Fate of ammonia Questions in English

(B) The process of biological nitrogen fixation involves the conversion of atmospheric nitrogen $(N_2)$ into ammonia $(NH_3)$.
In plants,this ammonia is further utilized for the synthesis of amino acids.
The amino acids are the building blocks of proteins.
Therefore,the relationship follows the pathway of nitrogen assimilation: $N_2$ is converted to $NH_3$,and $NH_3$ is incorporated into amino acids.

(A) The reaction catalyzed by the enzyme $Glutamate \ dehydrogenase$ is a key step in the assimilation of ammonia in plants.
The balanced chemical equation for this reaction is:
$\alpha$-ketoglutaric acid $+ NH_4^+ + NADPH \xrightarrow{\text{Glutamate dehydrogenase}} \text{Glutamate} + H_2O + NADP^+$.
In this process,ammonia $(NH_4^+)$ reacts with $\alpha$-ketoglutaric acid in the presence of $NADPH$ to form glutamic acid (glutamate),water $(H_2O)$,and $NADP^+$. Therefore,option $A$ is the correct answer.

(C) During the process of decomposition,bacteria and fungi break down complex organic matter present in plant biomass.
This process is known as ammonification.
In this process,the organic nitrogen present in the plant biomass is converted into ammonia $(NH_3)$ or ammonium ions $(NH_4^+)$.
Therefore,ammonia is the substance released by organisms during the decomposition of plant biomass by bacteria.

(B) In plants,ammonia is converted into amino acids through two main processes: reductive amination and transamination.
Amides like $Asparagine$ and $Glutamine$ are the most important amides found in plants.
These are formed from two amino acids,namely aspartic acid and glutamic acid,respectively,by the addition of another amino group to each.
Since amides contain more nitrogen than amino acids,they are transported to other parts of the plant via xylem vessels and serve as a structural component in proteins.

(C) Assertion $(A)$ is correct because asparagine and glutamine are indeed the two most important amides found in plants,which serve as a way to transport nitrogen.
Reason $(R)$ is incorrect because these amides are formed by the addition of another $NH_2$ (amino) group to aspartic acid and glutamic acid,respectively,not an $OH^-$ group. The process involves the replacement of the hydroxyl part of the acid group with an amino group.

(D) The fixed nitrogen in leguminous plants is transported in the form of amides or ureides.
Ureides are compounds that have a particularly high nitrogen to carbon ratio.
These compounds are transported along with the transpiration stream via the xylem.
Soyabean $(Glycine max)$ is a well-known example of a plant that exports fixed nitrogen in the form of ureides.

(A) The reaction catalyzed by the enzyme Glutamate Dehydrogenase is a key process in the assimilation of ammonia in plants.
The balanced chemical equation for this reaction is:
$\alpha$-ketoglutaric acid $+ NH_4^+ + NADPH \xrightarrow{\text{Glutamate Dehydrogenase}} \text{Glutamate} + H_2O + NADP^+$.
In this reaction,$\alpha$-ketoglutaric acid reacts with ammonia $(NH_4^+)$ and a reducing agent $(NADPH)$ to form Glutamate,water $(H_2O)$,and oxidized $NADP^+$.

(N/A) $ \Rightarrow $ At physiological $pH$, ammonia is protonated to form the $NH_{4}^{+}$ ion.
$ \Rightarrow $ While most plants can assimilate both nitrate and ammonium ions, the latter is quite toxic to plants and hence cannot accumulate in them.
$ \Rightarrow $ $NH_{4}^{+}$ is used to synthesize amino acids in plants through two main processes: $(i)$ Reductive Amination and $(ii)$ Transamination.
$(i)$ Reductive Amination: In this process, ammonia reacts with $\alpha$-ketoglutaric acid to form glutamic acid as shown below:
$\alpha$-ketoglutaric acid $+ NH_{4}^{+} + NADPH \xrightarrow{\text{Glutamate Dehydrogenase}} \text{Glutamate} + H_{2}O + NADP$
$(ii)$ Transamination: This involves the transfer of an amino group from one amino acid to the keto group of a keto acid. Glutamic acid is the main amino acid from which the amino group $(-NH_{2})$ is transferred to form other amino acids. The enzyme transaminase catalyzes these reactions.
$ \Rightarrow $ The two most important amides, asparagine and glutamine, are structural parts of proteins. They are formed from aspartic acid and glutamic acid, respectively, by the addition of another amino group. Since amides contain more nitrogen than amino acids, they are transported to other parts of the plant via xylem vessels.
$ \Rightarrow $ Additionally, the nodules of some plants (e.g., soybean) export fixed nitrogen as ureides, which have a particularly high nitrogen-to-carbon ratio.

