Final answer:
Bacterial flagella rotate in a clockwise direction to cause a tumbling motion, which interrupts forward movement and causes the cell to reorient rather than move efficiently. This is contrasted with a counterclockwise rotation during running, which bundles the flagella for streamlined movement.
Step-by-step explanation:
The movement of flagella in bacteria is vital to their mobility. When bacteria move using tumbling motion, they are propelled by flagella that rotate in a clockwise direction. This rotation causes the previously bundled flagella to splay out, which interrupts their streamlined movement and results in a tumbling motion, reorienting the bacterium but not leading to meaningful forward movement. Conversely, when flagella rotate in a counterclockwise direction during running, they bundle together and push the cell forward in a more streamlined and efficient manner. This behavior is part of a strategy called chemotaxis, where bacteria adjust their movements in response to chemical gradients, seeking out attractants and avoiding repellents.