Question

The enzyme that converts atmospheric nitrogen to ammonia in the nodules of the rhizobium/plant symbiosis is The greatest source for fixing molecular nitrogen (N_2) to ammonium (NH_4^+) in terrestrial environments is Why is NH_4^+ toxic to all organisms if allowed to accumulate beyond -0.5 mM? The statement above is false - NH_4^+ is not toxic but is instead an important source of nitrogen. NH_4^+ reacts with NADPH (and NADH) to reduce the reducing power in a cell. At pH 7 in the cell, some NH_4^+ OH^- coverts to NH_3 +H_2 O and the NH_3 can freely cross the membrane. At more acidic pH (e.g., pH 5.5 of the apoplast). NH_3 + H^+ converts back to NH_4 +. The end result is dissipation of the proton motive force and membrane potential across the membrane. NH_4^+ reduces the efficiency the Calvin Cycle and blocks ATP synthesis B, C, and D contribute to the toxicity of ammonia. In most environments, the form of nitrogen that is most readily available to plants that do not have symbiotic relationships with bacteria is Conversion of highly oxidized Nitrate (NO_3^-) to highly reduced NH_4^+ is necessary for biological N assimilation, but requires lots of reducing energy and much of the reaction

Answer 1

Answer. 1.

Enzyme responsible for convertion of Nitrogen to Ammonia in nodules of Rhizobium is Metalloenzyme known as Nitrogenase. This enzyme mostly contains metal such as Iron, with sometimes Vanadium as a secondary metal. Therefore, Option 1. is correct.

Answer. 2.

The greatest source for fixing nitrogen to ammonium ion in terresterial environents is by Biological fixation by Prokaryotes by Nitrogen Cycle. The correct option is 3.

Answer. 3. The option 5 is correct. Higher levels of ammoni is very toxic to plants and it effects their metabolism. It causes extensive photoinhibition thus effecting Calvin cycle. It also uncouples Photosynthetic phosphorylation. It can also freely cross the membrane and forming ammonium ions at acidic pH resulting in dissipation of proton motive force and membrane potential across the mebrane.

Answer. 4. The Dinitrogen is the form of Nitrogen readily available to plants that do not have symbiotic relationship with the bacteria. The correct option is 1.