I must appreciate your stamina in the sense you are still trying to make your career with the selection of Biology in your 10+2 stage though you have cleared your class twelve in 1997. This shows how passionate you are for going ahead for the course of Biology.
Though this is not so difficult if you have the time for the persuasion of class twelve Board with the distance course such as IGNOU, Kota Open University, Manipal Distance Education, Utkal University Distance Education and many more.
However, to have the enriched knowledge in Biology without wasting your time in searching out appropriate course materials, you can contact IGNOU officials for the selection of your course taking Biology, Physics, Chemistry, English and Hindi. Follow the course materials in your convenient timing and secure the degree afresh with IGNOU. Moreover any doubt cropping up in your mind be clarified in their contact session organised in the different study - centres. Hence joining IGNOU makes sense while other open universities lack such facilities.
If you desire to pass with the single subject Biology only, talk to the officials so that your request is entertained.