Dear Student,

As of a mathematics stream student who have no idea about the biology you can refer:

• Nootan ISC 11th and 12th.
• NCERT biology for 11th and 12th.

these book are enough and covers all the topics that can appear in the test paper for biology section. And I am hoping you have studied well in physics and chemistry as they have the same topics form 11th and 12th standard that you have already covered in your intermediate.