Prelims 2013 · archive
EasyConsider the following organisms:
- 1.Agaricus
- 2.Nostoc
- 3.Spirogyra
Which of the above is/are used as biofertilizer/biofertilizers?
Answer & explanation
Answer: (b) 2 only
Only Nostoc is used as a biofertiliser. It is a nitrogen-fixing cyanobacterium, and cyanobacteria serve as an important biofertiliser in paddy fields. Agaricus is a mushroom grown as food, and Spirogyra is a filamentous green alga that is not used as a biofertiliser.
- ✗ 1. Agaricus includes the white button mushroom (Agaricus bisporus), a Basidiomycete fungus cultivated as food. It is not used as a biofertiliser.
- ✓ 2. Nostoc is a cyanobacterium that can fix atmospheric nitrogen. In paddy fields, cyanobacteria serve as an important biofertiliser.
- ✗ 3. Spirogyra is a filamentous green alga belonging to Thallophyta. It does not fix atmospheric nitrogen and is not used as a biofertiliser.
Remember · Biofertilisers come from nitrogen-fixing bacteria (Rhizobium, Azotobacter), fungi (mycorrhiza) and cyanobacteria (Nostoc, Anabaena). Mushrooms such as Agaricus are grown as food, and Spirogyra is an ordinary green alga.
📘 Read it in NCERT: Class 12 Biology, Ch 8 (practise this chapter) · Class 12 Biology, Ch 8 (practise this chapter) · Class 9 Exploration, Ch 12 (practise this chapter)
Sources
- NCERT Class 12 · Biology, Chapter 8 “In paddy fields, cyanobacteria serve as an important biofertiliser.”
- NCERT Class 12 · Biology, Chapter 8 “Cyanobacteria are autotrophic microbes widely distributed in aquatic and terrestrial environments many of which can fix atmospheric nitrogen, e.g. Anabaena, Nostoc, Oscillatoria, etc.”
- National Horticulture Board, Button Mushroom ↗ “The species being grown in most farms is the white button mushroom ( Agaricus bisporus ) belonging to Class Basidiomycetes and Family Agaricaceae.”
- NCERT Class 9 · Exploration, Chapter 12 “An example of Thallophyta is Spirogyra (Fig. 12.9).”
Question: UPSC Civil Services (Preliminary) 2013, General Studies paper. Explanation: Minimalist IAS, checked 25 Oct 2026 (how we verify). ·