**(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:

**w**_{1}=w_{0}e^{n}

e = Base of natural logarithms

Where,

W

1

= Final size

W

0

= Initial size

r = Growth rate

t= Time of growth

**(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.