Symbiotic biological nitrogen fixation Questions in English

(C) Root nodules are specialized structures found on the roots of leguminous plants.
These nodules house symbiotic nitrogen-fixing bacteria known as $Rhizobium$.
$Rhizobium$ bacteria infect the root hairs of leguminous plants,leading to the formation of nodules where they convert atmospheric nitrogen into ammonia,which the plant can utilize for growth.

(C) The symbiotic nitrogen-fixing bacteria that live in the root nodules of leguminous plants belong to the genus $Rhizobium$.
These bacteria form a mutualistic relationship with the plants,where the bacteria fix atmospheric nitrogen into ammonia,which the plant can use for growth,while the plant provides the bacteria with carbohydrates and a protected environment.

(A) Nitrogen-fixing bacteria,such as $Rhizobium$,form a symbiotic relationship with the roots of plants belonging to the family $Leguminosae$ (also known as $Fabaceae$).
These bacteria reside in root nodules,where they convert atmospheric nitrogen into ammonia,which the plant can utilize for growth.
This mutualistic association is a characteristic feature of leguminous plants.

(D) The bacterium $Frankia$ is a well-known nitrogen-fixing organism that forms symbiotic associations with non-leguminous plants (such as $Alnus$). While $Azospirillum$ is a nitrogen-fixing bacterium,it is Gram-negative. $Rhizobium$ is associated with leguminous plants. $Nitrosomonas$ is involved in nitrification,not nitrogen fixation. Therefore,$Frankia$ is the correct answer in the context of non-leguminous nitrogen-fixing bacteria.

(D) $Nitrosomonas$,$Nitrobacter$,and $Nitrosococcus$ are nitrifying bacteria involved in the nitrogen cycle (converting ammonia to nitrite or nitrite to nitrate),but they do not fix atmospheric nitrogen.
$Rhizobium$ is a symbiotic bacterium that lives in the root nodules of leguminous plants and has the enzyme nitrogenase,which allows it to fix atmospheric nitrogen into ammonia.

(C) The symbiotic association of the actinomycete $Frankia$ with the roots of non-leguminous plants (such as $Alnus$) leads to the formation of root nodules. These nodules are capable of nitrogen fixation. While $Rhizobium$ is associated with leguminous plants,$Frankia$ is specifically known for its role in non-leguminous nitrogen-fixing trees.

(A) $Rhizobium$ is a symbiotic nitrogen-fixing bacterium that lives in the root nodules of leguminous plants.
It possesses the enzyme nitrogenase,which allows it to convert atmospheric molecular nitrogen $(N_2)$ into ammonia $(NH_3)$,a form that can be utilized by the plant for growth and development.
Other options like $Spirogyra$ (algae),$Mucor$ (fungi),and $Methanococcus$ (archaea) do not possess the capability to fix atmospheric nitrogen.

(A) The bacteria found in the root nodules of leguminous plants (family $Leguminosae$ or $Fabaceae$) are $Rhizobium$.
These bacteria live in a symbiotic relationship with the roots of leguminous plants.
They fix atmospheric nitrogen into ammonia,which the plant can use for growth and development.
$Azotobacter$ is a free-living nitrogen-fixing bacterium,and $Nitrobacter$ is involved in the process of nitrification (converting nitrite to nitrate).

(B) The enzyme $Nitrogenase$ is responsible for biological nitrogen fixation. In cyanobacteria like $Nostoc$,nitrogen fixation occurs in specialized,thick-walled cells called $Heterocysts$. These cells provide an anaerobic environment necessary for the activity of the $Nitrogenase$ enzyme,which is highly sensitive to oxygen.

(C) The correct answer is $C$. Root nodules of leguminous plants contain symbiotic nitrogen-fixing bacteria known as $Rhizobium \, leguminosarum$.
These bacteria fix atmospheric nitrogen into ammonia,which the plant can utilize for its growth.
In exchange,the plant provides the bacteria with carbohydrates (food) and a protected environment (shelter).
This mutually beneficial relationship between the plant and the bacteria is known as mutualistic symbiosis.

