 In this module we will talk about microbial growth kinetics that is the continuation of the second chapter of fermentation as we know that fermentation is the mass culturing of the organism especially microorganism for the sake of any desired product. So when there is a mass culture then there is a growth. So in this chapter and in the different modules we will talk about that what kind of the changes occur during the mass culturing. So first we should know about what is the growth. Growth is a very simple term that refers to any change in the state in term of number, size, volume or in any sense. So in term of microbial growth basically the growth is the ratio between the birth and the death. So as concern the growth kinetics so as we know that the growth is the ratio between the birth and the death and the kinetics is the growth with respect to the time. How it change with respect to the time? So in short we can say that change in number of the cells change in the size of the cells with respect to time. So when we talk about the change with respect to time then in short we are talking about the microbial or a growth kinetics. As concern the growth kinetics keep in mind the growth the growth is further divided into 4 different phases in general talk. Lag phase, log or exponential phase, stationary phase, death or we can say decline phase as I already told you that the growth is the ratio between birth B and the death D. So as concern the lag phase when the ratio between birth and the death will be 0 then we called as lag phase but when it more than 1 then the growth will be in a log or exponential phase but when this ratio become 1 and then it can be called as stationary phase. But when this ratio decrease than 1 it mean death increase than the birth then that we refer to as decline phase. So in next slides we will talk about all these phases in detail. As concern the lag phase, lag phase is the period of adaptation for the cells to their new environment. So in the start when we inoculate the fermenting vessel in the start time the cells try to accumulate acclimatize in the new environment and then there is no increase in the cell number. So no change in the number but they can change in their volume a little bit we can say that there is a change in the cell mass. So as concern the log phase or exponential phase in this phase the cells have adjusted to their new environment because they have already adjusted their environment in the lag phase then they are ready to multiply. We know that when we talk about the cell cycle then there is the need of some cell constituents before division. So when there is a M stage so when we talk about the log phase or exponential phase then all the cells are ready to go in M stage which we can the cell can be divided either mitotically or meotically. So in this phase the cell have adjusted their new environment and they are ready to multiply exponentially. So this can also be called as balanced growth in which all the component of the cell grow at the same time. So the growth rate is independent of the new trends. So in this amount in this phase almost all the new trends are in excess amount. So the fourth stage which we called as third stage which we called as stationary phase with the exhaustion of the new trends because when there is exponential phase then there is the maximum utilization of the sub state but during this process when there is any deficiency in the nutrients then there is effect on the birth or in the mitotical regions of the cells. So then there is a stage when we can say that the ratio between the birth and the death become equal. So at that stage we can call as the stationary phase. So in this stage cells remain active their metabolism is mostly active but this is the stage when their secondary metabolites are produced. In this diagram you can say the different phases lag phase which we called as the first stage and then is the exponential phase and then a stationary phase and the last when we say this is a decline phase. In the next slide we will see that what is the decline phase. So the decline phase in which the living organism population decrease with time due to the lack of the nutrient either by some toxic secretion secreted by the cell itself. So as I have already told that in the decline phase the death rate exceed from the birth rate.