The cytoplasmic membrane of the eukaryotes, in contrast to the one of prokaryotes, has:

Correct Answer: D

Rationale: The correct answer is D: sterols. Eukaryotic cytoplasmic membranes contain sterols, such as cholesterol, which provide stability and regulate fluidity. This is a key characteristic that distinguishes them from prokaryotic membranes. Cellulose (A) is a component of plant cell walls, not the cytoplasmic membrane. Starch (B) is a carbohydrate used for energy storage in plants. Chitin (C) is a component of fungal cell walls and arthropod exoskeletons, not found in eukaryotic cytoplasmic membranes.

Correct Answer: D

Rationale: The correct answer is D: Salmonella typhi. Typhoid fever is caused by the bacterium Salmonella typhi. This bacterium is responsible for causing the systemic infection that leads to symptoms such as high fever, abdominal pain, and diarrhea. Yersinia pestis (choice A) causes plague, Shigella dysenteriae (choice B) causes dysentery, and Escherichia coli (choice C) can cause various gastrointestinal infections, but not typhoid fever. Salmonella typhi specifically targets the intestines and is transmitted through contaminated food or water. Therefore, choice D is the correct answer for the cause of typhoid fever.

Correct Answer: D

Rationale: The correct answer is D: Rubella virus. Rubella virus does not belong to the family Paramyxoviridae because it belongs to the Togaviridae family. The other choices, A (Measles virus), B (Respiratory syncytial virus), and C (Mumps virus) are all members of the Paramyxoviridae family. This classification is based on the genetic and structural characteristics of the viruses. Rubella virus is distinct in its genetic composition and replication cycle compared to the Paramyxoviridae family, making it the correct choice.

Correct Answer: C

Rationale: Legionella pneumophila is a Gram-negative coccobacillus. It is not a coccus (round shape), spiral bacterium, or Gram-positive coccobacillus. The correct answer is C because Legionella pneumophila has a characteristic coccobacillary shape and stains Gram-negative due to its cell wall composition. The other choices are incorrect because they do not accurately describe the morphology or staining characteristics of Legionella pneumophila.

Correct Answer: D

Rationale: Rationale: 1. Rickettsiae are obligate intracellular bacteria, hence they do not form spores, capsules, or flagella. 2. They have a slim glycocalyx layer, aiding in attachment to host cells. 3. Bipolar fimbriae are structures that help in adhesion to host cells. Therefore, all statements (A, B, and C) are true for Rickettsiae, making option D the correct answer. Other choices are incorrect as they do not accurately describe the characteristics of Rickettsiae.