Each of the 338 members of Parliament in the House of Commons is elected by simple plurality in an electoral district or riding. General elections must be called by the governor general, either on the advice of the prime minister or if the government loses a confidence vote in the House. The ''Constitution Act, 1982'' requires that no more than five years pass between elections, although the ''Canada Elections Act'' limits this to four years with a fixed election date in October. The 105 members of the Senate, whose seats are apportioned on a regional basis, serve until age 75.