Two samples from a biologically active system, Trunculariopsis trunculus, were used in thick film form: one damp and the other dry. In both cases intense and broad absorption bands appeared in the visible region of the electromagnetic spectrum near yellow, as well as below 330 nm, attributed to charge transfer transitions. The damp sample produced a higher response signal at about 570 nm. The Photo-acoustic spectra contain all the bands of radiation vital for maintenance of activity in a living system with a distinctive prominence of the yellow part of the spectrum. © 2007 Elsevier B.V. All rights reserved.