Practice question

Batch growth exhibits four phases in closed culture: lag, log, stationary and death. Lag phase immediately after inoculation into fresh medium appears flat by cell number but represents highly active metabolic acclimatization. Cells sense new nutrient composition, pH, osmolarity and oxygen via EnvZ-OmpR and chemoreceptors, induce necessary transporters and catabolic operons such as lac when lactose present, repair oxidative damage accumulated in stationary-phase inoculum via base excision repair, and massively synthesize ribosomes, tRNAs and aminoacyl-tRNA synthetases to prepare for rapid protein synthesis. DNA replication begins but division lags, so population count remains constant while cell size, RNA to DNA ratio and protein synthesis rate increase markedly. Duration depends on inoculum age, size and medium shift magnitude. Log phase follows with exponential doubling at maximal rate, stationary arises when growth equals death due to nutrient depletion, death when viability declines. Acclimatization synonym accurately describes lag and controlling its length helps optimize fermentation start-up and antibiotic susceptibility assays where log-phase cells are targeted by wall-active agents.