What subject? Is it it could be for anything
The primary role of the respiratory system in living organisms is B. TO OBTAIN OXYGEN.
Through the process of breathing, we inhale oxygen and exhale carbon dioxide. Oxygen is then transported by our blood to be distributed to the various parts of our body in order for these parts to function properly.
The absence of oxygen in the body will result to the gradual decline and death of our cells. When our respiratory system is compromised, it affects how our brain and heart function and may cause lasting damage if not quickly resolved.
I think it's PHOTOSYNTHESIS because plants require water also during this process.