**1. Introduction**

256 Artificial Photosynthesis

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Phytoplankton cells are ideal organisms for the study of various aspects of photosynthesis, since most of their cells are devoted to components related to the harvesting of light energy and its storage as high energy compounds. They lack flowers, roots and all of the many structures and mechanism evolved in the course of the emergence of plants from the primordial oceans and conquering land. The products of photosynthesis are synthesized while carbon from assimilated CO2 is being reduced and oxygen from photolytically split water is evolved. In most open water bodies – freshwater and marine – the energy input of the entire ecosystem depends on microscopic free-floating photosynthetic organisms- the phytoplankton. The determination of phytoplankton biomass and its photosynthesis activity is a great interest to ecologists.

The photoacoustic method allows the direct determination of the biomass of different taxa of phytoplankton and the efficiency of their photosynthesis. The latter is accomplished by relating the energy stored photochemically by photosynthesis to the total light energy absorbed by the plant material.

The method yields rapid, direct results of the efficiency of photosynthesis, compared to standard measurements based on 14 C fixation and oxygen evolution, or compared to indirect results from measurements of variable fluorescence.

We review the history of the application of photoacoustics to photosynthesis research. Our results show that the pulsed photoacoustic technique provides direct information on the biomass and phytoplankton photosynthesis and demonstrate its application in the study of phytoplankton ecology and physiology and in basic research of their photobiology.

The photoacoustics has a high potential for following the effects of environmental parameters such as irradiance, nutrient status and pollution on phytoplankton communities and their photosynthetic activity.
