Part 6: Microbes as Biofertilizers (25 MCQs)
Part 6: Microbes as Biofertilizers – Nitrogen-fixers, Mycorrhiza, Cyanobacteria, Applications in agriculture (25 MCQs)
Q126. Biofertilizers are:
a) Synthetic fertilizers
b) Living organisms that enhance nutrient availability to plants
c) Hormones applied to crops
d) Pesticides used in farming
Answer: b
- b) Correct: Biofertilizers = microbes that improve soil fertility & nutrient supply.
Q127. Rhizobium forms symbiotic association with:
a) Rice roots
b) Leguminous plant roots
c) Maize roots
d) Wheat roots
Answer: b
- b) Correct: Rhizobium forms root nodules in legumes → nitrogen fixation.
Q128. Which enzyme fixes atmospheric nitrogen?
a) Rubisco
b) Nitrogenase
c) Nitrate reductase
d) Dehydrogenase
Answer: b
- b) Correct: Nitrogenase enzyme → biological nitrogen fixation.
Q129. Free-living nitrogen-fixer in soil is:
a) Rhizobium
b) Azotobacter
c) Nostoc
d) Both b and c
Answer: d
- d) Correct: Azotobacter (soil) and Nostoc (cyanobacteria) fix N₂.
Q130. Anabaena and Nostoc are:
a) Fungi
b) Cyanobacteria
c) Algae
d) Actinomycetes
Answer: b
- b) Correct: Anabaena & Nostoc → cyanobacteria fixing nitrogen.
Q131. Cyanobacteria are important biofertilizers for:
a) Rice paddies
b) Wheat fields
c) Sugarcane farms
d) Cotton fields
Answer: a
- a) Correct: Blue-green algae (BGA) like Anabaena fix N₂ in paddy fields.
Q132. Azolla-Anabaena symbiosis is useful in:
a) Rice cultivation
b) Maize cultivation
c) Potato farming
d) Mango orchards
Answer: a
- a) Correct: Azolla (fern) + Anabaena → natural biofertilizer in rice.
Q133. Frankia forms nitrogen-fixing nodules in:
a) Legumes
b) Alnus (non-legume trees)
c) Rice
d) Wheat
Answer: b
- b) Correct: Frankia (actinobacteria) → symbiosis with Alnus.
Q134. Mycorrhiza is an association between:
a) Fungus and algae
b) Fungus and plant roots
c) Bacteria and fungi
d) Cyanobacteria and fungi
Answer: b
- b) Correct: Mycorrhiza = fungus + plant root symbiosis.
Q135. Benefits of mycorrhiza include:
a) Absorption of phosphorus
b) Tolerance to salinity & drought
c) Resistance to pathogens
d) All of the above
Answer: d
- d) Correct: Mycorrhiza provide multiple benefits.
Q136. Which mycorrhizal fungus is used as biofertilizer?
a) Glomus
b) Aspergillus
c) Penicillium
d) Trichoderma
Answer: a
- a) Correct: Glomus → arbuscular mycorrhiza in plant roots.
Q137. Which of the following increases phosphorus uptake in plants?
a) Rhizobium
b) Mycorrhizal fungi
c) Azotobacter
d) Anabaena
Answer: b
- b) Correct: Mycorrhiza → better absorption of phosphorus.
Q138. Phosphate-solubilizing bacteria include:
a) Bacillus and Pseudomonas
b) Rhizobium and Azolla
c) Aspergillus and Saccharomyces
d) Methanogens
Answer: a
- a) Correct: Bacillus, Pseudomonas → release phosphorus from insoluble forms.
Q139. The main benefit of biofertilizers is:
a) Increase crop yield sustainably
b) Reduce use of chemical fertilizers
c) Improve soil health
d) All of the above
Answer: d
- d) Correct: Biofertilizers = sustainable, eco-friendly soil enrichment.
Q140. Which is NOT a biofertilizer?
a) Azotobacter
b) Rhizobium
c) Nostoc
d) Streptococcus
Answer: d
- d) Correct: Streptococcus = human pathogen, not a biofertilizer.
Q141. Which biofertilizer is used in non-legume crops?
a) Rhizobium
b) Azotobacter
c) Frankia
d) Lactobacillus
Answer: b
- b) Correct: Azotobacter free-living → fixes N₂ in non-legumes.
Q142. Which cyanobacterium lives in symbiosis with Azolla?
a) Nostoc
b) Anabaena
c) Oscillatoria
d) Rivularia
Answer: b
- b) Correct: Azolla + Anabaena → symbiotic nitrogen fixation.
Q143. The root nodules of legumes turn pink due to:
a) Hemoglobin
b) Leghemoglobin
c) Myoglobin
d) Chlorophyll
Answer: b
- b) Correct: Leghemoglobin regulates O₂ for nitrogenase enzyme.
Q144. Symbiotic nitrogen-fixers in legumes include:
a) Azotobacter
b) Rhizobium
c) Frankia
d) Both b and c
Answer: b
- b) Correct: Rhizobium in legumes. Frankia = non-legume symbiont.
Q145. Which biofertilizer improves soil fertility in paddy fields?
a) Anabaena
b) Nostoc
c) Azolla
d) All of the above
Answer: d
- d) Correct: All three → enrich rice fields with nitrogen.
Q146. Which biofertilizer is also used in deserts for sand dune stabilization?
a) Nostoc (cyanobacteria)
b) Rhizobium
c) Azotobacter
d) Frankia
Answer: a
- a) Correct: Nostoc fixes nitrogen & stabilizes soil in deserts.
Q147. Mycorrhiza helps plants in nutrient uptake especially in:
a) Potassium
b) Phosphorus
c) Nitrogen
d) Calcium
Answer: b
- b) Correct: Mycorrhiza enhance phosphorus absorption.
Q148. A biofertilizer useful for maize and sugarcane is:
a) Azospirillum
b) Rhizobium
c) Frankia
d) Lactobacillus
Answer: a
- a) Correct: Azospirillum → associative symbiosis in cereals like maize.
Q149. Biofertilizers are preferred over chemical fertilizers because they:
a) Are cheaper
b) Are eco-friendly
c) Improve soil fertility long-term
d) All of the above
Answer: d
- d) Correct: Biofertilizers = sustainable + eco-friendly + cost-effective.
Q150. Which of the following is incorrectly matched?
a) Rhizobium – legumes
b) Azotobacter – free-living nitrogen fixer
c) Frankia – cereals
d) Nostoc – cyanobacteria
Answer: c
- c) Correct: Frankia = non-legume trees (Alnus), not cereals.
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