Yeast cells grown under laboratory conditions commonly exhibit the logistic population growth curve. There are five phases: the lag phase, the positive acceleration phase,
exponential phase, negative acceleration phase, and stationary phase.
(a) Lag phase: Initially, the population of the yeast cell is very small. This is because of the limited resources present in the habitat.
(b) Positive acceleration phase: In this phase, yeast cells adapt to the new environment and start to multiply. However, at the beginning of this phase, the growth of the cell is very limited.
(c) Exponential phase: During this phase, the population of the yeast cell increases suddenly due to rapid growth. Due to sufficient food resources, a constant environment, and the absence of interspecific competition, the population grows exponentially. As a result, the curve rises steeply upwards.
(d) Negative acceleration phase: During this phase, environmental resistance increases and the population growth rate decreases. This occurs because of an increased completion among the yeast cells for food and shelter.
(e) Stationary phase: During this phase, the population becomes constant. A population's number of cells equals its number of cells that die. Additionally, the species is said to have reached the carrying capacity of its habitat.