a. Lag phase: This phase occurs when the microbe is first introduced into a new environment or medium. During this phase, the microbe is adapting to the new conditions, synthesizing necessary enzymes, and preparing for rapid growth. The growth rate is slow or negligible during this phase.
b. Exponential phase: Also known as the log phase, this phase is characterized by rapid and exponential growth of the microbe. The conditions in the culture medium are favorable, and the microbe is utilizing available nutrients efficiently. The growth rate is at its maximum during this phase.
c. Stationary phase: In this phase, the growth rate of the microbe levels off and enters a plateau. The number of new cells being produced is balanced by the number of dying cells. The availability of nutrients becomes limited, waste products accumulate, and various factors, such as pH and crowding, contribute to the cessation of exponential growth.
d. Death phase: During this phase, the number of dying cells exceeds the number of newly divided cells. The conditions in the medium are no longer suitable for growth, and depletion of nutrients, build-up of toxic metabolites, and other adverse factors lead to cell death. The population size decreases over time.
In summary:
- Lag phase: Slow or negligible growth as the microbe adapts to new conditions.
- Exponential phase: Rapid and exponential growth of the microbe.
- Stationary phase: Growth rate levels off, reaching a plateau.
- Death phase: Number of dying cells exceeds the number of newly divided cells, leading to a decline in population size.