Biofertilizer Questions in English

(B) Non-symbiotic biofertilizers are free-living microorganisms that fix atmospheric nitrogen independently without forming a symbiotic association with plants.
$Azotobacter$ is a well-known free-living (non-symbiotic) nitrogen-fixing bacterium.
$VAM$ (Vesicular-Arbuscular Mycorrhiza) is a symbiotic association between fungi and plant roots.
$Rhizobium$ is a symbiotic nitrogen-fixing bacterium found in the root nodules of legumes.
$Anabaena$ can be free-living but is most commonly associated with the water fern $Azolla$ in a symbiotic relationship.
Therefore,$Azotobacter$ is the correct answer.

(D) Biofertilizers are organisms that enrich the nutrient quality of the soil.
$1$. Nitrogen-fixing bacteria (e.g.,$Rhizobium$,$Azospirillum$) fix atmospheric nitrogen into the soil.
$2$. Nitrogen-fixing cyanobacteria (e.g.,$Anabaena$,$Nostoc$) also add nitrogen to the soil,especially in paddy fields.
$3$. Mycorrhiza (fungal association with roots of higher plants) helps in the absorption of phosphorus from the soil.
Therefore,all the listed options are examples of biofertilizers.

(C) $Nostoc$ is a genus of cyanobacteria that is capable of fixing atmospheric nitrogen $(N_2)$ into ammonia,which plants can utilize for growth. Due to this nitrogen-fixing ability,it is used as a biofertilizer and is often referred to as green manure in agricultural practices.

(A) $Anabaena$ is a genus of filamentous cyanobacteria that exists as plankton. It is known for its ability to fix atmospheric nitrogen into ammonia,which can be utilized by plants. Due to this nitrogen-fixing capability,it is widely used in agriculture,particularly in paddy fields,as a biofertilizer to enhance soil fertility and crop yield.

(B) $Azolla pinnata$ is a small aquatic fern that has a symbiotic relationship with the nitrogen-fixing cyanobacterium $Anabaena azollae$.
When used as a biofertilizer in rice fields,it provides a significant amount of nitrogen to the soil.
Farmers have reported that the application of $Azolla$ can increase rice yields by over $50\%$ due to its nitrogen-fixing capabilities and its role as a green manure.

(A) $Nostoc$ contains specialized cells known as heterocysts,which are responsible for the fixation of atmospheric nitrogen $(N_2)$.
Due to this ability to enrich the soil with nitrogen,$Nostoc$ is widely used as a biofertilizer.

(B) Biofertilizers are organisms that enrich the nutrient quality of the soil.
$A$. $Rhizobium$ forms a symbiotic association with leguminous roots to fix atmospheric nitrogen.
$B$. Algae and fungi (Lichens) are symbiotic associations,but they are not used as biofertilizers in agriculture.
$C$. $Azolla$ (a water fern) and $Anabaena$ (a cyanobacterium) form a symbiotic association that fixes nitrogen,commonly used in rice fields.
$D$. Roots of higher plants and fungi form mycorrhizae,which help in phosphorus absorption and are considered biofertilizers.
Therefore,the correct answer is $B$.

(A) $Azolla$ is an aquatic fern that lives in a symbiotic relationship with the nitrogen-fixing cyanobacterium $Anabaena$ $azollae$.
This association allows $Azolla$ to fix atmospheric nitrogen,making it an excellent biofertilizer,particularly in rice paddies.

(C) $Azolla$ is used as a biofertilizer because it contains a symbiotic association with nitrogen-fixing cyanobacteria, specifically $Anabaena \, azollae$, in its leaf cavities.
These cyanobacteria are capable of fixing atmospheric nitrogen, which enriches the soil with nitrogenous nutrients, making $Azolla$ highly beneficial for crops like rice.

(B) Fertilizers are substances added to soil to provide essential nutrients for plant growth.
$Urea$ $(NH_2CONH_2)$ is a widely used nitrogenous fertilizer that provides nitrogen,an essential macronutrient for plants.
Ammonium chloride is a salt,calcium citrate is a food additive,and calcium carbonate is a mineral/liming agent,not a primary fertilizer.

(C) The fertility of the soil in rice fields is significantly improved by the use of biofertilizers like $Blue-green$ $algae$ (cyanobacteria).
Specifically,species such as $Aulosira$ $fertilissima$ are known to be excellent nitrogen fixers in waterlogged rice fields.
These organisms fix atmospheric nitrogen into ammonia,which increases the nitrogen content of the soil and promotes plant growth.
$Rhizobium$ is typically associated with leguminous plants,not rice.

