For maths GCSE I got a B and a C. I hated maths and did not think I was good at it and was very surprised I passed, I chose biology and chemistry as 2 of my a levels.
Biology- very simple, no need to worry about this, especially for AS. I have heard A2 becomes more complex but not too bad.
Chemistry- from experience I hated chemistry a level anyway (now dropped it), which may have influenced my view on its maths content. It contained a lot more than I thought which threw me off. In our mock I would say at least 50% was maths calculation based, particularly manipulating formulas.