I know it's possible but don't have the information off hand so somebody else may be able to advise you better.
If you need 10 courses, you contact the department that offers the course. I.e. You need Chemistry? You contact the Chem department.
For seats in Life Sci courses, contact Sarah Robinson (
http://www.science.mcmaster. ca/lif.../contacts.html)
You do not have to take 10 courses, but you need 40 to graduate, unless you were planning to take summer school. You may also need it for some professional/grad schools which may require a full course load but that's really dependent on what you need