Q.49 Which of the following algae are used as bio-fertilizers?
1. Spirogyra, Gloiopeltis, Ulothrix
2. Ulothrix, Chara and Anabaena
3. Anabaena, Azolla, Nostoc
4. Nostoc, Volvox, Anabaena
Anabaena, Azolla, and Nostoc serve as key biofertilizers in agriculture, especially rice paddies, due to nitrogen fixation. NEET Q.49 tests identification of nitrogen-fixing cyanobacteria and associations used sustainably. Option 3 provides the precise match.
Correct Answer
Option 3. Anabaena, Azolla, Nostoc represents proven biofertilizers. Anabaena and Nostoc fix atmospheric nitrogen as free-living or symbiotic cyanobacteria, while Azolla hosts Anabaena azollae in a symbiotic association boosting rice yields by 20-30%.
Option Breakdown
Options mix nitrogen-fixers with non-fertilizer algae, testing algal classification knowledge.
| Option | Algae Listed | Biofertilizer Status | Reason |
|---|---|---|---|
| 1 | Spirogyra, Gloiopeltis, Ulothrix | Incorrect | Filamentous greens; no N-fixation; Spirogyra lacks heterocysts. |
| 2 | Ulothrix, Chara, Anabaena | Incorrect | Ulothrix/Chara (greens/charophytes) not used; only Anabaena qualifies. |
| 3 | Anabaena, Azolla, Nostoc | Correct | All N-fixers: Anabaena/Nostoc free-living; Azolla pinnata + Anabaena symbiotic for rice. |
| 4 | Nostoc, Volvox, Anabaena | Incorrect | Volvox (colonial green) lacks N-fixation; Nostoc/Anabaena valid but incomplete. |
Option 3 uniquely lists all functional biofertilizers applied in wetland crops.
Biofertilizer Roles
These algae enhance soil nitrogen without chemicals, aligning with sustainable agriculture.
Anabaena
Forms heterocysts for N2 fixation; associates with Azolla; used in rice fields.
Azolla
Fern pinnata pinnata hosts Anabaena azollae; green manure adds 40-80 kg N/ha.
Nostoc
Free-living cyanobacterium; fixes N in rice paddies and uplands; produces biomass.
This reinforces cyanobacterial ecology for NEET microbiology and environmental biology sections.
