella is incorrect because flagella are responsible for motility and not directly related to L-form transformation. Choice C: Absence of a capsule is incorrect as the capsule is a protective layer outside the cell wall and not affected by L-form transformation. Choice D: Absence of a spore is incorrect because spores are a dormant form of bacteria and not related to L-form transformation.

Correct Answer: C

Rationale: The correct answer is C because Koch's postulate states that a microorganism must be isolated in pure culture, grown in a laboratory setting, and then inoculated into animals to reproduce the same disease seen in the original host. This step demonstrates a direct cause-and-effect relationship between the isolated microorganism and the disease. Choice A is incorrect because not all cases of a disease may have the same microorganism present. Choice B is incorrect as isolating the microorganism alone does not prove its pathogenicity. Choice D is incorrect as it does not address the need for experimental reproduction of the disease in a new host.

Correct Answer: A

Rationale: The correct sequence of stages in the multiplication of animal viruses is as follows: 1. Adsorption: Virus attaches to host cell. 2. Penetration: Virus enters host cell. 3. Uncoating: Viral genetic material is released. 4. Replication: Viral genetic material replicates. 5. Assembly: New viral particles are assembled. 6. Release: New viral particles are released from the host cell. Choice A is correct as it follows the correct chronological order of virus multiplication stages. Choice B is incorrect as it has the wrong order of penetration and adsorption. Choice C is incorrect as it has the wrong order of adsorption, uncoating, and penetration. Choice D is incorrect as it has the wrong order of penetration and uncoating.

Correct Answer: D

Rationale: The correct answer is D: Thin mobile bacillus with central spore. This is because the causative agent of botulism, Clostridium botulinum, is a gram-positive bacillus that typically appears as a thin rod-shaped bacterium with a central endospore. This characteristic morphology is essential in the identification of Clostridium botulinum. A: Gram-positive bacillus with subterminal spore - This is incorrect as Clostridium botulinum typically has a central endospore, not a subterminal one. B: Thick gram-positive non-spore-forming bacillus - This is incorrect as Clostridium botulinum forms endospores, although they are not thick. C: Gram-positive bacillus with terminal spore - This is incorrect as the spore of Clostridium botulinum is typically central, not terminal.

Correct Answer: A

Rationale: The correct answer is A: Vibrio cholerae. 1. Vibrio cholerae is a Gram-negative, comma-shaped bacterium known to cause cholera. 2. Shigella dysenteriae causes dysentery, not cholera. 3. Salmonella typhi causes typhoid fever, not cholera. 4. Campylobacter jejuni causes gastroenteritis, not cholera. Therefore, based on the symptoms presented and the characteristics of the bacterium, Vibrio cholerae is the most likely microorganism.