Biological function as quantised organised action

Biological systems often realise function through restricted repertoires of persistent states and reproducible trajectories, despite operating far from equilibrium under noise and dissipation. This paper develops a mesoscopic theory for such discreteness in functionally closed biological systems. A functional act is defined as a thermodynamically open episode over an operational time window \(=t_2-t_1\), during which all participating domains remain engaged in the same regulated process. The internal entropy-production rate \(σ(t)\) measures the irreversible cost of this organised activity. Exact extensivity of \(σ(t)\) across operationally simultaneous domains makes this cost positive and composable over the act. The resulting act-level dissipative action, \(≡(σ;)\), is not a microscopic quantum or universal constant, but an act-dependent resolution scale for distinguishable functional realisations. Functional closure supplies the corresponding global action invariant, \(\), whose admissible values become discrete, \(=n\). The resulting functional states are closure-compatible, dissipatively resolved realisations of organised biological action. The theory predicts resolution thresholds and clustering of trajectory ensembles in action-like observables, with loss of discreteness when closure, operational simultaneity or dissipative resolution fails.