Photosynthesis Converts Inorganic Compounds to Organic Matter

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Introduction

Photosynthesis is a process done by photoautotrophs to convert inorganic compounds and light energy to organic matter. In all photosynthetic organisms, organic pigments exist to harvest the light energy. The three major classes of pigments are chlorophylls (green pigments) and carotenoids (yellow or orange pigments) which are lipophilic and associated in Chl-protein complexes as well as phycobilins that are hydrophilic. All chlorophylls (a, b, c and d) have two major absorption bands: blue or blue-green (450 or 475 nm) and red (630-675 nm). Chl a is present in all oxygenic photoautotrophs as part of the core and reaction centre pigment-protein complexes, and in light-harvesting antennae, it is accompanied by Chl b or Chl c. The accessory (antennae) pigments Chl b, c and d extend the range of light absorption. Carotenoids, a large group of biological chromophores, with an absorption range of 400-550 nm, have several roles in photosynthesic apparatus, such as being accessory light-harvesting pigments transferring excitation to Chl a, structural entities within the light-harvesting and reaction center pigment-protein complexes, and molecules required in the protection against excess irradiance. There are different types of microalgae, however only Chlorella sp. and Spirulina sp. are considered in the experiment as follows:

Chlorella sp. a green microalgae come from Chlorophyta division, or green algae, which embrace a large group of organisms with a great morphological variability, ranging from microscopic to macroscopic forms. Classes in Chlorophyta division have chlorophyll a and b and several carotenoids, that may be synthesized and accumulated outside the chloroplast under conditions of nitrogen deficiency and/or...

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...c microorganisms grow inside the flask due to the human errors, led to the possible later decrease in PAR*Y value after complete reduction of PSII.

Conclusion

Comparing the values of specific growth rates in six different growth and nutritional conditions (see table ), Chlorella sp. growing mixotrophically in light condition, supplied with acetate, shows the highest specific growth rate, after which Chlorella sp. growing heterotrophically in dark condition and supplied with acetate, and Spirulina sp. growing mixotrophically with acetate as the supplement are the second and the third highest in specific growth rate, respectively. Therefore, a mixed autotrophic and heterotrophic (mixotrophic) culture is preferable, however a heterotrophic culture is still suitable to both Chlorella sp. and Spirulina sp. showing a faster growth rate compared to autotrophic cultures.

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