Except as otherwise set forth in the articles or bylaws, the board shall not have less than five directors, except that a cooperative with fifty or fewer members may have three or more directors as prescribed in the articles or bylaws. The directors of any cooperative organized under sections 351.1000 to 351.1228 may, by the articles or by the bylaws, be divided into such number of classes as set forth in the articles or bylaws. If the board shall be divided into classes, then the term of office of those of the initial first class shall expire at the first annual meeting of the members held after such classification becomes effective; of the second class, one year thereafter; of the third class, two years thereafter, and so on for each initial class; and at each annual election held after such classification becomes effective, directors shall be chosen for a full term, as the case may be, to succeed those whose terms expire, which terms shall, unless otherwise set forth in the articles or bylaws, be of a duration equal to the number of classes.