→a) Describe the experiment conducted by F. Griffith in 1928 with Streptococcus pneumoniae and write the conclusions he arrived at.

→b) State the contribution of Avery, MacLeod and McCarty in providing biochemical nature to the results as obtained by Griffith.

OR

→a) Differentiate between convergent and divergent evolution by taking one suitable example of each.

→b) Explain adaptive radiation with the help of suitable examples.

• When Streptococcus pneumoniae →pneumococcus) bacteria are grown on a culture plate, some produce smooth shiny colonies →S) while others produce rough colonies →R)

• Mice infected with the S strain →virulent) die from pneumonia infection, but mice infected with the R strain do not develop pneumonia.

• Griffith was able to kill bacteria by heating them.

• He observed that heat-killed S strain bacteria injected into mice did not kill them.

• When he injected a mixture of heat-killed S and live R bacteria the mice died.

• He recovered living S bacteria from the dead mice.

• He concluded that the R strain bacteria had somehow been transformed by the heat-killed S strain bacteria.

• Some ‘transforming principle’, transferred from the heat led S strain, had enabled the R strain to become virulent.

b) Avery, MacLeod and McCarty purified bio chemicals such as proteins, DNA and RNA from the heat-killed S cells, and discovered that it was DNA alone from S bacteria that caused the R bacteria to become transformed.

OR

a)

b)

• In Galapagos Islands from the original seed-eating featured finches many other forms of finches, with altered beaks arose, enabling them to become insectivorous and vegetarian finches.

• This process of evolution of different species in a given geographical area, starting from a point and literally radiating to other areas of geography or habitats is called adaptive radiation.