You absorb vitamin d from sunlight shining on your skin.
Vitamin d can help the absorption of calcium, which is capable for strengthening your bones and teeth.
Therefore if u r lacking of vitamin d, your bones and teeth may be soft, and especially among children, you may get ricket, where the legs are bent outwards.
Carbon dioxide and photosynthesis
Oxygen breakdown the food and release energy molecules as ATP
Cell, Tissue, Organ, Organ System
(Hope this Helps)
I believe the answer you are seeking is feedback loop
