Question

Farmers need to apply less nitrogenous fertilizers to fields, if one of these plants are present

• A. Rhodophyceae
• B. Spirogyra
• C. Azolla
• D. Weeds

Answer 1

Answer: (C)

Azolla

Azolla serves as biofertilizer which refers to any living organism supplying plant nutrients directly or indirectly. Azolla is an aquatic fern that provide shelter to algae called as Anabaena in the cavities of its leaves. Anabaena fixes atmospheric nitrogen and thus, Azolla leaves serve as source of nitrogen which makes option C correct. Rhodophyceae is group of fresh/marine water red algae which are characterized by presence of phycoerythrin and phycocyanin; they are not present in crop fields; option A is incorrect. Spirogyra is a group of 400 species of free-floating green algae (division Chlorophyta) that are present in freshwater habitats and not in crop fields, option B is incorrect. The undesired plant species in between otherwise desired crop is termed as weed; it mostly harms the crop which makes option D incorrect.

Thus, the correct answer is option C.