Question

The common phycobiont in a lichen is
a. Microcystis
b. Trebauxia
c. Ulothrix
d. Spirogyra

Answer 1

Hint: Lichens are composite organisms or entities which contain a permanent association of a fungus or mycobiont or an alga or phycobiont. The fungal partner is usually an ascomycete and sometimes a basidiomycete. The algal partner is mostly a green alga or a cyanobacterium.

Complete answer: The partner in lichen which enables photosynthesis is called a photobiont. Algal photosynthetic partners are called phycobionts, while cyanobacterial partners are called cyanobionts. About two thirds of all known lichens have phycobionts, and only one third have cyanobionts . The photosynthetic partners (photobionts) of lichens belong mostly to five distinct classes that are Cyanophyceae (prokaryotic), Trebouxiophyceae, Phaeophyceae Chlorophyceae (eukaryotic)

Among the given options:
Microcystis is a genus of freshwater cyanobacteria. It is presently the dominant bloom in freshwaters around the world. The cyanobacteria can produce neurotoxins and hepatotoxins, such as microcystin and cyanopeptolin in the water that make them poisonous for aquatic animals.

Ulothrix is a genus of green algae that belongs to the family Ulotrichaceae. It is a non-branching filamentous green alga, usually found in fresh and marine water. The cells of the alga are normally as broad as they are long, and they thrive in the low temperatures of spring and winter. They become attached to surfaces by a holdfast cell.
Spirogyra is a freshwater green alga found in shallow ditches, ponds and lakes. It is an unbranched, mucilage coated green filamentous alga which forms free-floating masses on the surface of freshwater bodies. It is also called water silk or pond scum.

Trebouxia is a unicellular green alga. It can either live in a symbiotic relationship with fungi in the form of lichen or it can survive independently as a free-living organism alone or in colonies. There are many types of phycobionts, though half the lichen associations contain various species of Trebouxia.

So, the correct answer is B.

Note: Although lichens usually appear to be single plant-like organisms, under a microscope their associations are seen to consist of millions of cells of algae (known as the phycobiont) woven into a matrix formed of the filaments of the fungi ( known as the mycobiont).