The body needs what in only small amounts, but these organic molecules are an important part in perform cellular reactions?

Vitamins

Explanation:

Vitamins are the organic compounds that are needed by body in small amounts. Most of the vitamins are not synthesized in human body and should be supplemented with food. Vitamins serve as coenzymes or part of coenzyme which are required for the activity of respective enzymes. Hence, vitamins an important part in helping perform cellular reactions.

correct answer is option a.

tropopause, stratopause and mesopause have all in common aspect that is point of maximum temperature in its layer of the atmosphere. all layers of atmosphere observe abrupt change in temperature. tropopause is the boundary between troposphere and stratosphere. stratopause is the boundary between stratosphere and mesosphere. mesopause is the boundary between mesosphere and thermosphere. these all boundaries are ranges between altitude of 0 to 80 km.