I am writing a differed exam for a course that is a prereq for a required course i sem 2. Do I need to drop the second semester course? I would call the office of the Registrar, but they are closed and I would really like the answer asap!

As long as your grade on the final would not determine if you pass or fail, you can still take the 2nd course. However, I would not recommend this, especially if there's even a slight chance you deferred due to unpreparedness (not sickness, family emergencies etc).

With something like Chemistry, or the first year Kin's, or Math, they all build on each other. If you're not sure about whether you are comfortable with the material, drop the second term course and retake it next year. If you are in a position to fail the course based on your exam and don't do as well as you'd like (very rarely do deferrals go well; people usually struggle with 6 courses), that is a precarious position to be in

The university assumes you're passing until you fail for sure. So, you can take it.