Final answer:
The term used when describing the EMT's responsibility to act on behalf of the patient when they are unable to do so is Patient advocate.
Step-by-step explanation:
The term used when describing the EMT's responsibility to act on behalf of the patient when they are unable to do so is Patient advocate. An EMT serves as the patient's advocate by representing their best interests and ensuring they receive proper care and treatment. This could involve making decisions on the patient's behalf or advocating for their needs.