The Question is from neet-botany molecular-basis-of-inheritance , and it was created by the author Mr. NARESH KUMAR K

Question

Which observation from Griffith's experiment with Streptococcus pneumoniae provided the strongest evidence for the existence of a 'transforming principle'?

Mr. NARESH KUMAR K · Accepted Answer

## CORE INFORMATION
✓ **Answer**: D
## CONCEPT FRAMEWORK
 **Primary Concept**: Griffith's Transformation Experiment and the discovery of DNA as the genetic material.
 **Related Topics**: Bacterial transformation, genetic material, DNA, heredity.
 **Prerequisites**: Understanding of bacterial virulence, heat killing, and experimental design.
## SOLUTION PATHWAY
**Given Information**:
  Griffith's experiment involved injecting mice with different strains of Streptococcus pneumoniae: live virulent (S), live non-virulent (R), heat-killed virulent (S), and a mixture of heat-killed virulent (S) and live non-virulent (R).
  The goal was to identify the substance responsible for transforming the non-virulent bacteria into virulent ones.
**Method & Steps**:
 1. Analyze each observation to determine its contribution to the identification of the transforming principle.
  Reasoning: The transforming principle is the substance that converts the non-virulent bacteria into virulent ones.
  Formula/Rule: None directly applicable.
 2. Evaluate each option's significance in relation to the transformation.
  Working: 
            * Option A: This observation establishes the non-virulence of the R strain, but doesn't explain the transformation.
            * Option B: This observation confirms that heat-killing eliminates the virulence of the S strain, setting the stage for the transformation experiment.
            * Option C: This observation establishes the virulence of the S strain, providing a baseline for comparison.
            * Option D: This observation demonstrates that something from the heat-killed virulent bacteria is transforming the live non-virulent bacteria into virulent ones. This is the key observation that points to the existence of a transforming principle.
  Key Point: The transformation only occurs when both heat-killed virulent bacteria and live non-virulent bacteria are present together.
 3. Conclude based on the strongest evidence for transformation.
  Result: Option D provides the strongest evidence for the existence of a transforming principle because it directly demonstrates the conversion of non-virulent bacteria into virulent bacteria through contact with a heat-killed virulent strain. This implies the transfer of genetic information.
  Verification: The subsequent experiments by Avery, MacLeod, and McCarty confirmed that the transforming principle was DNA.
 ## OPTION ANALYSIS
A :x: This observation only establishes the baseline behavior of the non-virulent strain, not the transformation process.
B :x: This observation only shows that heat kills the virulence, it doesn't explain how virulence is restored.
C :x: This observation only establishes the baseline behavior of the virulent strain, not the transformation process.
D ✓: This observation directly shows the transformation of non-virulent bacteria to virulent bacteria, providing the strongest evidence for a transforming principle.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing correlation with causation: Observing a correlation between the presence of heat-killed S bacteria and the transformation of R bacteria does not automatically prove causation.  However, further experiments confirmed this.
  2.Misinterpreting the role of heat-killing:  Understanding that heat-killing destroys the bacteria but not necessarily the genetic material is crucial.
 **Quick Tips**:
  1.Focus on the observation directly demonstrating the change in bacterial characteristics (virulence).
  2.Remember that Griffith's experiment was a crucial stepping stone in identifying DNA as the genetic material.

Mr. NARESH KUMAR K · Answer

Live non-virulent bacteria did not cause disease in mice.

Mr. NARESH KUMAR K · Answer

Heat-killed virulent bacteria did not cause disease in mice.

Mr. NARESH KUMAR K · Answer

Live virulent bacteria caused disease in mice.

Mr. NARESH KUMAR K · Answer

The correct Option is "Heat-killed virulent bacteria, when mixed with live non-virulent bacteria, caused the latter to become virulent."

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