(a) Arithmetic growth

In arithmetic growth, one of the daughter cells continues to divide, while the other differentiates into maturity. The elongation of roots at a constant rate is an example of arithmetic growth.

(b) Geometric growth

Geometric growth is characterised by a slow growth in the initial stages and a rapid growth during the later stages. The daughter cells derived from mitosis retain the ability to divide, but slow down because of a limited nutrient supply.

(c) Sigmoid growth curve

The growth of living organisms in their natural environment is characterised by an S shaped curve called sigmoid growth curve. This curve is divided into three phases – lag phase, log phase or exponential phase of rapid growth, and stationary phase.

Exponential growth can be expressed as:

${\mathrm{W}}_1={\mathrm{W}}_0{\mathrm{e}}^{\mathrm{rt}}$
$\mathrm{where},$
${\mathrm{W}}_1=\mathrm{Final} \mathrm{size}$
${\mathrm{W}}_0=\mathrm{Initial} \mathrm{size}$
$\mathrm{r}=\mathrm{Growth} \mathrm{rate}$
$\mathrm{t}=\mathrm{Time} \mathrm{of} \mathrm{growth}$
$\mathrm{e}=\mathrm{Base} \mathrm{of} \mathrm{natural} \mathrm{logarithms}$

(d) Absolute and relative growth rates

Absolute growth rate refers to the measurement and comparison of total growth per unit time.

Relative growth rate refers to the growth of a particular system per unit time, expressed on a common basis.