Mathematical biology is a subfield of biology that uses mathematical means to investigate and describe biological systems. It covers all levels of hierarchical organization of life and draws on methods from all major branches of mathematics. For example:
The application of mathematics to cellular and molecular biology is so pervasive that it often goes unnoticed. The determination of the dynamic properties of cells and enzymes, expressed in the form of enzyme kinetic measurements or receptor-ligand binding are based on mathematical concepts that form the core of quantitative biochemistry. Molecular biology itself can trace its origins to the infusion of physical scientists into biology with the inevitable infusion of mathematical tools. The utility of the core tools of molecular biology was validated through mathematical analysis. Examples include the quantitative estimates of viral titers, measurement of recombination and mutation rates, the statistical validation of radioactive decay measurements, and the quantitative measurement of genome size and informational content based on DNA (i.e., base sequence) complexity. 
- Cohen JE (2004) Mathematics Is Biology's Next Microscope, Only Better; Biology Is Mathematics' Next Physics, Only Better. PLoS Biol 2(12): e439.
- Simon A. Levin SA (Workshop Organizer and Editor) MATHEMATICS and BIOLOGY: THE INTERFACE | Quote from: Chapter2: The Impact of Mathematics on Cellular and Molecular Biology.