The logistic population growth curve is commonly observed in yeast cells that are

grown under laboratory conditions. It includes five phases: the lag phase, positive

acceleration phase, exponential phase, negative acceleration phase, and stationary

phase.

$\to$ Lag phase: Initially, the population of the yeast cell is very small. This is

because of the limited resource present in the habitat.

$\to$ Positive acceleration phase: During this phase, the yeast cell adapts to the

new environment and starts increasing its population. However, at the beginning

of this phase, the growth of the cell is very limited.

$\to$ Exponential phase: During this phase, the population of the yeast cell

increases suddenly due to rapid growth. The population grows exponentially due

to the availability of sufficient food resources, constant environment, and the

absence of any interspecific competition. As a result, the curve rises steeply

upwards.

$\to$ Negative acceleration phase: During this phase, the environmental

resistance increases and the growth rate of the population decreases. This occurs

due to an increased competition among the yeast cells for food and shelter.

$\to$ Stationary phase: During this phase, the population becomes stable. The

number of cells produced in a population equals the number of cells that die. Also,

the population of the species is said to have reached nature’s carrying-capacity in

its habitat. 

A Verhulst − pearl logistic curve is also known as an S-shaped growth curve.