Answer:
It converts modified epidermal cholesterol to a vitamin D precursor important to calcium metabolism
Step-by-step explanation:
Skin does not have it's own tissues for transporting material throughout the body. Those tissues would belong tot he circulatory system.
Glycogen is stored in the liver for use as energy.
Vitamin C is important for the immune system but is not absorbed through the skin. It's ingested.
The chemical process that makes vitamin d requires light to catalyze it. Humans make our own vitamin d using sunlight, which contacts our skin.