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The typical growth curve for population of cells can be divided into several distinct phases called the lag phase, log phase, stationary phase and death phase.
Lag phase- When a microbial population is inoculated into a fresh medium, growth usually does not begin immediately but only after a period of time called the lag phase, which may be brief or extended depending on the
Log phase (exponential phase)In this phase - bacterial cell numbers doubles during each unit time period (i.e. generation time). For example: a culture containing 1,000 organisms per ml with a generation time of 20 minutes would contain 2,000 organisms per ml after 20 minute, 4,000 after 40 minute, 8,000 after 60 minutes, 16,000 after 120 minutes. The generation time of most bacteria is between 20 minutes to 20 hours.history of culture and growth conditions.
Stationary phase- The number of new cells produced balances the number of cells that die, resulting in a steady state. In batch culture, exponential growth cannot occur indefinitely because the essential nutrients of the culture medium are used and waste products of organisms accumulate in the environment. In stationary phase there is no net increase or decrease in cell number.
Death phase- If incubation continues after a bacterial population reaches the stationary phase, the cells may start dying. Cell death may be due to cell lysis and this is also an exponential process but much slower than that of exponential growth.