Hello,

The basic requirement is to have graduation in any field and if you are fulfilling that requirement then you are free to apply for civil services exam. You can start your preparation and give your best. Here is the link to some information about exam.

https://competition.careers360.com/articles/upsc-ias/amp

Yes,you can appear UPSC CSE after BSc Biology. It will be helpful if you opt Biology as your optional subject .The basic requirement for appearing in this examination is that you must have to graduate from any stream. UPSC welcomes all graduates who are interested in civil services.

Hope this helps