(D) Paddy fields (rice cultivation) require significant amounts of nitrogen for optimal growth. Cyanobacteria,such as $Anabaena$ and $Nostoc$,are commonly found in paddy fields. These organisms can fix atmospheric nitrogen,either symbiotically (e.g.,$Anabaena$ $azollae$ in $Azolla$ ferns) or non-symbiotically (free-living),thereby enriching the soil with nitrogen and acting as an excellent biofertilizer for rice crops.

(B) $Rhizobium$ bacteria live symbiotically in the root nodules of leguminous plants.
These bacteria fix atmospheric nitrogen $(N_2)$ into organic forms,which the plants can utilize for growth.
This symbiotic association increases the soil fertility,making $Rhizobium$ an important biofertilizer.

(C) $VAM$ stands for Vesicular Arbuscular Mycorrhiza.
These are a type of endomycorrhizal fungi where the fungal hyphae penetrate the cortical cells of the plant roots.
Inside the cells,these hyphae form specialized structures known as vesicles (for storage) or arbuscules (for nutrient exchange).
Therefore,$VAM$ is classified as an endomycorrhiza.

(D) Biofertilizers are organisms that enrich the nutrient quality of the soil. They are primarily of three types:
$1$. Nitrogen-fixing bacteria: Examples include $Rhizobium$,$Azospirillum$,and $Azotobacter$.
$2$. Nitrogen-fixing cyanobacteria: Examples include $Anabaena$,$Nostoc$,and $Oscillatoria$.
$3$. Mycorrhizal fungi: These fungi form symbiotic associations with plant roots,such as the genus $Glomus$,which absorbs phosphorus from the soil.
Therefore,the correct option is $D$.

(A) Azolla is a small aquatic fern that has a symbiotic relationship with the nitrogen-fixing cyanobacterium $Anabaena$ $azollae$.
This cyanobacterium resides in the leaf cavities of $Azolla$.
It fixes atmospheric nitrogen into ammonia,which is then utilized by the rice plants,thereby enriching the soil with nitrogen.

(A) $Azolla$ $pinnata$ is a small aquatic fern that has a symbiotic relationship with the nitrogen-fixing cyanobacterium $Anabaena$ $azollae$.
This association allows $Azolla$ to fix atmospheric nitrogen,which is then released into the water and soil upon the decomposition of the fern.
Because paddy crops require flooded conditions,$Azolla$ grows abundantly in these fields,making it an excellent natural biofertilizer that significantly increases rice yield.

(D) Biofertilizers are organisms that enrich the nutrient quality of the soil.
$1$. Cow dung manure and farmyard waste are organic fertilizers that provide essential nutrients to the soil.
$2$. Green manure involves growing quick-growing crops and ploughing them back into the soil to increase fertility.
$3$. $BGA$ (Blue-Green Algae) like Anabaena and the fern Azolla are well-known biofertilizers that fix atmospheric nitrogen,thereby enhancing soil fertility.
Since all these options contribute to improving soil nutrient status,the correct answer is $D$.

(B) $Nostoc$ and $Anabaena$ are free-living nitrogen-fixing cyanobacteria.
They increase the nitrogen content of moist soil and water bodies.
This enrichment of nitrogen acts as a natural fertilizer,which significantly increases the yield of paddy crops.

(A) $Azolla$ $pinnata$ is an aquatic fern that has a symbiotic association with the nitrogen-fixing cyanobacterium $Anabaena$ $azollae$.
This association helps in fixing atmospheric nitrogen,which significantly enriches the soil with nutrients.
When used as a biofertilizer in rice fields,it provides a continuous supply of nitrogen to the crop,leading to a substantial increase in yield,often reported up to $50\%$ higher compared to fields without such biofertilizers.

(B) $Azolla$ $pinnata$ (an aquatic fern) contains symbiotic nitrogen-fixing cyanobacteria ($Anabaena$ $azollae$) in its leaf cavities.
It is widely used as a biofertilizer in rice fields,particularly in south-eastern Asia.
It helps in nitrogen fixation and has been found to increase crop yield by up to $50\%$.

(C) Biofertilizers are organisms that enrich the nutrient quality of the soil. They include bacteria,fungi,and cyanobacteria. They fix atmospheric nitrogen,solubilize phosphorus,or decompose organic matter,thereby maintaining or increasing the soil fertility. Therefore,the correct option is $C$.

