ABSTRACT
I. INTRODUCTION A. General Scientific Features The nuclear reaction that takes place deep inside the sun consists of the fusion of hydrogen (H2) to helium (He). According to up-to-date estimates about 5 109 kg of molecular hydrogen is converted every second with the difference in the masses of the involved molecules being emitted as radiation equivalent to approximately 6000 K photons. The resulting energy can be calculated to a value of 1400 kW m2. Per year, this process supplies earth with the immense energy amount of 56 1023 J. Even under the assumption that about 50% of the radiation might be reflected by clouds and gases of the atmosphere (thus not reaching the earth’s surface) and that 50% of the passing radiation is in the long-wavelength region with a low energy content (e.g., infrared), energy of about 14 1023 J is available. This gigantic amount, however, is “mere” radiation energy, which cannot be readily used by (nearly) any biological organism. Only one type of organism is capable of converting this abiotic energy into a biologically useful form, and consequently these organisms are called photoautotrophs. Among these are cyanobacteria, green algae, photosynthetic bacteria, and higher plants.
