Controls the chemical environment around neurons in the cns

the answer is:

carbon dioxide

im not intirely sure but i think the anwser is d relative humidity

food source and hunting?

in addition to being able to metabolize, grow, digest food, and excrete wastes, what other functions must an organism perform if it is to survive? survival also depends on the ability to maintain one's boundaries, to move, to respond to stimuli, and to reproduce. oxygen is a survival need.