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The processes of both the increase in number and the increase in mass of bacteria. Growth has three distinct aspects: biomass production, cell production, and cell survival. Biomass production depends on the physical aspects of the environment (water content, pH, temperature), the availability of resources (carbon and energy, nitrogen, sulfur, phosphorus, minor elements), and the enzymatic machinery for catabolism (energy trapping), anabolism (biosynthesis of amino acid, purines, pyrimidines, and so forth), and macromolecular synthesis [proteins, ribonucleic acid (RNA), and deoxyribonucleic acid (DNA)]. Cell production is contingent on biomass production and involves, in addition, the triggering of chromosome replication and subsequent cell division. The cells may or may not separate from each other, and the division may partition the cell evenly or unevenly. Alternatively, growth may occur by budding (unequal division). Most cells so produced are themselves capable of growing and dividing; consequently, viability is usually very high when growth conditions are favorable. Moreover, in many cases the incidence of death is surprisingly low in the absence of needed nutrients. Many bacteria differentiate into resistant resting forms (such as spores); others may simply reduce their rate of metabolism and persist in the vegetative state for long times.