Correct Answer: C

Rationale: The correct answer is C: Thick peptidoglycan layer. Gram-positive bacteria have a thick peptidoglycan layer in their cell wall, which retains the crystal violet stain in the Gram staining process, leading to a purple color. This thick layer is a defining characteristic of Gram-positive bacteria. Rationale: A: Thin peptidoglycan layer is incorrect because Gram-positive bacteria have a thick peptidoglycan layer. B: Presence of an outer membrane is incorrect because Gram-positive bacteria lack an outer membrane. D: Presence of lipopolysaccharides is incorrect because lipopolysaccharides are typically found in the outer membrane of Gram-negative bacteria, not Gram-positive bacteria.

Correct Answer: A

Rationale: The correct answer is A: Trichomonads. Trichomonads are pear-shaped protozoa, typically 6-13 micrometers long, with one nucleus, undulating membrane, and four flagella at the front. These characteristics match the description provided in the question. Trichomonads are commonly found in oral cavities and can cause gum infections like periodontosis. Summary: - B: Leishmania - Leishmania is a flagellated protozoan responsible for Leishmaniasis, not typically found in the oral cavity. - C: Amoebae - Amoebae are not pear-shaped and do not have the specific characteristics described in the question. - D: Balantidia - Balantidia are ciliated protozoa, not flagellated like trichomonads, and are not typically associated with gum infections.

Correct Answer: A

Rationale: The correct answer is A: Clostridium tetani. The presence of Gram-positive rods with terminal spores resembling drumsticks indicates Clostridium tetani, the causative agent of tetanus. This bacterium forms spores at one end, giving it a drumstick appearance under the microscope. Clostridium perfringens (B) and Clostridium botulinum (D) do not have terminal spores. Bacillus anthracis (C) forms spores but typically appears as a square-ended or bamboo stick shape. Therefore, based on the microscopy findings, Clostridium tetani is the most likely microorganism responsible for the wound infection.

Correct Answer: C

Rationale: The correct answer is C (60 years) because as individuals age, their immune system weakens, making them more susceptible to infectious diseases. Around the age of 60, people are more likely to succumb to infections, leading to a higher mortality rate. Choices A, B, and D are incorrect because they are younger ages, and the likelihood of infectious diseases causing a significant proportion of deaths increases with age.

Correct Answer: D

Rationale: The correct answer is D: Paramyxoviridae. Mumps virus is a member of the Paramyxoviridae family, based on its characteristics such as structure, genome organization, and replication cycle. Paramyxoviruses are enveloped, non-segmented RNA viruses with a helical nucleocapsid. They replicate in the cytoplasm and bud from the host cell membrane. Coronaviridae (A) are a different family of viruses with distinct characteristics. Picornaviridae (B) and Orthomyxoviridae (C) are also different families with unique features that do not match those of the mumps virus.