Q10. Which of the following microorganisms are used as biofertilizers?
[UPPSC PCS Mains, 2012]
(a) Virus
(b) Cyanobacteria
(c) Protozoa
(d) None of the above
Answer: (b) Cyanobacteria
Explanation: Nitrogen-fixing cyanobacteria such as Nostoc and Anabaena are commonly used to enrich rice-growing soils. Although certain beneficial fungi also serve as biofertilizers, the examination identifies cyanobacteria as the specific expected category among the listed choices.
Q9. Azolla is often used as a biofertilizer because it is associated with which organism?
[UPPSC PCS Mains, 2011]
(a) Fungus
(b) Blue-green algae
(c) Red algae
(d) Moss
Answer: (b) Blue-green algae
Explanation: Azolla hosts nitrogen-fixing cyanobacteria traditionally called blue-green algae. The symbiont supplies usable nitrogen, while the fern supplies housing and nutrients. This partnership explains why Azolla biomass is incorporated into submerged rice paddies as a biological nitrogen source.
Q8. Blue-green algae are used to supply nitrogen to which crop?
[UPPSC PCS Mains, 2010]
(a) Paddy
(b) Bajra
(c) Maize
(d) Wheat
Answer: (a) Paddy
Explanation: Cyanobacteria flourish in many flooded rice fields, where nitrogen-fixing species can convert atmospheric nitrogen into usable nitrogen compounds. This contribution supports paddy cultivation. Dryland cereals do not normally offer the same continuously flooded environment needed for typical paddy inoculation.
Q7. Which of the following is a source of biofertilizer?
[UPPSC PCS Mains, 2009]
(a) Yeast
(b) Chlorella
(c) Azolla
(d) Mould
Answer: (c) Azolla
Explanation: Azolla is a nitrogen-enriching aquatic fern that contains nitrogen-fixing cyanobacteria. It is widely recognized for its use as a biofertilizer in wetland rice systems. The other listed organisms are not the conventional biofertilizer source intended by this question.
Q6. Azolla provides a useful biofertilizer when associated with which of the following?
[Uttarakhand PCS Prelims, 2007]
(a) Blue-green algae
(b) Bone meal
(c) Cow dung
(d) Urea
Answer: (a) Blue-green algae
Explanation: Azolla harbours blue-green algae, especially the Anabaena-associated nitrogen-fixing symbiont, in leaf cavities. This partnership adds biologically fixed nitrogen to the aquatic fern and ultimately to cultivated soil. Bone meal, dung and urea do not describe this symbiotic partner.
Q5. Blue-green algae are chiefly used as biofertilizers for which crop?
[UPPSC PCS Prelims, 2006]
(a) Wheat
(b) Gram
(c) Paddy
(d) Mustard
Answer: (c) Paddy
Explanation: Certain cyanobacteria such as Nostoc and Anabaena fix atmospheric nitrogen and thrive in the flooded conditions of paddy farming. They help improve nitrogen availability and can reduce the requirement for mineral nitrogen fertilizers. Thus rice is their classic agricultural application.
Q4. Which bacterium is associated with nitrogen fixation in soybean?
[UPPSC PCS Prelims, 2006]
(a) Rhizobium leguminosarum
(b) Rhizobium japonicum
(c) Rhizobium phaseoli
(d) Rhizobium trifolii
Answer: (b) Rhizobium japonicum
Explanation: Rhizobium japonicum is the older taxonomic name for the soybean-associated nitrogen fixer now generally classified as Bradyrhizobium japonicum. In root nodules, the symbiont converts atmospheric nitrogen to compounds supporting soybean growth. The other names are linked with different legume hosts.
Q3. Where is leghemoglobin found?
[UPPSC PCS Mains, 2005]
(a) Human blood
(b) Rabbit blood
(c) Root nodules of legumes
(d) Chicken blood
Answer: (c) Root nodules of legumes
Explanation: Leghemoglobin is an oxygen-binding heme protein located in active root nodules of legumes. Its red pigment buffers oxygen so that bacteria can respire while the nitrogenase enzyme remains protected. It is distinct from the haemoglobin circulating in animal blood.
Q2. Which of the following pairs is incorrectly matched?
[UP Lower Subordinate Special Prelims, 2003]
(a) Blue-green algae — biofertilizer
(b) Chrysopa — biological control of aphids
(c) BIO 902 — mustard variety
(d) Azotobacter — bioinsecticide
Answer: (d) Azotobacter — bioinsecticide
Explanation: Azotobacter is a free-living nitrogen-fixing bacterium used as a biofertilizer, not a bioinsecticide. Chrysopa lacewing larvae prey on insect pests, while nitrogen-fixing blue-green algae improve soil fertility. The distinction separates nutrient-enriching inoculants from pest-control agents.
Q1. Which of the following is a biofertilizer?
[Uttarakhand PCS Mains, 2002]
(a) Urea
(b) 2,4-D
(c) Streptocycline
(d) Azolla
Answer: (d) Azolla
Explanation: Azolla is an aquatic fern associated with nitrogen-fixing cyanobacteria and used to enrich rice-growing soils. Urea is a mineral nitrogen fertilizer, 2,4-D is a herbicide, and streptocycline is an antibiotic preparation. Only Azolla functions as the specified biofertilizer.
