Question

Study the flow chart given below and answer the questions that follow:

1. S-strain → into mice → mice die
2. R-strain → into mice → mice live
3. Heat-killed S-strain + live R-strain → into mice → ‘A’
4. Heat-killed S-strain + DNAase + live R-strain → into mice → ‘B’

1. Name the organism and differentiate between its two strains, R and S, respectively.
2. Write the results ‘A’ and ‘B’ obtained in steps (c) and (d), respectively.
3. Name the scientist who performed the steps (a), (b) and (c).
4. Write the specific conclusion drawn from step (d).

Answer 1

1. Diplococcus pneumoniae (also known as Pneumococcus).
   Differentiation:
   • S-strain (Smooth): It has a mucous (polysaccharide) coat, appears smooth under a microscope, and is virulent (causes pneumonia).
   • R-strain (Rough): It lacks a mucous coat, appears rough, and is non-virulent (does not cause pneumonia).
2. Result ‘A’ is that the mice die, and result ‘B’ is that the mice live.
3. Frederick Griffith in 1928.
4. The specific conclusion from step (d) is that DNA is the transforming principle (genetic material).