Coherence can provide functional advantage. In the field of quantum technologies, quantum computation algorithms use coherence to beat classical algorithms, while quantum protocols secure communications thanks to coherence. In classical optics, coherent light can be tightly focused, providing resolution in imaging or surgery applications. What about coherence in living systems: is classical or quantum coherence playing a role in biology? Does it provide functional advantage? Are living systems actively preserving the coherence of some degrees of freedom? This internship/PhD thesis aims to explore these questions at the level of a single live cell, using the tools of quantum optomechanics, which enable unprecedented sensitivity and time-resolution. In the last years, our team carried the first optomechanical experiments on biological objects, albeit in a dry environment where the biological functions were turned off. More recently, we immersed optomechanical experiments in a physiological liquid medium in order to measure a living object in action, when biological mechanisms are this time turned on. Building on this approach, the project will investigate active biological mechanisms in the cell and link them to the capacity to sustain or degrade the coherence of mechanical and optical degrees of freedom, hence exploring a practical interface between quantum science and biophysics.