Question

Draw a picture of the bacterial growth curve chart. Label each section and describe what is occurring in each section.

Answer 1

The bacterial growth curve has four main phases , which are as follows.....

i. Lag phase :- During the lag phase , there is no increase in cell number . It is a period of adaptation of cells to a new environment. There is no change in number , but an increase in mass. Thus in this phase , the bacterial cells are not dormant. The length of the lag phase is determined in part by the characteristics of the bacterial species and in part by conditions in the media.

ii. Log or Exponential phase :- In this phase the bacterial cells are divided and the rate of increase of cells in the culture is proportional to the number of cells present at any particular time. During exponential growth , the number of cells increases in the geometric progression i.e 2⁰ , 2¹ , 2² , 2³ until , after n divisions, the number of cells is 2 to the power n. Basically this phase completed in almost 8 hours , though it varies in different species.

iii. Stationary phase :- In this phase , the cell growth rate has leveled off and become constant. The number of cells multiplying equals the number of cells dying.

iv. Decline phase :- In this phase the number of viable cells decreases exponentially due to exhaustion of nutrients. But the total number of cells remain constant.