(B) Nodulated roots are characteristic of leguminous plants,which contain symbiotic nitrogen-fixing bacteria like $Rhizobium$ in their root nodules.
These bacteria fix atmospheric nitrogen into ammonia,which is then utilized by the plant to synthesize amino acids.
Since amino acids are the building blocks of proteins,leguminous plants become rich in proteins.
Therefore,the correct option is $(b)$.

(C) The relationship between nitrogen-fixing bacteria (such as $Rhizobium$) and leguminous plants is a classic example of symbiosis.
$1$. The bacteria reside in the root nodules of the legume and fix atmospheric nitrogen into ammonia,which the plant can utilize for growth.
$2$. In exchange,the leguminous plant provides the bacteria with carbohydrates (food) and a protected environment (shelter) within the root nodules.
$3$. Since both organisms benefit from this association,it is defined as mutualistic symbiosis.

(D) $Cajanus$ $cajan$ (Pigeon pea) is a leguminous plant belonging to the family $Fabaceae$ (formerly $Leguminosae$).
It possesses root nodules that contain symbiotic nitrogen-fixing bacteria,such as $Rhizobium$.
These bacteria convert atmospheric nitrogen into ammonia,which the plant can utilize,allowing it to grow well even in nitrogen-deficient soil.

(C) Plants produce their food in the form of carbohydrates through the process of photosynthesis.
Since the bacterium lives in the root nodules and relies on the host plant for nutrition,it absorbs these carbohydrates as its primary energy source.

(A) The bacterium $Rhizobium$ $leguminosarum$ lives symbiotically in the root nodules of leguminous plants like pea ($Pisum$ $sativum$).
These bacteria possess the enzyme nitrogenase,which is responsible for the biological nitrogen fixation,converting atmospheric nitrogen $(N_2)$ into ammonia $(NH_3)$.

(B) Members of the bean family (Fabaceae) possess root nodules that contain symbiotic nitrogen-fixing bacteria,such as $Rhizobium$.
These bacteria convert atmospheric nitrogen into ammonia,which is then oxidized into nitrates by soil bacteria.
This process enriches the soil with nitrogenous compounds,which are essential nutrients for plant growth.
Therefore,planting these crops helps restore soil fertility,making them crucial for crop rotation.

(B) $Rhizobium$ is a nitrogen-fixing bacterium that forms a symbiotic relationship with the roots of leguminous plants,such as gram ($Cicer$ $arietinum$).
This symbiotic association leads to the formation of root nodules,where the bacteria fix atmospheric nitrogen into ammonia for the plant.

(C) Legume plants are important because they form a symbiotic relationship with nitrogen-fixing bacteria such as $Rhizobium$ in their root nodules.
These bacteria convert atmospheric nitrogen $(N_2)$ into ammonia,which is then utilized by the plant.
This process,known as biological nitrogen fixation,enriches the soil with nitrogenous compounds,thereby increasing soil fertility.
Therefore,the correct statement is that they increase soil fertility.

(D) The bacterium $Rhizobium$ infects the roots through the root hairs of the groundnut plant and reproduces within the cortical cells of the roots.
Simultaneously,the division of cortical cells occurs,which leads to the formation of knot-like structures known as nodules in the roots.
These nodules are the sites where nitrogen fixation takes place.

(C) $Rhizobium$ is a well-known symbiotic nitrogen-fixing bacterium.
It forms a symbiotic relationship with the root nodules of leguminous plants.
In this association,the bacteria fix atmospheric nitrogen into ammonia for the plant,while the plant provides carbohydrates and a protected environment for the bacteria.

(D) $Frankia$ is a symbiotic bacterium that forms root nodules in several non-leguminous plants,such as $Casuarina$ and $Alnus$ $(Alder)$.
Unlike $Rhizobium$,which is associated with leguminous plants,$Frankia$ specifically associates with non-legumes to fix atmospheric nitrogen.

