Answer:
Nitrogen is present in the atmosphere in a molecule form about 78 percent. This nitrogen comes to the earth with the water through rainfall. Some nitrogen fix by beneficial microorganisms such as Cyanobacteria and Azotobactor which are present in the roots of higher plants. These microorganisms convert nitrogen molecule into nitrates and used by the plants. There are some other microorganisms which again convert nitrate into nitrogen molecules, called denitrifying bacteria and nitrogen molecule goes to the atmosphere again and complete the cycle. 
 
        
             
        
        
        
Do you mean:
In a typical cell membrane, *phospholipids* arrange themselves to form a ?
In that case, the answer is:
Bilayer
 
        
             
        
        
        
The answer for your question is preganent
        
                    
             
        
        
        
Answer:
The history of the human evolution can be studied by the fossil and DNA evidence. The similarities and advancement in certain characters has revealed the human evolution.
Different evidences like change in the diet, locomotion, brain size, walking ability as compared with the present species and species appeared 6 million years ago. The human genetics evidence and different paintings explain the culture of earlier homo species.The H. sapiens species has highly advance character that help them to survive than any other hominid species. The neanderthals extinction might occur due to their aggressive behavior, low social ability and their large cranial size.