Human pathogens are considered which of the following members of the bacterial world?

• A. Saprophytic bacteria
• B. Nitrogen-fixing bacteria
• C. Photosynthetic bacteria
• D. Parasitic bacteria

Answer: (D)

Verified step by step guidance

1. Understand the definitions of the bacterial categories given: Saprophytic bacteria obtain nutrients from dead or decaying organic matter; Nitrogen-fixing bacteria convert atmospheric nitrogen into forms usable by plants; Photosynthetic bacteria produce energy through photosynthesis.
2. Recognize that human pathogens are bacteria that cause disease by living on or inside a host organism, often deriving nutrients at the host's expense.
3. Identify that bacteria which live in or on a host and cause harm are classified as parasitic bacteria.
4. Compare the characteristics of parasitic bacteria with the other categories to confirm that human pathogens fit the parasitic lifestyle rather than saprophytic, nitrogen-fixing, or photosynthetic.
5. Conclude that human pathogens are considered parasitic bacteria because they depend on a host for survival and often cause disease.