# Biomolecules from Microalgae and Cyanobacteria: Applications and Market Survey
## 2 Microalgae  
### What Are Microalgae and Cyanobacteria?  
According to phycologists, any organisms containing chlorophyll a (Chl a), devoid of stem, roots, leaves, and flowers, can be considered an alga [10]. These organisms are divided into macro- and microalgae, which are essentially differentiated by their sizes and organelle contents. Macroalgae are benthic, multicellular, and able to reach several meters in length, while microalgae are unicellular microscopic eukaryotic phytoplankton. There is a disagreement among taxonomists in classifying this polyphyletic group of organisms of prokaryotic microalgae, known as Cyanobacteria, as microalgae or bacteria [5; 6].  
There are obvious distinctions between Cyanobacteria and microalgae--primarily, the presence of membrane-bound structures in eukaryotic cells acquired during evolution through endosymbiosis [7; 11]. In fact, Cyanobacteria are primitive microorganisms that bear an intermediate structure between bacteria, characterized by the absence of a distinct membrane-bound nucleus, mitochondria, and chloroplasts, and plants by oxygenic photosynthesis. Secondly, eukaryotes are larger, more complex, more diverse, and can be either unicellular or multicellular [12], while prokaryotes are simple and microscopic single-celled organisms that have neither a distinct nucleus with a membrane nor other specialized organelles. Furthermore, Cyanobacteria contain chlorophyll a as a major photosynthetic pigment, which may be accompanied by carotenoids, xanthophylls, and phycobilisomes (mostly phycoerythrin and phycocyanin) as light collectors. It was estimated that around \(10^{25}\) cells of these blue-green microorganisms exist in the oceans, where they are responsible for the achievement of the fixation of photosynthetic carbon and nitrogen [13].  
Microalgae are able to grow rapidly and live in a wide range of environmental conditions [14]. They are closely guided by abiotic factors (light, salinity, pH, temperature, and trophic limitation or excess) and biotic ones (trophic relationships) [15]. Microalgae generate themselves using photosynthesis by capturing sunlight, H\({}_{2}\)O, CO\({}_{2}\), and inorganic nutrients and converting them into biomass, chemical energy, and O\({}_{2}\), effectuating a full life cycle every few days [16]. They are more efficient at utilizing sunlight than terrestrial plants (10 times greater), with numerous additional technological advantages such as consuming damaging pollutants, having minimal resource requirements, and not competing with agriculture for precious resources [8].  
The presence of microalgae is essential since they represent the basis of several food chains. It is estimated that microalgae and Cyanobacteria are around 200,000 to 800,000. Among them, the sole diatoms are estimated to be over 200,000 [17; 18; 19]. Currently, more than 164,800 species and intraspecific names exist in the database Algaebase ([[https://www.algebase.org/](https://www.algebase.org/)]([https://www.algebase.org/](https://www.algebase.org/)), accessed on 24 november 2020). This appreciable diversity is associated with richness in lipids, proteins, vitamins, pigments, carbohydrates, and other compounds.