(N/A) Growth rate is defined as the increased growth per unit time.
Growth can be expressed mathematically and can be categorized into two main types:
$1$. Arithmetic Growth: In this type,following mitotic cell division,only one daughter cell continues to divide,while the other differentiates and matures. $A$ simple example is the elongation of a root at a constant rate. Mathematically,it is expressed as: $L_t = L_0 + rt$,where $L_t$ is the length at time $t$,$L_0$ is the length at time zero,and $r$ is the growth rate or elongation per unit time.
$2$. Geometrical Growth: In this pattern,the growth follows three distinct phases:
$(a)$ Lag phase: The initial phase characterized by very slow growth.
$(b)$ Log phase (Exponential phase): The middle phase where growth is rapid and exponential. Both progeny cells retain the ability to divide,provided nutrient supply is adequate.
$(c)$ Stationary phase: The final phase where growth slows down due to limited resources.
When the growth parameter is plotted against time,it results in a characteristic sigmoid curve. The exponential growth is expressed as: $W_1 = W_0 e^{rt}$,where $W_1$ is the final size,$W_0$ is the initial size,$t$ is the time of growth,$r$ is the relative growth rate (efficiency index),and $e$ is the base of natural logarithms.