(N/A) $ \Rightarrow $ At physiological $ pH $, ammonia is protonated to form $ NH_{4}^{+} $ ions.
$ \Rightarrow $ While most plants can assimilate both nitrate and ammonium ions, the latter is quite toxic to plants and hence cannot accumulate in them.
$ \Rightarrow $ $ NH_{4}^{+} $ is used to synthesize amino acids in plants through two main processes: $ (i) $ Reductive Amination and $ (ii) $ Transamination.
$ (i) $ Reductive Amination: In this process, ammonia reacts with $ \alpha $-ketoglutaric acid to form glutamic acid as shown below:
$ \alpha $-ketoglutaric acid $ + NH_{4}^{+} + NADPH \xrightarrow{\text{Glutamate Dehydrogenase}} \text{glutamate} + H_{2}O + NADP $
$ (ii) $ Transamination: This involves the transfer of an amino group from one amino acid to the keto group of a keto acid. Glutamic acid is the main amino acid from which the amino group $ (NH_{2}) $ is transferred to form other amino acids. The enzyme transaminase catalyzes these reactions.
$ \text{Amino-donor} + \text{Amino-acceptor} \xrightarrow{\text{Transaminase}} \text{Keto-acid} + \text{New amino acid} $
$ \Rightarrow $ Additionally, two important amides, asparagine and glutamine, are formed from aspartic acid and glutamic acid by adding another amino group. Since amides contain more nitrogen, they are transported via xylem. Some plants (e.g., soybean) also export fixed nitrogen as ureides.

(N/A) Ammonia $(NH_3)$ is a vital source of nitrogen for plants.
$1$. It is the primary form of nitrogen that plants can assimilate into organic compounds.
$2$. Through the process of reductive amination,ammonia reacts with $\alpha$-ketoglutaric acid to form glutamic acid,which serves as the precursor for the synthesis of other amino acids via transamination.
$3$. It is also involved in the formation of amides like asparagine and glutamine,which are the structural components of proteins and serve as a transport mechanism for nitrogen within the plant.

(N/A) Asparagine and glutamine are two of the most important amides found in plants.
$1$. They are structurally formed from two amino acids,aspartic acid and glutamic acid respectively,by the addition of another amino group to each.
$2$. Since amides contain more nitrogen than amino acids,they are transported to other parts of the plant via the xylem vessels.
$3$. Along with the transpiration stream,these amides reach the young growing parts of the plant.
$4$. In addition to nitrogen,these compounds also carry other essential elements to the sink regions of the plant.

(N/A) $(1)$ $N_2$ represents Nitrogen gas.
$(2)$ $NH_4^+$ represents Ammonium ion.

(N/A) The biochemical events in the root nodule of a pulse plant involve biological nitrogen fixation,primarily catalyzed by the enzyme $Nitrogenase$.
$1$. The enzyme $Nitrogenase$ is a $Mo-Fe$ protein that catalyzes the conversion of atmospheric nitrogen $(N_2)$ into ammonia $(NH_3)$.
$2$. The reaction is: $N_2 + 8e^- + 8H^+ + 16ATP \rightarrow 2NH_3 + H_2 + 16ADP + 16Pi$.
$3$. The end product of this reaction is ammonia $(NH_3)$.
$4$. The fate of ammonia: At physiological $pH$,ammonia is protonated to form ammonium ions $(NH_4^+)$. While $NH_4^+$ is toxic to plants in high concentrations,it is rapidly incorporated into amino acids through two main pathways:
$(i)$ Reductive amination: $NH_4^+$ reacts with $\alpha$-ketoglutaric acid to form glutamic acid.
(ii) Transamination: The transfer of an amino group from one amino acid to the keto group of a keto acid,catalyzed by transaminases.

(A) In $Glycine \ max$ (Soybean),the product of biological nitrogen fixation is transported from the root nodules to other parts of the plant in the form of ureides. These compounds have a particularly high nitrogen to carbon ratio.

(A) When $\alpha$-ketoglutaric acid reacts with $NH_{4}^{+}$ (ammonium ion) in the presence of the enzyme glutamate dehydrogenase,it undergoes reductive amination to form glutamate.
This process is a key step in the assimilation of ammonia in plants,where inorganic nitrogen is converted into organic nitrogen.

(C) Asparagine is an amide that plays a crucial role in nitrogen assimilation and transport in plants.
It is formed by the addition of another amino group to aspartic acid,involving the enzyme asparagine synthetase.
It contains a carboxamide group as its side chain,which allows it to carry a higher ratio of nitrogen to carbon compared to other amino acids,making it an efficient form for nitrogen transport in many plant species.

(B) In plants,symbiotic nitrogen-fixing prokaryotes convert atmospheric nitrogen into ammonia. To avoid toxicity,this ammonia is rapidly converted into organic forms like amides and ureides within the root nodules. These organic nitrogen compounds are then transported to the other parts of the plant,such as the shoot,primarily through the $Xylem$.

(A) Amides such as asparagine and glutamine are formed from two amino acids,namely aspartic acid and glutamic acid,by the addition of another amino group to each. Because they contain more nitrogen than amino acids,they are transported to other parts of the plant via xylem vessels. In addition to this,they act as a storage form of nitrogen. They are structural components of plant proteins,but they are not considered functional proteins (which are typically enzymes or signaling molecules).

(A) In plants,nitrogen is primarily absorbed as nitrates or ammonium ions. Since these cannot be transported directly in large quantities,they are converted into organic forms. Amides (such as asparagine and glutamine) and ureides are the primary forms in which nitrogen is transported through the xylem and stored in plant tissues because they have a high nitrogen-to-carbon ratio.

(C) The Assertion $(A)$ is correct because plants like soybean export the fixed nitrogen in the form of ureides,which have a particularly high nitrogen to carbon ratio.
The Reason $(R)$ is incorrect because both amides and ureides are transported primarily through the xylem vessels,not the phloem sieve tubes. The phloem is primarily responsible for the translocation of sugars and organic nutrients from source to sink.