hi,

see to study biology as optional subject you need to contact with your school authority, however while studying mpc at your state board you may apply for nios, nios stands for national institute of open schooling and its certificate is accepted in most of the university In India. so while studying your 12th course at  state board you may also enroll for nios.  however to write neet exam, you must study biology as compulsory subject in 12th course. so to study from nios from bipc stream would be good option.