Answer:
The Circulatory System
Explanation:
When blood is rich in carbon dioxide it leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs. (All of which have to do with the circulatory system)
c proteins .. most used cuz it provides energy and builds muscle
UV rays reacting with the O2 molecules
I might be wrong a little but
Hope the helps :)
I would say communication, as neurons transmits messages from one part to another part of the body
Because proteins are complex molecules, the body takes longer to break them down
