Short answers, pulled from the story.
Bicameralism is a system in which a legislature is divided into two separate chambers or houses, each with its own membership and powers. Unicameralism uses a single deliberating and voting body. Roughly 40% of national legislatures are bicameral, while 60% are unicameral.
The origins of British bicameralism trace to 1341, when the Commons met separately from the nobility and clergy for the first time, creating an upper and lower chamber. The upper chamber became known as the House of Lords from 1544 onward.
The Framers created a bicameral Congress to balance competing concerns. James Madison argued the Senate would act with more coolness and wisdom than the House, checking its "fickleness and passion". The Connecticut Compromise added a federal rationale: every state receives exactly two Senate seats regardless of population, while House seats are apportioned by population.
Perfect bicameralism requires a concurrent majority in both chambers to pass legislation, giving them equal power. Imperfect bicameralism allows one chamber to overrule the other; for example, the British House of Commons can override the House of Lords under the Parliament Acts of 1911 and 1949 if a bill is not passed within two sessions.
The Washminster mutation is a nickname used by political scientists to describe Australia's hybrid system, which blends the United States and Westminster models. Australia's Senate is a powerful upper house like the U.S. Senate, yet the country follows Westminster parliamentary conventions, including the confidence of the lower house as the basis for government.
As of the 16th of February 2021, 803 people sit in the House of Lords: 92 hereditary peers, 26 Lords Spiritual, and 685 life peers. Life peers are appointed either through the independent Appointments Commission or through Dissolution Honours at the end of each parliamentary term.