In NIOS there is the facility of On Demand Examination, in which you can attempt for the subjects which you haven't given in your boards examination but as a separate subject you can write it in NIOS. The NIOS will issue the certificate & Marksheet for only that subject. Now you can use both the certificate of NIOS & your council/Board & can take admission in course where Biology is required to be a subject compulsorily.

For more information regarding NIOS you can consider the link below:

https://school.careers360.com/exams/nios-class-12

I hope this helps. Wish you a great eve!