What are the effects of party system?

Answer 1

1 - Typically whichever party holds the Majority of members in either house (i.e. House of Representatives or Senate), they establish the number of members that sit on each of the standing committees.

And you can safely say that they will set it up so that there are more members of the majority party than not. For example, let's say there are 21 members on the House Transportation committee. Odds are, at least 11 members will be Democrats (since they hold the majority in the House) and the remaining members will be Republicans. This is to make sure that the majority party (if they keep all of their members in line) get to decide what policy will be.

2 - All Committee Chairperson are appointed by the Speaker of the House/Majority Leader of the Senate (depending on which House you're talking about). It is clear that those chairs are going to be from the same party as the Speaker.

Committee Chairpersons control the agenda and dictate when committees meet, what they talk about, and when they vote. That is a lot of power in the committee system.