  Signal transduction, or signal-processing capability, is a fundamental
property of nature that manifests universally across systems of different
scales -- from quantum behaviour to the biological. This includes the detection
of environmental cues, particularly relevant to behaviours of both quantum
systems and green plants, where there is neither an agent purposely
transmitting the signal nor a purposefully built communication channel. To
characterise the dynamical behaviours of such systems driven by signal
detection followed by transduction, and thus to predict future statistics, it
suffices to model the flow of information. This, in turn, provides estimates
for the quantity of information processed by the system. The efficiency of
biological computation can then be inferred by measuring energy consumption and
subsequent heat production.
