Which type of bacteria is capable of fixing nitrogen?

Correct Answer: A

Rationale: The correct answer is A: Nitrogen-fixing bacteria. These bacteria can convert atmospheric nitrogen into a form that plants can use, promoting plant growth. Denitrifying bacteria (B) convert nitrates back into atmospheric nitrogen. Photosynthetic bacteria (C) use photosynthesis to produce energy and don't fix nitrogen. Fermentative bacteria (D) break down organic compounds without fixing nitrogen. In summary, only nitrogen-fixing bacteria (A) play a crucial role in the nitrogen cycle by converting atmospheric nitrogen into a usable form for plants.

Correct Answer: B

Rationale: The correct answer is B: Escherichia coli. E. coli is a common bacterium found in the gastrointestinal tract and is a leading cause of UTIs. It has specific virulence factors that enable it to adhere to and infect the urinary tract. Salmonella enterica causes food poisoning, Vibrio cholerae causes cholera, and Streptococcus pyogenes causes strep throat and skin infections, not UTIs. Therefore, B is the correct answer as it is the only bacterium known for causing UTIs.

Correct Answer: B

Rationale: The correct answer is B because anaerobic bacteria can grow in environments without oxygen. Anaerobic bacteria do not require oxygen for their metabolism and energy production. They can thrive in oxygen-deprived conditions by using alternative electron acceptors. Choice A is incorrect because anaerobic bacteria do not require oxygen to survive. Choice C is incorrect because anaerobic bacteria typically cannot survive in the presence of high concentrations of oxygen. Choice D is incorrect because anaerobic bacteria do not perform photosynthesis.

Correct Answer: B

Rationale: Step 1: Gram-negative, comma-shaped bacterium suggests a curved rod morphology, typical of Campylobacter jejuni. Step 2: Motility is a characteristic of Campylobacter species. Step 3: Campylobacter jejuni is a common cause of bacterial diarrhea in humans. Step 4: Vibrio cholerae causes cholera, not typically associated with comma-shaped morphology. Shigella dysenteriae and Escherichia coli are not comma-shaped.

Correct Answer: B

Rationale: The main function of bacterial pili is to facilitate conjugation and adhesion. Pili are hair-like appendages on bacteria that help in cell-to-cell interactions. They play a crucial role in bacterial conjugation by allowing the transfer of genetic material between cells. Additionally, pili help bacteria adhere to surfaces or host cells, aiding in colonization and biofilm formation. Choices A and D are incorrect because protein synthesis and toxin secretion are not the primary functions of pili. Choice C is incorrect as bacterial motility is mainly mediated by flagella, not pili.