Dear aspirant,

The difficulty of a course is heavily dependent on the interest of the person who is pursuing the course. If you are interested in microbiology and biology in general, you will find it easy.

Generally, you will have the time to pursue another course in the side only if you aren't looking for opportunities in microbiology after graduation. For getting a job/higher studies opportunities in microbiology, you will have to do more than just the coursework. You might have to look for internship opportunities, industry internship opportunity, research work, extra lab work, additional research articles reading.

If that's not what you want to do, then yes, you can do something else in the side while pursuing BSc microbiology and meeting the course requirements decently.