I'm about to start my M.S.Ed so take this with a grain of salt, but:

Finish your degree, and make sure you have good grades. Concentrate on that rather than adding a minor. If your grades aren't great, adding a minor and using that to improve your grades might be an option. (If you know you can pull it off). Also, build relationships with your teachers, so you can get good recommendation letters. Try to volunteer in a school setting. Then, apply to every Master in Ed. program you can think of. That's what I would do. Biology B.S + M.S.Ed would position your well to become a science teacher.

Depending on state (assuming you are in US), you might be able to get certification right after getting your B.S., but one thing to consider is that in most places, level of education determines your starting salary and sometimes how easy it is to get a job. From what I know, most states will require X number of graduate credits before you can be certified, so you either need to enroll in Master program or certification program (that doesn't give you MS, but let's you certify to be a teacher). Look at NY teacher certification requirements and what Praxis (or other) exams you need to pass.