Why are the Senate and House so different?
The US Congress is often referred to as a single entity, but it's actually a combination of two distinct groups: the House of Representatives and the Senate [1]. The framers of the Constitution knew it was important to protect the smaller states of the newly formed Union from being overshadowed by their more populous counterparts [2]. They hoped that by dividing legislative power between two houses, they'd be able to ensure equal representation for residents of all states [2]. 
The number of members of the House of Representatives is based on each state's population, while the Senate is composed of two members from each state [3]. Each chamber of a bicameral legislature has different powers, in order to ensure fairness through checks and balances within the system [3].
The main reason for the difference between the House and the Senate arises from the desire to protect the smaller states from being overshadowed by their more populous counterparts [1]. The framers of the Constitution hoped that by dividing legislative power between two houses, they'd be able to ensure equal representation for residents of all states [1]. 

The bicameral system (Congress) is composed of the House of Representatives and the Senate [2]. The House has more flexible rules than the Senate, allowing the minority to control the Senate [3]. There are 435 members in the House and 100 in the Senate [3]. The Constitution stipulates that for anyone to be a senator, he or she must be over thirty years old and lived in the country for about nine years; members of the House of Representative are over twenty-five years of age and must have resided in the United States for over seven years [4]. A senator serves for a six-year term while the representatives have a two-year term [4]. The shorter terms in the House are intended to make the representatives more responsive to the needs of the people [4].