UPSC CSE Prelims
Question 20
Consider the following organisms:
- Agaricus
- Nostoc
- Spirogyra
Which of the above is/are used as biofertilizer/biofertilizers?
View correct answer and explanation
Correct answer: B
Correct Option: B
Explanation: Nostoc, a nitrogen-fixing cyanobacterium, is used to enrich agricultural soils; Agaricus is a mushroom and Spirogyra is green algae.
Statement/Pair-wise Analysis:
Statement/Item 1: Incorrect - Agaricus is a basidiomycete mushroom, not the usual nitrogen-fixing biofertilizer.
Statement/Item 2: Correct - Nostoc fixes atmospheric nitrogen and is used as a biofertilizer, including in paddy cultivation.
Statement/Item 3: Incorrect - Spirogyra is a freshwater filamentous green alga, not a standard nitrogen-fixing inoculant.
Option-wise Analysis:
A: Incorrect - includes false item 1.
B: Correct - selects all and only the accurate statements/pairs.
C: Incorrect - includes false item 3.
D: Incorrect - includes false item 3 and excludes true item 2.