Dear aspirant,

As you have mentioned that you have taken mathematics in class 11th and as you have mentioned now currently you are in class 12th and now you are wanting to take up biology with maths.

So,let me tell you that I dont think any school will allow such a thing to do. In addition to that you will face problem because you have not studied biology in class 11th so you need to complete that also along with the 12th syllabus.

In entrance exams questions will asked from both 11th and 12th classes and if your base will be remain weak then you won't be able to clear the examination.

So, I recommend you to have final talk with your parents and the school authorities.