Question

The largest algae is
A. Laminaria
B. Macrocystis
C. Nereocystis
D. Sargassum

Answer 1

Hint: Giant kelp is the largest algae. They are the largest of all marine algae. These organisms live in cold water where they can form large, dense kelp forests that provide habitat for other marine species.

Complete answer: Macrocystis is a genus of large brown algae. This genus has the largest algae of all Phaeophyceae. Giant bladder kelp (Macrocystis pyrifera) is the largest alga species measuring up to 65 metres. Macrocystis has pneumatocysts at the base of its blades. It is commonly present along the coast of the eastern pacific ocean. They are harvested as a source of alginate, a gel-like substance with a number of industrial and biomedical applications. Laminaria is also a genus of 31 species of brown algae. It is relatively larger but smaller than macrocystis. It is a source of iodine, which is commonly used to promote thyroid health. Mannitol extracted from Laminaria is used to decrease high intraocular pressure, and to lower excessive intracranial pressure. Nereocystis is a genus of subtidal kelp commonly called bull kelps. They grow in deep waters and rapid tideways and can attain length up to 40 metres. Gulfweed (Sargassum) is common as free-floating masses in the gulf stream and sargasso sea. It is used as natural fertilizers and herbicides to improve the harvest of corn, squash, chilli and beans.
Hence, the correct answer is option is B.

Note: Algae constitute a polyphyletic group since they do not have a common ancestor, and although their plastids seem to have a single origin from cyanobacteria, they were acquired in different ways.