Answer:
I think it just all exists at once, if it never is created or destroyed. It must have just appeared at the same time at some point. It doesn't exactly come from anywhere, but that's my opinion. There might be another scientific answer out there, but that's what i think. I hope this helps.
Explanation:
Sebum, a fatty substance that serves as a water repellent it also serves as a natural antibacterial and antifungal agent,
yes the skin is important not only to excrete but its also a protective organ that absorbs oxygen and nitrogen
Functions of cell surface Receptors .
most ligands responsible for cell-cell signaling ( including neurotransmitters, peptide, hormones, and growth factors) bind to receptors on the surface of their target cells.
