Antigenic variation is used by bacteria to:

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 Gram stain differentiates bacteria based on cell wall structure. It classifies bacteria into Gram-positive (purple) and Gram-negative (pink) based on the presence of peptidoglycan in the cell wall. This method helps in identifying the bacterial species and determining appropriate treatment. Option A (Cell shape) is incorrect because the Gram stain focuses on cell wall composition, not cell shape. Option C (Flagella composition) is incorrect as the Gram stain does not assess flagella. Option D (Nutrient requirements) is incorrect as it does not relate to the purpose of the Gram stain.

Correct Answer: C

Rationale: The correct answer is C: Transcription. Transcription is the process of synthesizing RNA from a DNA template. During transcription, RNA polymerase binds to the DNA and produces a complementary RNA strand. This process is essential for gene expression. Explanation for why other choices are incorrect: A: Transposition involves the movement of genetic elements within a genome, not the production of RNA from DNA. B: Translation is the process of synthesizing proteins from mRNA, not the production of RNA from DNA. D: RNA splicing is the process of removing introns and joining exons in pre-mRNA to produce mature mRNA, not the initial production of RNA from DNA.

Correct Answer: B

Rationale: The correct answer is B. Bacilli are rod-shaped bacteria, some of which are endospore forming. Cocci are spherical, spirals are spiral-shaped, and vibrios are curved rod-shaped bacteria. Bacilli specifically refer to rod-shaped bacteria, making it the correct answer in this context.

Correct Answer: B

Rationale: The correct answer is B because viruses can indeed be cultured on hen embryos, cell cultures, and experimental animals in vitro. This method allows for the replication and study of viruses outside the host organism. Option A is incorrect as viral cultivation is possible in laboratory settings. Option C is incorrect because while viruses can be grown on nutrient media, it is not the only method. Option D is incorrect as viruses can be cultured in various types of cell cultures, not just human embryonic ones.