Uh it might just be me but the maths in Biology is pretty hard. Not that the skills needed is difficult but understanding what the question is asking of you. Plus the fact that there is more of them now than before.
I don't think it's impossible with your grades but you might want to do a lot of extra reading. Personally i got an 8 in GCSE Maths and i do both A Level Maths and Further Maths and i still lose most of my marks in Biology on the maths questions.
It might just be me though.