You choose what program you want to major in at the end of your first year, and then based on your marks, you may be accepted or not into these 4 choices you get.
Then before you pick your courses, you have to choose on of your accepted majors.
If you want to do biochem (biotech), then make sure you have all the first year admission requirements (found below)
http://registrar.mcmaster.ca /CALEN...13/pg1514.html