Which one of the following is not true about rods?
**Core Concept**
Rods are a type of photoreceptor cell in the retina that are responsible for peripheral and night vision. They have a higher sensitivity to low light levels and are more numerous in the peripheral retina.
**Why the Correct Answer is Right**
Rods contain the photopigment rhodopsin, which is sensitive to low light levels. The absorption of light by rhodopsin triggers a signaling cascade that ultimately leads to the depolarization of the rod cell membrane. This is in contrast to cones, which are responsible for color vision and are more concentrated in the central retina. Rods do not contain the photopigments responsible for color vision, such as long-wavelength sensitive cones (L-cones) that are sensitive to red light.
**Why Each Wrong Option is Incorrect**
**Option A:** Rods are responsible for peripheral and night vision. This statement is true.
**Option B:** Rods do not contain the photopigments responsible for color vision. This statement is also true, as rods contain only rhodopsin and do not have the L-cones responsible for red vision.
**Option C:** Rods are more numerous in the central retina. This statement is false, as rods are more numerous in the peripheral retina.
**Option D:** Rods contain the photopigment rhodopsin. This statement is true.
**Clinical Pearl / High-Yield Fact**
Rods are responsible for peripheral and night vision, which is why individuals with rod-cone dystrophy often experience night blindness as a primary symptom.
**Correct Answer: C. Rods are more numerous in the central retina.**