The legislative branch is also referred to Congress at the federal level in the United States. The two parts of the legislative branch are the House of Representative and the Senate.
The Constitution determines the length of the terms for the members of the House of Representatives and the Senate. Representatives are elected for two years terms. This is so they can be more closely tied to the desires of their constituents. The number of Representatives each state has is determined by population. Senators are elected for six years terms. Each state has two Senators as outlined in the Constitution.