ABSTRACT
Microalgae include the prokaryotic groups: cyanobacteria, prochlorophytes and eukaryotic groups: glacophyta, chlorophyta, rhodophyta, chromophyta, dinoflagellates, euglenoids and others. The prokaryotic microalgal cell microalgae have a peptidoglycan cell wall, simpler photosynthetic apparatus, phycobilins as accessory pigments, but lacks membrane-bound organelles, naked genetic material and simpler photosynthetic apparatus. The eukaryotic cell is characterized with rigid cellulosic cell wall, equipped with membrane-bound organelles such as nucleus, chloroplast, mitochondrion and golgi apparatus.
Most of the microalgal groups are obligate photoautotrophs, needing sunlight as an energy source to convert inorganic entities in to organic compounds; but there are some species which also follow amphitrophic or mixotrophic growth in certain conditions like dark conditions. Since the Great Oxygenation Event (GOE), cyanobacterial oxygenic photosynthesis plays an important role in nutrient cycling through carbon fixation. The microalgae uptake and transport of the nutrients in their desired form like nitrogen in nitrate, nitrite, urea or ammonium; phosphorous in orthophosphate, phosphate; sulfur in a sulfate form. Before assimilation, all nitrogen forms convert into ammonium before their assimilation, while phosphorous and sulfur forms usually assimilate uptake forms. Some nutrients like phosphorous involve luxury uptake and are stored as polyphosphate granules. Microalgal cell structure, nutrition and metabolism have been discussed in this chapter.
