Question

A red flower looks black in the evening because of
A. Change in flower colour
B. Functioning of rods only
C. Beginning of colour blindness
D. Absence of cones

Answer 1

The human eye can see the different colors either bright or dull like black and white. The rods and cones in the retina of the eye make it possible to detect colors in dim and normal light respectively. These cells function based on the light conditions provided to them.

Complete answer:
The eye consists of an internal layer of photoreceptor cells embedded in the region called the retina. The retina is the key part of the eye that enables us to detect colors and pictures in our surroundings. This is possible due to photoreceptor cells in the retina which absorb the reflected light from objects in surroundings. The retina contains two types of photoreceptors, these are called rods and cones. The rods help in visualizing the surrounding in dim light or night light like in the evening. On the other hand, the cones help in visualizing the surrounding in normal light or daylight like in the morning.
Now, the cones have a protein called photopsin which is of different types for different color absorption. The cones can detect green, red, and blue colors. The photopsin present for the red color is called erythrolabe. The erythrolabe absorbs the reflected light from the flower which has the frequency of red light due to which flower appears red. But in the evening, the cones cannot function. Rods function in the evening due to dim light. They can visualize objects as black or white only. When light reflects from the flower in the evening, it appears black due to the functioning of rods only.
Thus, the right answer is option B.

Note: The light-absorbing opsins present in rods are called rhodopsins. They can detect objects in dim light. The phenomenon above described is not related to the absence of cones as cones cannot be absent in a normal eye. The cones are just switched off in the less light conditions.