Which explanation best accounts for the differences in bacterial movement between pattern A (smooth swimming) and pattern B (tumbling)?

• A. Pattern A occurs when the cell is in a nutrient-poor environment, and pattern B occurs in a nutrient-rich environment.
• B. Pattern A results from counterclockwise rotation of flagella causing the cell to move forward, while pattern B results from clockwise rotation causing the cell to tumble.
• C. Pattern A is caused by pili-mediated gliding, while pattern B is due to flagellar rotation.
• D. Pattern A is due to the absence of flagella, while pattern B occurs when flagella are present.

Answer: (B)

Verified step by step guidance

1. Understand that bacterial movement is primarily driven by the rotation of flagella, which are whip-like structures that propel the cell through liquid environments.
2. Recognize that the direction of flagellar rotation affects the movement pattern: counterclockwise rotation typically causes flagella to bundle together, resulting in smooth, forward swimming (pattern A).
3. Know that clockwise rotation of flagella causes the bundle to fall apart, leading to tumbling behavior (pattern B), which reorients the bacterium randomly.
4. Relate these movement patterns to environmental conditions: smooth swimming allows bacteria to move toward favorable environments, while tumbling helps them change direction when conditions are less favorable.
5. Eliminate incorrect explanations by noting that pili-mediated gliding and absence of flagella do not account for the described swimming and tumbling behaviors, which are specifically linked to flagellar rotation direction.