at the tissue level at the organ level at the system level at the cellular level
I gave my students this multiple choice question: When athletes begin to exercise, their heart rates and respiration rates increase. At what level of organization does the human body coordinate these functions?

Only one answer is correct among these 4 choices:
- at the tissue level
- at the organ level
- at the system level
- at the cellular level

Could you tell me which one is correct?

at the system level