Q. 25

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Answer :

• 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.

Live virulent S-cells + Live mice Mice died

Non-virulent R-cells + Live mice Mice survived

Griffith was able to kill bacteria by heating them.

Heat Killed R-cells + Live mice Mice survived

Heat killed S-cell + Live R-Cells + Live mice Mice died

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.




• 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.

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