(A) $Azolla$ is a small aquatic fern that maintains a symbiotic relationship with the nitrogen-fixing cyanobacterium $Anabaena$ $\text{azollae}$.
This cyanobacterium resides in the cavities of the $Azolla$ leaves.
It fixes atmospheric nitrogen, which is then utilized by the fern for its growth, making $Azolla$ an excellent biofertilizer in rice fields.

(A) $VAM$ stands for Vesicular-Arbuscular Mycorrhiza.
It is a type of symbiotic association between fungi and plant roots.
These fungi help in the absorption of nutrients,especially phosphorus,from the soil,thereby acting as a biofertilizer.
Sporeine and Devine are bioherbicides,and Agent Orange is a chemical herbicide.

(B) Azolla is a small aquatic fern that has a symbiotic relationship with the cyanobacterium $Anabaena \text{ } azollae$. This cyanobacterium resides in the leaf cavities of Azolla and fixes atmospheric nitrogen, which makes Azolla an excellent biofertilizer for rice fields.

(D) Blue-green algae (cyanobacteria) such as $Anabaena$ and $Nostoc$ are used as biofertilizers.
These organisms possess specialized cells called heterocysts that are capable of fixing atmospheric nitrogen into ammonia,which enriches the soil with nitrogenous nutrients.
Therefore,their ability to fix nitrogen makes them effective biofertilizers.

(A) Green manure is obtained by growing,green-manuring or mulching with green crop parts. These are young leguminous crops like $Sesbania$ $aculeata$,$Sesbania$ $rostrata$,and $Crotalaria$ $juncea$,which are ploughed back into the soil to enrich it with nitrogen and organic matter. Therefore,$Sesbania$ is a green manure.

(A) Anabaena is a genus of filamentous cyanobacteria that exists as plankton. It is known for its nitrogen-fixing abilities. In paddy fields (rice fields),Anabaena azollae (a species of Anabaena) lives in symbiotic association with the water fern Azolla. This association helps in fixing atmospheric nitrogen,which acts as a biofertilizer,thereby significantly increasing the yield of rice crops.

(A) $Guano$ is the excrement of sea birds,bats,and seals.
It is found in large quantities along the coast of Chile and Peru.
It is highly rich in phosphorus and nitrogen,making it an excellent natural fertilizer.
Therefore,the correct option is $A$.

(D) $Azolla$ is a small aquatic fern that has a symbiotic relationship with the nitrogen-fixing cyanobacterium $Anabaena$ $azollae$. This cyanobacterium lives in the cavities of the $Azolla$ leaves. Because of this association,$Azolla$ is widely used as a biofertilizer in paddy fields. It fixes atmospheric nitrogen,which enhances the growth of rice plants and significantly increases the crop yield.

(D) Paddy fields (rice fields) provide an ideal environment for the growth of nitrogen-fixing cyanobacteria.
$Anabaena$ and $Nostoc$ are the most common nitrogen fixers associated with the water fern $Azolla$ in paddy fields.
Among the given options,$Oscillatoria$ is a cyanobacterium capable of nitrogen fixation,which is commonly found in such aquatic environments.
$Rhizobium$ is typically associated with the root nodules of leguminous plants,while $Azospirillum$ is often associated with the roots of grasses.
Therefore,$Oscillatoria$ is the most appropriate answer among the choices provided.

(B) $Azolla\, pinnata$ is a small aquatic fern that lives in a symbiotic relationship with the nitrogen-fixing cyanobacterium $Anabaena\, azollae$.
Due to this association,it is widely used as a biofertilizer in rice fields to increase nitrogen content in the soil,thereby enhancing crop yield.

(D) $Azolla$ is a small aquatic fern that has a symbiotic relationship with the cyanobacterium $Anabaena$ $azollae$.
This cyanobacterium lives in the cavities of the $Azolla$ leaves and fixes atmospheric nitrogen,which is then utilized by the rice plants in flooded fields.
Therefore,$Anabaena$ is the correct microorganism associated with $Azolla$ for nitrogen fixation.

(C) The correct answer is $C$. $Azolla$ $pinnata$ is a small aquatic fern that has a symbiotic relationship with the nitrogen-fixing cyanobacterium $Anabaena$ $azollae$. This association allows the fern to fix atmospheric nitrogen,which significantly enriches the soil. When used as a biofertilizer in paddy (rice) fields,it can increase the crop yield by more than $50\%$ due to the enhanced nitrogen availability.

