Why are cones not as sensitive to light as rods?

• A. Each cone has more than one photopigment
• B. Cones respond to color, not brightness
• C. Each cone contains only one photopigment
• D. Rods are physically larger

Answer: (C)

In light sensitivity, how easily a photoreceptor can absorb photons and turn that into a signal matters more than color processing. Each cone cell contains only one photopigment, so the amount of pigment available to absorb light per cone is limited. In dim conditions, fewer photons are absorbed, making cones less likely to trigger a response. Rods, by comparison, have a higher capacity to absorb photons and, collectively, many rods feed into the same downstream cells, boosting the signal in low light. That combination lets rods be much more sensitive in dim illumination.

The other statements don’t capture why cones are less light-sensitive: one option suggests cones have multiple photopigments (they don’t per cell), another highlights color processing over brightness in a way that doesn’t explain sensitivity, and the last notes size without addressing pigment and signaling differences.