do science students have to take biology?

I don't think so.
But all your course requirements can be found on the McMaster Course Calendar

http://registrar.mcmaster.ca /CALEN...nt/pg1466.html

In first year you would most likely have to take introductory bios. If you are talking about the life science program, I don't think you can avoid biology courses.

It depends which program in "science". Math & stats students are considered science students but they certainly don't. Can you be more specific than just "science"?

Or look it up in the course calendar yourself if you are uncomfortable posting your program.