As noted, it depends, but also note that many courses, particularly in STEM, use multiple factors to determine grades. You will have the major tests, usually three in the semester, which will account for the majority of your grade, but you will also have frequent quizzes and homework which also account for a portion of your grade and thus you can more or less help yourself in getting a higher grade by doing all the homework and getting it correct; of course you can also lower your grade by blowing off homework.