(D) $Azolla$ is a small aquatic fern that has a symbiotic relationship with the nitrogen-fixing cyanobacterium $Anabaena$ $azollae$.
Because of this association,$Azolla$ is widely used as a biofertilizer in rice fields.
It helps in fixing atmospheric nitrogen,which enhances the growth and yield of the rice crop.
Therefore,$Azolla$ is primarily used in the cultivation of rice.

(A) Biofertilizers are organisms that enrich the nutrient quality of the soil.
$Rhizobium$ is a symbiotic nitrogen-fixing bacterium.
$Nostoc$ is a cyanobacterium that fixes atmospheric nitrogen.
$Mycorrhiza$ is a symbiotic association between a fungus and the roots of higher plants,which helps in phosphorus absorption.
$Agrobacterium$ is a soil bacterium known for its ability to transfer $DNA$ into plant cells,commonly used in genetic engineering as a vector,but it is not classified as a biofertilizer.

(C) Bacteria,particularly nitrogen-fixing bacteria like $Rhizobium$,$Azotobacter$,and $Clostridium$,are highly useful for soil fertility. These organisms convert atmospheric nitrogen into ammonia,which plants can absorb and utilize for growth. This process is known as biological nitrogen fixation,which significantly enriches the soil with essential nutrients.

(C) Soybean is a leguminous plant. $Rhizobium$ is a symbiotic nitrogen-fixing bacterium that forms root nodules in leguminous plants like soybean. It converts atmospheric nitrogen into ammonia,which the plant can utilize for growth,thus acting as an effective biofertilizer. Therefore,the correct option is $C$.

(B) Bio-fertilizers are organisms that enrich the nutrient quality of the soil. The main sources of bio-fertilizers are bacteria,fungi,and cyanobacteria. These microbes fix atmospheric nitrogen,solubilize phosphorus,and produce plant growth-promoting substances,thereby enhancing soil fertility naturally.

(D) Biofertilizers are organisms that enrich the nutrient quality of the soil.
$1$. $Azolla-Anabaena$ is a symbiotic association where the cyanobacterium $Anabaena$ fixes nitrogen for the $Azolla$ fern.
$2$. $Mycorrhiza$ is a symbiotic association between fungi and roots of higher plants,which helps in phosphorus absorption.
$3$. $Legume-Rhizobium$ symbiosis is a classic example where $Rhizobium$ bacteria fix atmospheric nitrogen in the root nodules of leguminous plants.
Since all these examples represent biological agents used to increase soil fertility,the correct answer is $All \text{ of the above}$.

(C) $Azolla$ is a small aquatic fern that has a symbiotic relationship with the nitrogen-fixing cyanobacterium $Anabaena$ $azollae$.
This cyanobacterium lives in the leaf cavities of $Azolla$.
When $Azolla$ is grown in rice fields,it acts as a biofertilizer by fixing atmospheric nitrogen,which significantly increases the availability of nitrogen to the rice plants.
Studies have shown that the use of $Azolla$ as a biofertilizer can increase rice production by up to $50\%$.

(C) Biofertilizers are organisms that enrich the nutrient quality of the soil.
$BGA$ (Blue-Green Algae) like $Anabaena$ and $Nostoc$ are known for their nitrogen-fixing capabilities.
$VAM$ (Vesicular-Arbuscular Mycorrhiza) is a type of mycorrhiza that helps in the absorption of phosphorus from the soil.
Therefore,both $BGA$ and $VAM$ are classified as biofertilizers.

(C) The correct answer is $C$.
$VAM$ stands for Vesicular-Arbuscular Mycorrhiza,which is a type of symbiotic association between fungi and plant roots that helps in phosphorus absorption.
It is a biofertilizer,not a mycoherbicide.
$Azospirillum$ is a nitrogen-fixing bacterium associated with maize.
$Mycorrhiza$ forms a symbiotic relationship with $Pinus$ roots.
$Rotenone$ is a naturally occurring chemical compound used as an insecticide.

(A) Mycorrhiza is a symbiotic association between a fungus and the roots of higher plants. The fungal symbiont in these associations absorbs phosphorus from the soil and passes it to the plant. It also provides other benefits such as resistance to root-borne pathogens,tolerance to salinity and drought,and an overall increase in plant growth and development. Among the given options,the primary mechanism for stimulating growth is the absorption of inorganic ions (specifically phosphorus) from the soil.