Concept: This question tests your understanding of various physiological processes in the human body, including nerve impulse conduction, sensory perception (hearing and vision), and reflexes.

Why (C) is incorrect: Rods are indeed very sensitive to light, but they are responsible for scotopic vision (dim light or night vision), not daylight vision. They detect shades of gray and are not involved in color perception. Cones are responsible for daylight (photopic) vision and color perception.

Why other options are correct:

• (A) An action potential moves unidirectionally because the segment of the axon that has just fired is in a refractory period, preventing backward propagation.
• (B) When hair cells in the cochlea are stimulated by sound vibrations, their stereocilia bend, leading to the opening of mechanically gated potassium ion channels, causing depolarization.
• (D) In the knee-jerk reflex (a stretch reflex), the stimulus is the stretching of the quadriceps muscle, which is detected by muscle spindles, and the response is the rapid contraction of the same muscle.

Common Mistake: Students often confuse the roles of rods and cones in vision. Remember rods for 'night' (dim light) and cones for 'color' (bright light).

NEET Tip: For sensory organs, focus on the specific receptors and the type of stimuli they detect, as well as the mechanism of signal transduction.

Correct Answer: (C)