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Explain Griffith’s transformation experiments. Whatdid he conclude from them? a. Two strains of S. pneumoniae were used for the experiment. Griffith injected a mouse with heatinactivated S strain (pathogenic) and R strain (non- pathogenic). The mouse died and S strain was recovered from the dead mouse. He concluded that external DNA is taken up by a cell that changed morphology and physiology. b. Two strains of Vibrio cholerae were used for the experiment. Griffith injected a mouse with heatinactivated S strain (pathogenic) and R strain (non- pathogenic). The mouse died and S strain was recovered from the dead mouse. He concluded that external DNA is taken up by a cell that changed morphology and physiology. c. Two strains of S. pneumoniae were used for the experiment. Griffith injected a mouse with heatinactivated S strain (pathogenic) and R strain (non- pathogenic). The mouse died and R strain was recovered from the dead mouse. He concluded that external DNA is taken up by a cell that changed morphology and physiology. d. Two strains of S. pneumoniae were used for the experiment. Griffith injected a mouse with heatinactivated S strain (pathogenic) and R strain (non-pathogenic). The mouse died and S strain was recovered from the dead mouse. He concluded that mutation occurred in the DNA of the cell that changed morphology and physiology.

Step by step solution

01

- Identify the aim of Griffith’s experiments

Griffith aimed to understand how certain strains of bacteria could cause disease. He worked with two strains of S. pneumoniae: a virulent S strain (which causes disease) and a non-virulent R strain (which does not cause disease).

02

- Describe the experimental setup

Griffith injected mice with different combinations of live and heat-killed bacteria. Specifically, he injected a mouse with heat-killed S strain and live R strain of S. pneumoniae.

03

- Observe the outcome

The mouse injected with the heat-killed S strain and live R strain died. Upon examining the dead mouse, Griffith recovered live S strain bacteria from its body.

04

- Analyze the results

The recovery of live S strain bacteria meant that the non-virulent R strain had somehow been transformed into the virulent S strain. This indicated that some 'transforming principle' from the dead S strain had been taken up by the R strain, altering its characteristics.

05

- Conclude Griffith’s findings

Griffith concluded that the 'transforming principle' was responsible for transferring genetic information, causing the non-virulent R strain to become virulent. He suggested that external DNA could be taken up by a cell, leading to changes in its morphology and physiology.

06

- Choose the correct conclusion from the given options

Option a is the correct choice. Griffith concluded that external DNA is taken up by a cell, changing its morphology and physiology, after injecting a mouse with heat-killed S strain and live R strain, and recovering live S strain from the mouse.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

S. pneumoniae

Streptococcus pneumoniae, commonly referred to as S. pneumoniae, is a type of bacteria responsible for various infections, including pneumonia. This bacterium has two main strains:
- The virulent S strain, which is pathogenic and causes disease.
- The non-virulent R strain, which does not cause disease.
These strains have different characteristics in terms of their external appearance and effects on organisms. In Griffith's experiments, these differences played a crucial role in understanding how genetic material could be transferred between organisms.

transforming principle

The 'transforming principle' was a term used by Griffith to describe the mysterious substance that caused the non-virulent R strain of S. pneumoniae to become virulent. This principle was later identified as DNA. Griffith's discovery was groundbreaking because it suggested that DNA carried genetic information and could be transferred from one organism to another, thereby transforming its properties.
- He found that the non-virulent R strain could take up some factor from the heat-killed S strain.
- This uptake changed the R strain's characteristics, making it virulent.
These findings provided early evidence that DNA, and not protein, was the material responsible for heredity.

genetic transformation

Genetic transformation is a process by which an organism takes up external DNA and integrates it into its own genetic material, leading to changes in its morphology and physiology. Griffith's experiments were among the first to demonstrate this process in bacteria.
- Non-virulent R strain bacteria transformed into virulent S strain when mixed with heat-killed S strain bacteria.
- This transformation showed that genetic material from the S strain was transferred to the R strain.
With Griffith's findings, scientists began to understand that genetic transformation allowed for the transmission of new traits between organisms, a pivotal concept in genetics.

bacterial strains

Bacterial strains refer to variants or subtypes of bacteria. In Griffith's experiments, two strains of S. pneumoniae were used: the S strain and the R strain. These strains were distinct in their ability to cause disease and in their physiological characteristics.
- The S strain had a smooth appearance due to a polysaccharide capsule and was virulent.
- The R strain lacked this capsule, appeared rough, and was non-virulent.
When Griffith mixed live R strain bacteria with heat-killed S strain bacteria, the R strain took up the 'transforming principle' and became virulent. This illustrated how bacterial strains could change properties through genetic transformation.