Growth is an irreversible increase in size, mass, volume, number and weight of an entire organism or its parts.
Growth can be measured in various ways, like Arithmetic growth and Geometric growth. In the former one, the rate of growth is constant and growth takes place in arithmetic progression (like 2, 3, 4, 5,... etc). In the latter, growth takes place in geometric progression (like 2, 4, 8, 16, 32, ... etc.). This type of growth is common in unicellular organisms.
Growth curves represent the graphical representation of the rate of growth with respect to time as a function. There are two main types of growth curves:
1. The linear curve represents the arithmetic growth pattern. This is seen in meristematic apices of root and shoot of plants.
2. The sigmoid curve is the most common type of growth curve. It has three phases:
A. The lag phase is the phase where the growth rate is minimum.
B. The Log or Exponential phase is the phase in which the growth rate is extremely rapid. This allows the growth to occur to the maximum and the number reaches to the maximum. This is also called as the Grand period of Growth.
C. The stationary phase or steady-state represents a decline in the growth rate. This happens because of the resources, which are exhausted by the increased number. This phase also represents the maturity of growth.
