  We outline a framework for describing photo-activated biological reactions as
generalized quantum measurements of external fields, for which the biological
system takes on the role of a quantum meter. By using general arguments
regarding the Hamiltonian that describes the measurement interaction, we
identify the cases where it is essential for a complex chemical or biological
system to exhibit non-equilibrium quantum coherent dynamics in order to achieve
the requisite functionality. We illustrate the analysis by considering
measurement of the solar radiation field in photosynthesis and measurement of
the earth's magnetic field in avian magnetoreception.
