Peritrichous bacteria make a 'run' when:

• A. all their flagella rotate clockwise and spread apart
• B. they are exposed to antibiotics
• C. they lose their flagella
• D. all their flagella rotate counterclockwise and bundle together

Answer: (D)

Verified step by step guidance

1. Understand the terms: 'peritrichous bacteria' have flagella distributed all around their surface, which they use for movement.
2. Recall that bacterial movement involves two main behaviors: 'runs' and 'tumbles'. A 'run' is a smooth, straight movement, while a 'tumble' is a random change in direction.
3. Know that the direction of flagellar rotation determines the movement type. For peritrichous bacteria, when all flagella rotate counterclockwise (CCW), they bundle together, propelling the bacterium forward in a 'run'.
4. Conversely, when the flagella rotate clockwise (CW), they spread apart, causing the bacterium to 'tumble' and change direction.
5. Therefore, the correct condition for a 'run' is when all flagella rotate counterclockwise and bundle together, enabling smooth forward movement.