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Class 12th Biology 2016 Set3 Delhi Board Paper Solution

Question 24

Answer the following questions based on Hershey and Chases’s experiments

(a) Name the kind of virus they worked with and why ?

(b) Why did they use two types of culture media to grow viruses in ? Explain.

(c) What was the need for using a blender and later a centrifuge during their experiments ?

(d) State the conclusion drawn by them after the experiments.

Answer

(a) They worked with bacteriophage which infect bacteria because they want to discover whether it was protein or DNA from the viruses that entered the bacteria.



(b) They used two types of culture media in order to make protein of viruses radioactive with the help of 35S in one case, and DNA molecule in virus radioactive by using 32P in the other case. This was done to identify which one of the two had entered into the bacteria during viral infection.

(c) Blender was used to separate viral protein coats that – were still attached to the surface of bacteria.
Centrifuge was used to separate lighter supernatent containing viral protein coats from denser residue containing bacteria.

(d) They concluded that DNA is the genetic material that is passed from virus to bacteria.