Question
Among the following pairs of microbes, which pair has both the microbes that can be used as biofertilisers? [NEET (Odisha) 2019]
(a) Aspergillus and Rhizopus
(b) Rhizobium and Rhizopus
(c) Cyanobacteria and Rhizobium
(d) Aspergillus and Cyanobacteria
Answer/Explanation
Ans. (c)
Biofertilisers are organisms that enrich the nutrient quality of the soil. For example, Cyanobacteria and Rhizobium. Aspergillus and Rhizopus are not used as biofertilisers.
Question
Which one of the following microbes forms symbiotic association with plants and helps them in their nutrition? [CBSE AIPMT 2012, 11]
(a) Azotobacter
(b) Aspergillus
(c) Glomus
(d) Trichoderma
Answer/Explanation
Ans. (c)
Several species of Glomus, including G. aggregatum, are cultured and sold as mycorrhizal inoculant for agricultrural soils. Being endomycorrhiza, it helps the plants in the absorption of nutrients especially phosphorus from soil.
Question
A nitrogen-fixing microbe associated with Azolla in rice fields is [CBSE AIPMT 2012]
(a) Spirulina
(b) Anabaena
(c) Frankia
(d) Tolypothrix
Answer/Explanation
Ans. (b)
Anabaena azollae is a free-living nitrogen fixing blue-green alga or cyanobacterium but it may also live symbiotically in the leaf cavities of Azolla, an aquatic, free floating, freshwater pteridophyte (fern). This cyanobacterium has nitrogenase enzyme, therefore can fix nitrogen. If this fern is grown in paddy (rice) fields, a remarkable $50 \%$ increase in yield can be noticed.
Question
An organism used as a biofertiliser for raising soyabean crop is [CBSE AIPMT 2011]
(a) Azospirillum
(b) Rhizobium
(c) Nostoc
(d) Azotobacter
Answer/Explanation
Ans. (b)
Rhizobium leguminosarum is a symbiotic bacteria found in root nodules of legume. This bacterium has nitrogen fixing nif gene. Soyabean is a legume. Thus, Rhizobium is used as a biofertiliser for raising soyabean crop.
Question
Which one of the following is not a biofertiliser? [CBSE AIPMT 2011]
(a) Rhizobium
(b) Nostoc
(c) Mycorrhiza
(d) Agrobacterium
Answer/Explanation
Ans. (d)
Out of the following only Agrobacterium is not a biofertiliser. It is a Gram-negative bacterium that causes tumours in plants. It is well known for its ability to transfer DNA between itself and plants, and for this reason it has become an important tool for genetic engineering.
A tumefaciens causes crown-gall disease in plants. It has Ti-plasmid.
Question
The free-living, anaerobic nitrogen-fixer is [CBSE AIPMT 2010]
(a) Beijerinckia
(b) Rhodospirillum
(c) Rhizobium
(d) Azotobacter
Answer/Explanation
Ans. (b)
Rhodospirillum is a free-living, anaerobic, nitrogen fixer. Both Beijerinckia and Azotobacter are free-living, nitrogen-fixing, aerobic microbes. Rhizobium is a symbiotic, nitrogen fixer.
Question
The common nitrogen-fixer in paddy fields is [CBSE AIPMT 2010]
(a) Rhizobium
(b) Azospirillum
(c) Oscillatoria
(d) Frankia
Answer/Explanation
Ans. (b)
Azospirillum is a nitrogen fixing bacterium in paddy fields. It is very useful soil and root bacterium. It is an associative symbiotic $\mathrm{N}_2$-fixing bacteria. When it is added to the soil, it multiplies in millions and can supply $20-40 \mathrm{~kg}$ of nitrogen per hectare per season.
Question
Which one of the following is not used in organic farming? [CBSE AIPMT 2010]
(a) Oscillatoria
(b) Snail
(c) Glomus
(d) Earthworm
Answer/Explanation
Ans. (b)
Except snail, all these are used in organic farming-
Glomus – Endomycorrhiza
Oscillatoria – BGA
Earthworm – Vermicompost
Question
Which one the following statements is correct? [CBSE AIPMT 2007]
(a) Extensive use of chemical fertilisers may lead to eutrophication of nearby water bodies
(b) Both Azotobacter and Rhizobium fix atmospheric nitrogen in root nodules of plants
(c) Cyanobacteria such as Anabaena and Nostoc are important mobilisers of phosphates and potassium for plant nutrition in soil
(d) At present it is not possible to grow maize without chemical fertilisers
Answer/Explanation
Ans. (a)
Out of the following statement (a) is correct as eutrophication is caused by run off water from fertilised fields, sub-urban lawns, feed lots and detergent rich sewage. It is phenomenon of nutrient enrichment of a water body.
Question
A free-living nitrogen-fixing cyanobacterium which can also form symbiotic association with the water fern Azolla is [CBSE AIPMT 2004]
(a) Tolypothrix
(b) Chlorella
(c) Nostoc
(d) Anabaena
Answer/Explanation
Ans. (d)
Anabaena is a free-living nitrogen fixing cyanobacterium which can form symbiotic association with water fern Azolla.
Question
Which of the following plants are used as green manure in crop fields and in sandy soils? [CBSE AIPMT 2003]
(a) Saccharum munja and Lantana camara
(b) Dichanthium annulatum and Azolla
(c) Crotalaria juncea and Alhagi comelorum
(d) Calotropis procera and Phyllanthus niruri
Answer/Explanation
Ans. (c)
Crotalaria juncea(sunnhemp) and Alhagi camelorum are among the plants which are used as green manures in India. These green manures help the soil through increasement of area, water holding capacities and fertility.
Question
The aquatic fern, which is an excellent biofertiliser is [CBSE AIPMT 2001, 1999]
(a) Azolla
(b) Pteridium
(c) Salvinia
(d) Marselia
Answer/Explanation
Ans. (a)
Azolla leaves harbour Anabaena colonies which fix atmospheric nitrogen. The nitrogen rich Azolla is used as biofertiliser.
Question
Farmers have reported over $50 \%$ higher yields of rice by sing which of the following biofertiliser? [CBSE AIPMT 2000, 99, 98]
(a) Mycorrhiza
(b) Azolla pinnata
(c) Cyanobacteria
(d) Legume-Rhizobium symbiosis
Answer/Explanation
Ans. (b)
Anabaena azollae, a cyanobacterium living in the cavities of fern Azolla, fixes atmospheric nitrogen and releases it into the leaf cavity of the fern. Farmers have reported over $50 \%$ higher yields by using Azolla pinnata.
Question
Which of the following is non-symbiotic biofertiliser? [CBSE AIPMT 1998]
(a) VAM
(b) Azotobacter
(c) Anabaena
(d) Rhizobium
Answer/Explanation
Ans. (b)
Free-living (non-symbiotic) bacteria like Azotobacter and Bacillus polymyxa fix atmospheric nitrogen and make it available to crop plants. VAM (Vasicular Arbuscular Mycorrhizae) is an endosymbiosis between fungi and roots of higher plants.
Anabaena is a cyanobacterium (blue-green algae) which live solitary or in association with other plant and can fix atmospheric $\mathrm{N}_2$.
Rhizobium bacterium makes symbiotic association with leguminous plants.