What things can a doctor do which a nurse cannot do to help patients

eg. prescrbing? , diagnosing?

Doctors can prescribe drugs, which nurses cannot (although in most states, a nurse practitioner can do this also). Doctors plan the managment of the patient, and nurses generally carry out the plan day to day and act as a patient advocate. Doctors can perform surgery. Nurses may assist, but do not control the surgery. Certain other procedures may only be performed by a doctor (central lines, lumbar puncture). Many specialties are available in both fields, but surgery, radiology, anesthesiology (except for CRNP's), and many others are closed to nursing.