Except for regulations applicable during an emergency, as that term is defined in section 1733.01 of the Revised Code, and except that the articles or regulations may require a greater number, a majority of the entire authorized number of directors is necessary to constitute a quorum for a meeting of directors except that a majority of the directors in office constitute a quorum for filling a vacancy on the board. The act of a majority of the directors present at a meeting at which a quorum is present is the act of the board, unless the act of a greater number is required by the law, the articles, regulations, or bylaws.