Questions: Which is a characteristic of bacterial spores? - Comma-shaped motile bacteria - Usually pathogenic cocci that cause pustules - Created as part of the bacterial reproductive cycle - Difficult to destroy because they have resistant external structures

The answer is the fourth one: Difficult to destroy because they have resistant external structures.

Explanation for each option:

1. Comma-shaped motile bacteria: This describes the shape and motility of certain bacteria, such as Vibrio species, but it is not a characteristic of bacterial spores. Bacterial spores are not defined by shape or motility.

2. Usually pathogenic cocci that cause pustules: This describes a type of bacteria (cocci) that can cause infections, but it does not relate to bacterial spores. Spores are a form of survival, not a specific type of pathogenic bacteria.

3. Created as part of the bacterial reproductive cycle: This is incorrect because bacterial spores are not part of the reproductive cycle. They are formed as a survival mechanism under unfavorable conditions, not for reproduction.

4. Difficult to destroy because they have resistant external structures: This is correct. Bacterial spores are known for their resistance to extreme conditions, including heat, desiccation, and chemicals, due to their tough external structures.

In summary, bacterial spores are characterized by their resistance to destruction, making the fourth option the correct answer.