Population and growth curves

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Population size and growth curves

Lag phase- Organisms are adjusting to the surrounding conditions. This may mean taking in water, cell expansion etc. The cells are active but not reproducing so population remains fairly constant.

Log phase- The population size doubles each generation as every individual has enough space and nutrients to reproduce. In some bacteria, the population can double every 20-30 minutes in these conditions. The length of this phase depends on how quickly the organisms reproduce and take up the available space and nutrients.

Stationary phase- Nutrient levels decrease and waste products like carbon dioxide and other metabolites build up. Individual organisms die at the same rate at which new individuals are being produced.

Decline/death phase- Nutrient exhaustion and increased levels of toxic waste products and metabolites lead to the death rate increasing above the reproduction rate. Eventually all organisms will die in a closed system.