(B) $Azolla$ $pinnata$ is a small aquatic fern that maintains a symbiotic relationship with the cyanobacterium $Anabaena$ $azollae$.
This nitrogen-fixing organism resides in the specialized leaf cavities of the fern,providing fixed nitrogen to the plant in exchange for carbohydrates and a protected environment.

(C) $Sesbania$ $rostrata$ is a unique legume that forms a symbiotic association with two nitrogen-fixing bacteria: $Rhizobium$ (which forms nodules on the roots) and $Aerorhizobium$ (which forms nodules on the stem).
This dual symbiosis allows the plant to fix nitrogen more efficiently in waterlogged conditions.

(A) The nitrogen-fixing symbiotic association in the root nodules of non-leguminous plants (such as $Alnus$) is formed by the actinomycete bacterium $Frankia$.
$Rhizobium$ is typically associated with leguminous plants.
$Azotobacter$ is a free-living nitrogen-fixing bacterium.
$Thiobacillus$ is involved in the nitrogen cycle (denitrification) but does not form root nodules.

(B) Leguminous plants,such as peas and beans,form a symbiotic relationship with nitrogen-fixing bacteria,specifically $Rhizobium$. These bacteria reside in specialized structures called root nodules found on the roots of the plants. The bacteria convert atmospheric nitrogen into ammonia,which the plant can utilize for growth,while the plant provides the bacteria with carbohydrates and a protected environment.

(C) Leghaemoglobin is a reddish pigment found in the root nodules of leguminous plants.
It is specifically located around the bacteroids within the infected cells of the root nodule.
The primary function of leghaemoglobin is to act as an oxygen scavenger,maintaining a low oxygen concentration to protect the oxygen-sensitive enzyme nitrogenase,which is essential for nitrogen fixation.

(B) The symbiotic nitrogen fixation in the root nodules of leguminous plants is carried out by the bacterium $Rhizobium$.
These bacteria form a symbiotic relationship with the roots of legumes,where they reside in root nodules.
They convert atmospheric nitrogen into ammonia,which the plant can utilize for growth,while the plant provides the bacteria with carbohydrates and a protected environment.

(B) $Rhizobium$ is a symbiotic nitrogen-fixing bacterium that specifically forms root nodules in leguminous plants (family $Fabaceae$).
Wheat is a cereal crop belonging to the family $Poaceae$.
Since $Rhizobium$ does not form a symbiotic association with wheat plants,inoculating a wheat field with $Rhizobium$ will not result in nitrogen fixation.
Therefore,there will be no significant effect on the nitrogen content of the soil.

(A) Leguminous plants form a symbiotic relationship with nitrogen-fixing bacteria,such as $Rhizobium$.
These bacteria reside in specialized structures called root nodules found on the roots of the leguminous plants.
Inside these nodules,the bacteria convert atmospheric nitrogen into ammonia,which the plant can utilize for growth.
Therefore,the correct mechanism is the presence of specialized bacteria in their roots.

(B) $Leghaemoglobin$ is a red-colored pigment found in the root nodules of leguminous plants,such as $Soybean$.
This pigment acts as an oxygen scavenger,which maintains a low concentration of molecular oxygen within the root nodules.
This low oxygen environment is essential because the enzyme $Nitrogenase$,which is responsible for nitrogen fixation by the symbiotic bacteria $Rhizobium$,is highly sensitive to oxygen and gets inactivated in its presence.

(C) Nitrogen fixation in the root nodules of $Alnus$ is performed by the symbiotic bacterium $Frankia$.
$Frankia$ is a filamentous,nitrogen-fixing bacterium that forms symbiotic associations with the root nodules of several non-leguminous plants,such as $Casuarina$ (Australian pine),$Myrica$,and $Alnus$.

