Test: Metabolism of Nitrogen (Old NCERT) - Grade 11 MCQ

Insectivorous plants are green and otherwise autouophic plants, growing in nitrogen deficient soil. For their nitrogen nutrition, they behave like heterotrophic ayanisms. Such plants catch and digest small insects. e.g. Nepenthes, Sarracenia, Drosera, Utricularia, etc. 

Leghaemoglobin (Lb) is a red-pink pigment produced by root hair cell after being affected by Rhizobium bacteria. Leghaemoglobin regulates O₂ supply by creating anaerobic environment in the cell so that nitrogen fixing enzyme nitrogenase functions properly.

Non symbiotic nitrogen fixing bacteria, e.g., Azotobacter, Beijerinckia (both aerobic) and Bacillus, Klebsiella, Clostridium (all anaerobic) are saprotrophic bacteria that perform nitrogen fixation.

Azotobacter is a genus of usually motile, oval or spherical bacteria that form thick walled cysts, play important role in fixing atmospheric nitrogen, hence increasing fertility of soil by replenishing nitrogen in soil.

In this reaction, ammonia combines with a keto acid. The most important keto acid is the alpha ketoglutaric acid produced during the operation of Krebs cycle. The keto acid then undergoes enzymatic reductive amination to produce an amino acid. The enzyme is glutamate dehydrogenase.
Thus, the correct answer is 'i-alpha-ketoglutaric acit, ii- glutamate dehdrogenase.'

In industrial orabiological nitrogenfixation, ammonia is produced industrially by direct combination of nitrogen with hydrogen (obtained from water) at high temperature and pressure. It is then changed into various types of fertilisers including urea.

Nitrogen fixation is the conversion of inert atmospheric nitrogen or dinitrogen (N₂) into utilisable compounds of nitrogen like nitrate, ammonia, amino acids. Nitrogen fixation can be atmospheric, industrial or biological.

Ammonification is carried out by decay causing organisms. They act upon nitrogenous excretions and proteins of dead bodies of living organisms. Proteins are first broken up into amino acids. The latter are deaminated. Organic acids released in the process are used by microorganisms for their own metabolism. Examples of ammonifying bacteria are Bacillus ramosus, B. vulgaris, B. mesentericus. Streotomyces. 

Frankia is a symbiotic N₂-fixing bacterium present in the root nodulus of several non-legume plants such as Casuarine, Myrica and Alnus. Aulosira is a free-living N₂-fixing cynobacterium.

Nodulated root is the character of the pea family or leguminosae family because nodules are found for nitrogen fixation. The host plant developed specialized organs called root nodules. The host plants are mostly legumes in which symbiotic microorganism, generally a diazotrophic bacterium, reduces to ammonium. Nodulation is a host-specific process with each rhizobium having defined host-plant range.

Nitrogen is the constituent of proteins, protoplasm, nucleic acids, vitamins, hormones, etc. Nitrogen is required by all parts of a plant, particularly the meristematic tissues and the metabolically active cells.

Biological N₂-fixation is mainly carried out by Eubacteria (Bacteria and Cyanobacteria) belonging to Kingdom Monera.

Denitrification is the opposite process of nitrogen fixation in which nitrates (NO⁻₃) get converted into N₂ gas by bacteria Pseudomonas denitrificans and Thiobacillus denitrificans.

The chemical equation of nitrogen fixation can be summarised as :

ATPs  are provided by photosynthesis and respiration.

The enzyme nitrogenase is a Mo-Fe protein and catalyses the conversion of atmospheric N₂ to NH₃. If this enzyme is inactivated, then there will be no fixation of nitrogen in legumes.

Symbiotic assiciation has been found between Anabaena (blue green alga) and Azolla (a water fern). Azolla pinnata has anabeana azollae in its fronds. It is often inoculated to rice fields for nitrogen fixationl. It is an efficient fertiliser of paddy fierlds. Estimates of the annual quantities of N₂ fixed by Azolla range between 120 and 312 kg nitrogen per hactare.

It is the enzyme nitrogenase which is a Mo-Fe protein not leghaemoglobin.

Transamination is  very important reaction for amino acid biosynthesis. The reaction involves transfer of amino group from already synthesized amino acid to the keto acid. The reaction is catalyzed by enzymes called transaminases. A large number of amino acids are synthesized by this transamination reaction. Amino acids are organic molecules containing nitorgen. The incorporation of amino group from ammonium into keto acids represents the major step for synthesis of nitrogenous organic biomolecules.

Thus, the correct answer is 'Transamination.'

Frankia is a Gram-positive species of actinomycete filamentous bacterium that lives in symbiosis with actinorhizal plants of the genus Alnus. It is a nitrogen-fixing bacterium and forms nodules on the roots of non-leguminous trees. 
Thus, the correct answer is 'Frankia.'

Reduction of nitrate to nitrite is carried out by the agency of an inducible enzyme called nitrate reductase. The enzyme is a molybdoflavoprotein (with a cofactor Mo). It requires a reduced coenzyme (NADH or NADPH) for its activity. The reduced coenzyme is brought in contact with nitrate by FAD or FMN.

Nitrogen (N), phosphorus (P) and potassium (K) are referred to as critical elements for crop plants because they become easily deficient in the soil due to higher plant requirement and repeated cultivation. Nitrogen cycle is regular circulation of nitrogen amongst living organisms, with its reservoir pool in atmosphere and cycling pool in lithosphere.

Extreme of soil pH affects nodulation by reducing the colonisation of soil and the legume rhizosphere by rhizobia. Highly acidic soils (pH < 4.0) frequently have low levels of phosphorus, calcium and molybdenum and high concentration of toxic elements. While highly alkaline soils (pH > 8.0) tend to be high in sodium chloride, bicarbonate and borate, and are often associated with high salinity which reduce nitrogen fixation.

Nitrifying bacteria involves the oxidation of ammonia to nitrates through nitrites called nitrification. Nitrite bacteria (Ntirosomoncts and Nitrococcus) convert ammonia to nitrites whereas, nitrate bacteria (Nitrobacter and Nitrocystis) convert nitrite to soluble nitrates.

In Nepenthes the pitchers are meant for catching and digesting insects. The lamina is modified into pitcher. The leaf apex gives rise to a coloured lid for attracting the insects.

Leghaemoglobin is responsible for creating anaerobic conditions in the root nodules of the legume plant. It acts as an oxygen scavenger, protecting enzyme nitrogenase to come in contant with oxygen and help in the proper functioning of enzyme, i.e., conversion of atmospheric nitrogen to ammonia (NH₃).