Which of the following is a role of helpful bacteria in humans?

• A. Producing botulinum toxin that leads to flaccid paralysis
• B. Performing photosynthesis to generate oxygen in human tissues
• C. Causing influenza by infecting respiratory epithelial cells
• D. Producing vitamin K in the intestine

Answer: (D)

Verified step by step guidance

1. Identify the role of helpful bacteria in humans by focusing on their beneficial functions rather than harmful effects or unrelated processes.
2. Recognize that producing botulinum toxin is a harmful activity caused by certain bacteria, not a helpful role.
3. Understand that performing photosynthesis is a process carried out by plants and some bacteria, but not by bacteria living in human tissues.
4. Note that causing influenza is a viral infection, not a bacterial function, and thus not a helpful role of bacteria.
5. Recall that helpful bacteria in the human intestine synthesize essential nutrients, such as vitamin K, which is important for blood clotting and overall health.