(C) Leghemoglobin is an oxygen-scavenging pigment found in the root nodules of leguminous plants.
It is synthesized by the symbiotic relationship between the plant and the nitrogen-fixing bacteria (like $Rhizobium$).
Its primary function is to maintain a low oxygen concentration in the nodule,which protects the oxygen-sensitive enzyme $Nitrogenase$ from being inactivated,thereby allowing efficient biological nitrogen fixation.

(B) $Azolla$ is a small aquatic fern that maintains a symbiotic relationship with the cyanobacterium $Anabaena$ $azollae$.
This cyanobacterium resides in the leaf cavities of the fern.
$Anabaena$ $azollae$ is capable of nitrogen fixation,providing fixed nitrogen to the fern,while the fern provides a protected environment and carbohydrates to the cyanobacterium.
Therefore,the correct answer is $Anabaena$.

(B) Leghemoglobin is an oxygen scavenger found in the root nodules of leguminous plants.
The enzyme nitrogenase,which is responsible for biological nitrogen fixation,is highly sensitive to molecular oxygen $(O_2)$.
Leghemoglobin creates an anaerobic environment by binding to $O_2$,thereby protecting the nitrogenase enzyme from oxidative damage and ensuring that nitrogen fixation proceeds efficiently.

(C) In plants of the family $Fabaceae$ (Leguminosae), the formation of root nodules is a complex process involving the interaction between the host plant and nitrogen-fixing bacteria like $Rhizobium$.
When the bacteria come in contact with the root hairs, they induce the root hair to curl.
The bacteria then enter the root hair and travel through an infection thread.
This infection thread reaches the inner layers of the root, specifically the $Cortex$ and $Pericycle$ cells.
The bacteria stimulate the cortical cells to divide rapidly, leading to the formation of the root nodule structure.

(B) In the root nodules of leguminous plants,the process of biological nitrogen fixation is carried out by the enzyme nitrogenase.
Nitrogenase is highly sensitive to molecular oxygen $(O_2)$ and is inactivated in its presence.
To protect the enzyme from oxygen,the root nodules contain a specialized oxygen-scavenging pigment called leghemoglobin.
Leghemoglobin creates an anaerobic environment within the nodules,which is essential for the optimal activity of nitrogenase during $N_2$ fixation.

(C) The $hup$ gene (hydrogen uptake gene) is responsible for the production of the enzyme hydrogenase in nitrogen-fixing bacteria.
This enzyme helps in the recycling of hydrogen gas produced as a byproduct during the process of biological nitrogen fixation.
The $hup$ gene is specifically found in $Rhizobium$ species,which are symbiotic nitrogen-fixing bacteria that live in the root nodules of leguminous plants.

(B) $Nitrogenase$ is a molybdenum-iron protein that catalyzes the biological nitrogen fixation process,which is the conversion of atmospheric $N_2$ into ammonia $(NH_3)$.
This enzyme is essential for the symbiotic nitrogen fixation occurring in the root nodules of leguminous plants.
If $Nitrogenase$ is inactivated,the organism or plant will be unable to fix atmospheric nitrogen.
Therefore,the process of nitrogen fixation in leguminous plants will not occur.

(C) The process of biological nitrogen fixation is carried out by the enzyme nitrogenase.
Nitrogenase is highly sensitive to molecular oxygen $(O_2)$ and requires anaerobic conditions to function effectively.
In leguminous plants,root nodules contain leghemoglobin,which acts as an oxygen scavenger to protect the nitrogenase enzyme from oxygen damage.
Therefore,the statement that nitrogenase is insensitive to oxygen is incorrect,as it is actually highly sensitive to it.

(C) $Rhizobium$ is a symbiotic nitrogen-fixing bacterium that typically forms root nodules in leguminous plants (like peas,beans,etc.).
Wheat is a non-leguminous cereal crop.
$Rhizobium$ bacteria require a specific host-plant interaction to establish nodules and fix atmospheric nitrogen.
Since wheat does not provide the necessary signals or root structures for $Rhizobium$ colonization,the bacteria will not be able to fix nitrogen in a wheat field.
Therefore,there will be no significant effect on the nitrogen content of the soil.

