Answer:
The atmosphere is the largest reservoir of the nitrogen as it is composed of 78% of Nitrogen. Although 78%, this is not used by the organisms directly as the nitrogen molecule exists in nature in the form of divalent joined via triple bonds.
These triple bonds require a great amount of energy to be broken and used. Only a few prokaryotic organisms called nitrogen-fixing bacteria have the capability to break these triple bonds as they contain enzymes-nitrogenase complex which converts the atmospheric nitrogen to usable forms like ammonia, nitrates and nitrites. About 92% of the atmospheric nitrogen is fixed through this way rest through thunderstorms and Haber's process.
Thus, nitrogen-fixing bacteria is the answer.
 
        
             
        
        
        
Hi,
I think the answer you are looking for is “acid compound”.
I hope this helps. If you’d like further explanation please let me know. Also, English is not my first language, so I’m sorry for any mistakes.
        
             
        
        
        
Plant cells are bigger because they have bigger/larger Vacuoles.
These vacuoles hold water and food for the cell its like a storage for the cell.