25.

(a) Describe the experiment performed by Griffith. What conclusions did he infer from his observations?
(b) What is artificial insemination? Mention two ways in which it is useful in breeding of dairy animals.
(c) What is single cell protein? Give its source and significance.

Grifith's experiment

They used Streptococcus pneumonia for the experiment. The bacteria occurs in two forms: smooth virulent strains and rough non-virulent forms.
They injected the mouse with the two strains and found out

When Live R Strain (non virulent bacteria) was injected in mice, the mice remained healthy.

When Live S Strain (virulent variety ) was injected into mice- the mice developed pneumonia and died.

They then killed the virulent strain by heating. When these were injected into mice, they did not develop pneumonia symptoms.
But when a mixture of Live R Strain & Killed S Strain was injected; the mice developed pneumonia and died.
They bacteria isolated from these dead mice were found to contain a mixture of live virulent and non-virulent forms. Live S strain recovered

Thus they concluded that the heat killed virulent bacteria have introduced some transforming principle/factor that has caused some non-virulent bacteria into virulent, capsulated form. This was described as Griffith effect or bacterial transformation. Later, DNA was found to be the transforming (genetic) principle that transformed R cells into live S cells. 

(b) Artificial insemination: The semen of the chosen male is collected and injected into the reproductive tract of the selected female by the breeder.

Importance in breeding of dairy animals:

Semen of healthy males can be used to inseminate a number of females.

Spread of diseases can be controlled and helps to improve a particular breed.

(c) SCP – single cell protein: Any microbial biomass/multicellular bacteria, yeast, fungi, algae which can be used as food

Source: Cyanobacteria such as spirulina / bacteria-Methyliphilus methylotrophus, filamentous fungi – Fusarium graminearum, Trichosporon cutaneum (fungus)/ bacteria
Significance:

i. Can be used as a protein rich supplement in the human diet.

ii. Helps to bridge the gap between demand and supply of protein for human diet and reduces the pressure on agriculture.

iii. Use of organic wastes and industrial effluents in raising SCP will reduce environmental pollution. Absence of pathogenicity & toxicity