Question

Trichodesmium erythraeum, which imparts red color to seawater of the red sea is a
(a)Cyanobacterium
(b)Red algae
(c)Diatom
(d)Red coral

Answer 1

Hint: It belongs to a group of photosynthetic bacteria which are nitrogen-fixing and live freely in the soil or in a symbiotic relationship. They fix nitrogen into useful ammonium and nitrate form.

Complete answer:
The red sea is the saltiest, warmest, and red-colored sea around the world. Trichodesmium erythraeum belongs to the group of cyanobacteria commonly called blue-green algae. The cell wall is made up of several layers of mucoprotein and other polysaccharides but they lack cellulose and mannan which are the chief component of cell walls of red algae.
Trichodesmium also called sea sawdust blooms to appear brown when healthy and appear green when the blooms are starting to decay; It appears pink or red when certain pigments leak out of the cells.

Additional Information:
Trichodesmium is a diazotroph (that fix atmospheric nitrogen into a more usable form)
These are found in the nutrient-poor tropical and subtropical ocean waters. It is thought to be fixing atmospheric diatomic nitrogen into ammonium and nitrogen oxide. They fix nitrogen in daylight without the use of heterocyst. Other than nitrogen blooms of Trichodesmium also release carbon and another nutrient into the environment
Trichodesmium is present in colonial form and has a large degree of association with other organisms, including bacteria, fungi, and other groups.
So, the correct answer is, ’Cyanobacterium.’

Note: Diatoms are characterized by the presence of silica and minerals in their cell wall which is absent in Trichodesmium erythraeum.
The red algae secrete calcium carbonate shells which accumulate at the bottom of the sea forming red corals.