Answer:
Because oxygen is the combustion fuel and glucose is the substrate needed for synthesis of energy as ATPs during cellular respiration.Therefore Guillermo lacks enough energy as ATPs in her body cells, especially skeletal muscles cells to complete the task of ascending the s steps.
For all the mitochondrial in cells(sites of energy production) to receive needed glucose,and other metabolites needed for energy synthesis; an efficient transport system is needed, so that these materials are available immediately, in required amount. This system is called circulatory system.
And for the the supply of combustion fuel (oxygen) needed for the completion of the ATP synthesis mechanisms; respiratory systems which convey oxygen from the external environments to the circulatory system through breathing mechanisms, for distribution is needed.
Thus the doctor needs to test both the circulatory and respiratory systems.
Explanation:
