Biology has mathematics in it as well, involving calculus. You'll usually explore this when you take further university level studies in Biology. You don't cover the maths in HSC Biology because you're not expected to know how to use calculus in HSC science courses.
In fact, there is a 3rd year Applied Maths course offered at USyd called Differential Equations and Biomathematics (probably something similar may be offered elsewhere). I quote from their unit outline: (
https://ssa.usyd.edu.au/ssa/handboo...ex=175860&session=1&academic_year=2008&back=1)
"The applications in this unit will be drawn from predator-prey systems, transmission of diseases, chemical reactions, beating of the heart and other equations and systems from mathematical biology."
So yes, virtually all areas of science (even social science) has mathematics in it. There is no escape from mathematics
.