Attractants and repellents are detected by chemoreceptors that can trigger a. different flagella to rotate to change direction toward or away from the source of the attractants or repellents. b. the rotary flagella to change their rotation to allow the bacterium to change direction randomly. c. the flagella to whip in unison. d. different flagella to stop or start to allow cell movement.

b. the rotary flagella to change their rotation to allow the bacterium to change direction randomly

Explanation:

The bacterial flagella are made up of flagellin protein. The bacterial flagella is divided into three parts hook, filaments, and the basal body. Rotor is present in bacterial flagella which extends to the cytoplasm and makes C ring.  

C ring contains several switch proteins that change the rotation of the flagella instantly in response to repellent or attractant which allows to change the direction of bacteria randomly. Bacterial Flagella can move clockwise and counterclockwise. Therefore the right answer is B.

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