(D) The correct answer is $D$.
$Frankia$ is a symbiotic nitrogen-fixing bacterium that forms root nodules in non-leguminous plants like $Alnus$.
$Azolla$ is a water fern that has a symbiotic relationship with the cyanobacterium $Anabaena$ $azollae$.
$Glomus$ is a genus of arbuscular mycorrhizal fungi,which are symbiotic but not nitrogen fixers.
$Azotobacter$ is a free-living nitrogen-fixing bacterium.

(D) Nitrogen fixation is the process by which atmospheric nitrogen $(N_2)$ is converted into ammonia $(NH_3)$ or other nitrogenous compounds in the soil.
Biological nitrogen fixation is primarily carried out by microorganisms.
Symbiotic bacteria,such as $Rhizobium$ found in the root nodules of leguminous plants,play a crucial role in fixing atmospheric nitrogen into a form that plants can utilize.
Therefore,the correct option is $D$.

(C) Leguminous plants are important in agriculture because they possess root nodules containing symbiotic nitrogen-fixing bacteria like $Rhizobium$.
These bacteria convert atmospheric nitrogen into ammonia,which is a form of nitrogen that plants can absorb and utilize for growth.
This process,known as biological nitrogen fixation,enriches the soil with nitrogen,thereby increasing its fertility and reducing the need for chemical nitrogenous fertilizers.

(C) Leguminous plants,such as peas and beans,form a symbiotic relationship with the nitrogen-fixing bacterium $Rhizobium$.
These bacteria reside in specialized structures called root nodules on the roots of the leguminous plants.
The bacteria convert atmospheric nitrogen $(N_2)$ into ammonia $(NH_3)$,which the plant can utilize for growth.
Therefore,the correct statement is that leguminous plants fix $N_2$ through $Rhizobium$ bacteria living in their roots.

(C) Root nodules are specialized structures found on the roots of leguminous plants. These nodules house nitrogen-fixing bacteria such as $Rhizobium$. Among the given options, $Groundnut$ $(Arachis \text{ } hypogaea)$ is a member of the family $Fabaceae$ (legumes), which forms symbiotic associations with nitrogen-fixing bacteria to develop root nodules. Mango, $Pinus$, and $Chikoo$ do not form root nodules for nitrogen fixation.

(B) The bacteria that live symbiotically in the root nodules of leguminous plants are $Rhizobium$.
These bacteria fix atmospheric nitrogen into organic forms,which the plant uses as a nutrient,while the plant provides the bacteria with food and shelter.
This is a classic example of a symbiotic relationship.

(A) Rhizobium is a genus of Gram-negative soil bacteria that fix nitrogen. These bacteria form a symbiotic relationship with the roots of leguminous plants (such as peas,beans,and lentils). They live in root nodules and convert atmospheric nitrogen into ammonia,which the plant can use for growth,while the plant provides the bacteria with carbohydrates and a protected environment.

(C) Root nodules are specialized structures found on the roots of leguminous plants.
These nodules contain nitrogen-fixing bacteria such as $Rhizobium$.
Among the given options, groundnut $(Arachis hypogaea)$ is a member of the family $Fabaceae$ (legumes), which characteristically forms root nodules to house symbiotic nitrogen-fixing bacteria.
Apple, mango, and chikoo are not legumes and do not form root nodules.

(B) Rhizobium is a symbiotic bacterium that lives in the root nodules of leguminous plants. It fixes atmospheric nitrogen into organic forms,which the plant uses as a nutrient. This is a classic example of a symbiotic relationship where the bacteria provide nitrogen to the plant,and the plant provides carbohydrates and shelter to the bacteria.

(A) $Rhizobium$ is a well-known symbiotic nitrogen-fixing bacterium.
It forms a symbiotic association with the root nodules of leguminous plants.
In this relationship,the bacteria fix atmospheric nitrogen into ammonia for the plant,and in return,the plant provides carbohydrates and a protected environment for the bacteria.