Base your answer on the investigation described below and on your knowledge of biology. As part of an investigation, 10 bean seedlings in one setup were grown in the dark, while 10 seedlings in another setup were grown in sunlight. All other growth conditions were kept the same in both setups. The seedlings grown in the dark were white with long, slender stems. These seedlings soon died. The seedlings grown in the sunlight were green and healthy. Which hypothesis was most likely being tested in this investigation?
A. Plants grown in the dark cannot perform the process of respiration.
B. Sunlight is necessary for the normal growth of bean plants.
C. Light is necessary for the germination of bean seeds.
D. Light is necessary for proper mineral absorption by plants.

In the investigation, sunlight was the only factor that was varied between the two group of seedlings. Hence, the observed differences in the behavior and appearance of the seedlings can be said to be due to the effect of sunlight.

Sunlight is necessary for the normal growth and functioning of plant as it drives some important physiological processes within the plant's body. These processes include but not limited to;

Photosynthesis
Chlorophyll synthesis

Without light, plants will not be able to carryout photosynthesis which is the only way through which plants can get energy for their proper function. Light is also needed in the biosynthesis of chlorophyll, a substance that gives plants their green colour. Without light, plants will general appear off-green because of lack of chlorophyll.

Hence, plants deprived of light will gradually grow thinner and whiter (etiolation) till they eventually die.

The correct option is B.