A simple stochastic model on DNA renaturation kinetics in the presence and absence of cooperativity have been developed [the corresponding deterministic models have been explicitly treated in our previous work. Biochem Biophys Res Commun 293 (2002) 870-873]. Theoretical mean and variance of number of bases in single-stranded DNA (ssDNA), (which is of course a random variable) have been calculated and compared with the experimental values. The results showed that only the cooperative model correctly predicted the time tm at which variance becomes maximum whereas, the non-cooperative model overestimated it and thus proved the validity of the cooperative model. Some of the applications of this cooperative theory in resolving the problems of the central dogma of life, PCR etc. have also been discussed.