Etiological factors for the infectious diseases are often microorganisms with various ultrastructure. Which of the following microorganism groups relates to the eukaryotes?

Correct Answer: A

Rationale: The correct answer is A: Protozoa. Protozoa are eukaryotic microorganisms, meaning they have a true nucleus and membrane-bound organelles. This relates to the question as eukaryotes are organisms with complex cells containing these features. Viruses (B) are non-living entities that require a host cell to replicate, lacking cellular structures. Viroids (C) are smaller than viruses and consist of only RNA, lacking a protein coat. Prions (D) are misfolded proteins causing diseases but are not considered microorganisms nor do they have cellular structure. Thus, protozoa are the only eukaryotic microorganism group among the options.

Correct Answer: A

Rationale: The correct answer is A: evade host immune responses. Antigenic variation allows bacteria to change their surface antigens, making it difficult for the host immune system to recognize and attack them effectively. This enhances the bacteria's ability to evade immune responses and establish infection. B: Increase antibiotic susceptibility is incorrect because antigenic variation does not directly impact the susceptibility of bacteria to antibiotics. C: Increase peptidoglycan synthesis is incorrect because antigenic variation is not related to the synthesis of peptidoglycan, which is a major component of the bacterial cell wall. D: Enhance motility is incorrect because antigenic variation does not directly affect the motility of bacteria. In summary, antigenic variation in bacteria primarily serves to help them evade host immune responses, making option A the correct answer.

Correct Answer: B

Rationale: The correct answer is B: resisting phagocytosis. Bacterial capsules are composed of polysaccharides that help bacteria evade phagocytosis by immune cells. This physical barrier prevents immune cells from engulfing and destroying the bacteria. Facilitating motility (A), synthesizing DNA (C), and producing energy (D) are not primary functions of bacterial capsules. Motility is usually facilitated by flagella, DNA synthesis occurs in the bacterial chromosome, and energy production is typically carried out by metabolic processes within the bacterial cell.

Correct Answer: B

Rationale: The correct answer is B: protein synthesis. Bacterial ribosomes are responsible for translating messenger RNA into proteins through a process called translation. Ribosomes are composed of both protein and RNA molecules and facilitate the binding of transfer RNA to the messenger RNA to assemble the amino acids in the correct order to form a protein. DNA replication (A) is carried out by enzymes such as DNA polymerase, not ribosomes. Cell wall synthesis (C) is a process involving enzymes that build the structure of the cell wall in bacteria. RNA splicing (D) is a eukaryotic process that involves removing introns from pre-mRNA molecules, which is not a function of bacterial ribosomes.

Correct Answer: A

Rationale: The presence of rods with polar dark blue granules stained by Neisser's method indicates metachromatic granules consistent with Corynebacterium diphtheriae. The characteristic staining pattern is due to the presence of polar granules in the bacterial cells, a feature specific to Corynebacterium diphtheriae. Bacillus anthracis, Clostridium tetani, and Escherichia coli do not exhibit this staining pattern or morphology typical of Corynebacterium diphtheriae, making them incorrect choices.