Q30. Mycorrhiza is an example of which ecological interaction?
[UP Junior Aided Teacher, 2021]
(a) Fungistasis
(b) Mutualism
(c) Amensalism
(d) Antibiosis
Answer: (b) Mutualism
Explanation: In a mycorrhizal relationship, the fungus receives carbohydrates made by the host plant while helping roots absorb phosphorus, water and other nutrients. Because both partners benefit under typical conditions, this interaction is classified as mutualism rather than antibiosis or amensalism.
Q29. Which biofertilizer is added to rice fields?
[MPSC Subordinate Services Prelims 2020, held 4 September 2021]
(a) Red algae
(b) Brown algae
(c) Rhizobium
(d) Blue-green algae
Answer: (d) Blue-green algae
Explanation: Nitrogen-fixing blue-green algae, or cyanobacteria, thrive in flooded rice fields and enrich them with biologically fixed nitrogen. Common examples include Nostoc and Anabaena. Rhizobium instead forms symbiotic nodules primarily on leguminous plants and is not the standard answer here.
Q28. Azotobacter is a/an ________.
[SSC JE Civil, 29 October 2020, morning]
(a) Nitrogen-fixing bacterium
(b) Antibiotic
(c) Sulphur-fixing bacterium
(d) Virus
Answer: (a) Nitrogen-fixing bacterium
Explanation: Azotobacter is a genus of free-living nitrogen-fixing bacteria common in soil. Its capacity to reduce atmospheric nitrogen helps improve fertility and supports plant growth. It is neither a virus nor an antibiotic, and its principal agricultural role concerns nitrogen rather than sulphur fixation.
Q27. Which is NOT a nitrogen-fixing biofertilizer?
[SSC JE Civil, 30 October 2020, evening]
(a) Azotobacter
(b) Rhizobium
(c) Pseudomonas
(d) Azolla
Answer: (c) Pseudomonas
Explanation: In the classification used for this question, Pseudomonas is not grouped with conventional nitrogen-fixing inoculants. Many Pseudomonas strains instead solubilize phosphorus or support plant growth. Azotobacter, Rhizobium and the Azolla–cyanobacterium partnership are familiar nitrogen-fixing systems.
Q26. Which nitrogen-fixing actinomycete forms associations with higher plants?
[UGC NET Environmental Science, 29 September 2020, Shift 2]
(a) Azospirillum
(b) Clostridium
(c) Frankia
(d) Anabaena
Answer: (c) Frankia
Explanation: Frankia is a filamentous actinobacterium that forms nitrogen-fixing nodules in actinorhizal plants such as Alnus and Casuarina. Unlike typical Rhizobium–legume partnerships, Frankia associates with several non-leguminous woody plants and supplies biologically fixed nitrogen to these hosts.
Q25. Match the biofertilizers to crops:
(a) Rhizobium,
(b) Azospirillum,
(c) Acetobacter,
(d) Azolla;
(i) non-legume crops,
(ii) sugarcane,
(iii) legume crops,
(iv) lowland paddy.
[MPSC State Services Mains 2020, General Studies IV]
(a) (a)–(iii), (b)–(ii), (c)–(iv), (d)–(i)
(b) (a)–(iii), (b)–(ii), (c)–(i), (d)–(iv)
(c) (a)–(i), (b)–(iii), (c)–(iv), (d)–(ii)
(d) (a)–(iii), (b)–(i), (c)–(ii), (d)–(iv)
Answer: (d) (a)–(iii), (b)–(i), (c)–(ii), (d)–(iv)
Explanation: Rhizobium is used with legumes; Azospirillum is associated with roots of non-legume crops; Gluconacetobacter diazotrophicus is notable in sugarcane; and Azolla supports nitrogen nutrition in flooded rice cultivation. This is the correspondence specified in the MPSC paper.
Q24. Which of the following is used as a biofertilizer?
[CGPSC Civil Services Prelims, 2019]
(a) Rhizobium
(b) Blue-green algae
(c) Azolla
(d) All of these
Answer: (d) All of these
Explanation: Rhizobium fixes nitrogen in legume nodules, nitrogen-fixing cyanobacteria enrich soil, and Azolla houses cyanobacteria capable of nitrogen fixation. All three are used in biofertilization, although they differ in biology and farming applications. Therefore the inclusive choice is correct.
Q23. Nitrogen-fixing bacteria form a close association with root cells of which crops?
[UPPSC PCS Prelims, 2019]
(a) Pulses
(b) Rice
(c) Wheat
(d) Sugarcane
Answer: (a) Pulses
Explanation: Pulse crops are legumes and commonly form root nodules containing rhizobia. These bacteria fix atmospheric nitrogen and share the fixed compounds with the host, while receiving plant-derived carbon. Rice, wheat and sugarcane generally do not form this conventional Rhizobium–legume nodule symbiosis.
Q22. Which group is associated with biological nitrogen fixation?
[UPPSC PCS Prelims, 2019]
(a) Red algae
(b) Brown algae
(c) Green algae
(d) Blue-green algae
Answer: (d) Blue-green algae
Explanation: Certain blue-green algae, now classified as cyanobacteria, fix nitrogen using nitrogenase. Nostoc and Anabaena are familiar examples. Their biological nitrogen inputs are particularly valuable in submerged paddy soils and are a foundation of cyanobacterial biofertilizer technology.
Q21. Which of the following is a phosphatic biofertilizer?
[UPPSC Block Education Officer Prelims, 2019]
(a) Rhizobium
(b) Blue-green algae
(c) Azolla
(d) Vesicular-arbuscular mycorrhiza
Answer: (d) Vesicular-arbuscular mycorrhiza
Explanation: Vesicular-arbuscular mycorrhizal fungi, now usually called arbuscular mycorrhizal fungi, extend hyphae beyond the root depletion zone. They increase uptake of poorly mobile phosphorus and can improve water acquisition. The other options are associated primarily with nitrogen fixation.
