Anabaena is a filamentous cyanobacteria; it is photosynthetic and it also can convert atmospheric nitrogen to ammonia via nitrogen fixation. It is often used for researching the beginnings of multicellular life due to its filamentous characterization and cellular-differentiation capabilities. Anabaena and most cyanobacteria are known for their ability to perform both photosynthesis and nitrogen fixation. Their cells contain heterocysts for nitrogen fixation, akinetes (spores) for survival, and chloroplasts for photosynthesis.
Chlorella is a genus of single-cell green algae belonging to the phylum Chlorophyta. It is spherical in shape, about 2 to 10 μm in diameter, and is without flagella. Chlorella contains the green photosynthetic pigments chlorophyll-a and -b in its chloroplasts. Through photosynthesis, it multiplies rapidly, requiring only carbon dioxide, water, sunlight, and a small amount of minerals to reproduce. The name Chlorella is taken from the Greek, chloros, meaning green, and the Latin diminutive suffix ella, meaning small. Many people believe Chlorella can serve as a potential source of food and energy because its photosynthetic efficiency can, in theory, reach 8%, comparable with other highly efficient crops such as sugar cane.
Chlamydomonas is a unicellular green algae and falls under the same phylum as Chlorella; Chlorophyta. These algae can be found all over the world; including soil, fresh water, oceans, and even on mountaintops in the snow. Algae in this genus have an interesting anatomy; they have a cell wall, a chloroplast, an “eye” that perceives light and two anterior flagella with which they can swim using a breast-stroke type motion. Chlamydomonas is frequently used as a model organism for research in cellular, molecular and genetic biology; all of it’s genomes have been determined and well studied.
Image 3. Chlamydomonas under a microscope
Haematococcus is a unicellular freshwater green algae that is a common component of nutraceuticals, pharmaceuticals, cosmetics, aquaculture, and numerous food products. It is also in the phylum Chlorophyta and is known to be an effective antioxidant and anti-inflammatory agent because it contains astaxanthin and other carotenoids. Haematococcus is a common and widely distributed species and can be found in small rock pools, cattle troughs, stagnant rainwater and ponds.
Image 4. Haematococcus under a microscope
Scenedesmus is also under the phylum of Chlorophyta and is a non motile and colonial green algae. This species is most often observed under the microscope to be in colonies of 4 cells arranged side by side (see pictures below). They have green chloroplasts and their cells contain pyrenoids which are their centers for carbon dioxide fixation. Scenedesmus is a freshwater species and is most commonly found in sewage ponds, and nutrient-rich lakes.
Image 5. Scenedesmus under a microscope
You can learn more about heterocysts here
and more about akinetes here