A word of warning. If you're looking to study biology or chemistry at university you'll need to take maths for your highers. Both subject areas rely heavily upon advanced mathematics. (When I was studying for my maths degree I got fed up of constantly having to help the biology students with their maths, despite the fact that they'd all taken maths for their A-levels or Highers. Chemistry requires even more maths).
In fact nearly all sciences at university have a fairly high reliance upon mathematics, so you'll either need to commit yourself to studying it at Higher level or to rethink your university options. (You won't be accepted for any university course in chemistry or biology without Higher maths. You'll also be rejected from most other science-based courses).
Assuming that you don't take maths, and depending upon what's available at your school, you might like to consider Sociology, Psychology or Philosophy for your final subject choice.
Chris