Whenever bonds or notes are issued by the state board of regents, it shall be the duty of said board to establish, impose and collect rates, fees or rentals for the use of and services provided by the residence halls and dormitories, including dining and other incidental facilities therefor, at the institution on behalf of which such bonds or notes are issued, and to adjust such rates, fees or rentals from time to time, in order to always provide net amounts sufficient to pay the principal of and interest on such bonds or notes as the same become due and to maintain a reserve therefor, and said board is authorized to pledge a sufficient amount of the net rents, profits and income derived from the operation of residence halls and dormitories, including dining and other facilities therefor, at such institution for this purpose. Rates, fees or rentals collected at one institution shall not be used to discharge bonds or notes issued for or on account of another institution. All bonds or notes issued under the terms of this subchapter shall be exempt from taxation by the state of Iowa and the interest thereon shall be exempt from the state income tax.