Question

1. In humans, darker skin color is adaptive at latitudes near the equator (where ultraviolet light is most intense) because UV light

stimulates synthesis of folic acid 

causes breakdown of folic acid 

stimulates synthesis of vitamin D 

causes breakdown of vitamin D

2. In humans, lighter skin color is adaptive at latitudes far from the equator because UV light

stimulates synthesis of folic acid 

causes breakdown of folic acid 

stimulates synthesis of vitamin D 

causes breakdown of vitamin D

Answer 1

A common explanation to both the answers -

The difference in skin color within poles and equator is due to the changes in the intensity of the sunshine in both regions. melanin is a pigment that protects the skin against the harmful UV rays in sunlight. Sunlight is the cause of the sunburns and overproduction of vitamin D. To protect our body from these sunburns, and from the increased production of vitamin D, the melanin pigment is formed. The melanin pigment gives a brownish-black pigmentation to the skin. As we know the equator gets more sunlight with higher intensity and in poles, the sunlight is relatively lesser or not there, hence those at the equator gets more melanin pigmentation as a protective system. while those at poles get a lighter colour.

UV rays from the sun can cause degradation of the folic acid. hence those peoples at the equator will be more prone to degradation of the folic acid compared to those living in the poles. While those at poles develops folic acid.

Hence answers are -

1) Answer - causes breakdown of folic acid, stimulates synthesis of vitamin D.

2) Answer - stimulates synthesis of folic acid, causes breakdown of vitamin D.