(a) Why did Meselson and Stahl use `""^(14)N` and `""^(15)N` isotopes in the sources of nitrogen present in the culture medium in their experiment. Explain.
(b) Write the conclusion drawn by them from the experiment.

In meselson and Stahl's experiment, heavy isotope ""^(15)N was used in the from of

(a) Why did Hershey and Chase use radioactive ""^(32)P and ""^(35)S in their experiments? Explain. (b) Following the experiments conducted by them, write what conclusion did they arrive at and how?

Answer the following questions based on Meselson and Stahl's experiment of E. coli : (a) Write the name of the chemical substance used as the only source of nitrogen in the experiment. (b) Why did they allow the synthesis of the light and the heavy DNA molecules in the organism ? (c ) How did they distinguish the heavy DNA molecules from the light DNA molecules? Explain. (d) Write the conclusion the scientists arrived at, at the end of the experiment.

“Use of heavy isotope of nitrogen by Meselson and Stahl demonstrated semi-conservative mode of replication of a DNA molecule.” Explain how did they arrive at this conclusion.

In the experiment conducted by Meselson and Stahl using heavy 15N to prove semi-conservative nature of DNA, the first generation was found to have