The virulent form of the bacteria S. pneumoniae is called the S strain because it is surrounded by a polysaccharide coat that makes it appear smooth under a microscope. Sometimes the S strain mutates into a non-virulent form (called the R strain), which lacks the polysaccharide coat and appears rough. Frederick Griffith performed an experiment in which he injected mice with different combinations of these bacterial strains. Drag the labels to indicate whether the mice live or die after each injection and the explanation for each test result.

1. living s strain = mice dies

2. heat killed s strain = mice live

3. living r strain = mice live

4. heat killed s strain + living r strain = mice die

Explanation:

Options

1. living s strain

2. heat killed s strain

3. living r strain

4. heat killed s strain + living r strain

Solution

It is known that S strain of the pneumococcal bacteria has virulent properties and hence it can kill an organism but when this S strain is heated its virulent factor dies and it becomes ineffective. R strain on the other hand does not possess virulent characteristics and hence it does not affect the mice. If R virulent is mixed with heat killed S strain, the new strain is transformed virulent strain which could kill an organism.

Considering above description, the answer would be

1. living s strain = mice dies

2. heat killed s strain = mice live

3. living r strain = mice live

4. heat killed s strain + living r strain = mice die