An alga, very rich in protein, is

Explanation

a. The alga that is known for being very rich in protein is Chlorella. Chlorella is a green microalga that is often used as a dietary supplement due to its high protein content and nutritional value. It is considered a good source of plant-based protein and is used in various forms, including powders and supplements, to provide essential amino acids and other nutrients. b.Nostoc is a genus of cyanobacteria, commonly known as blue-green algae. While it is a valuable component of aquatic ecosystems and plays a role in nitrogen fixation, it is not primarily known for its protein content. Nostoc can be consumed and is sometimes used in traditional cuisines, but it's not as rich in protein as Chlorella. c.Spirogyra is a type of filamentous green alga. It is not particularly known for its protein content, and it is not commonly used as a protein source. Instead, Spirogyra is often studied for its unique spiral chloroplast structure, which is a distinguishing feature. d. Ulothrix is another filamentous green alga. It is not typically regarded as rich in protein compared to Chlorella. Ulothrix is more commonly studied in the context of its morphology and life cycle.