Question

Define absolute and relative growth rates.

Answer 1

Measurement of growth per unit time is known as growth rate. Absolute growth rate and relative growth rate are types of growth rate.

Complete Answer:
A Set of concepts and equations by which changes in size of plants over time can be dissected in component variables and summarized is called analysis of plant growth rate. It can be used to analyse crop growth followed over time but is often applied to analyse growth of individual plants. Size evaluation of plants after a certain period of growth, typically from the time of germination is the simplest type of growth analysis. Size is measured as dry mass of whole plants. Nowadays, the amount of green pixels derived from photographs of a plant, taken from different directions is also being used to estimate plant size.
In absolute growth rate, the plant size can be determined at more than one occasion. The increase in size over a particular time period can be easily determined. AGR is not constant in plant growth phases.
The Absolute Growth Rate (AGR) is given by- $RGR = \dfrac{{ln({M_2}) - ln({M_1})}}{{{t_2} - {t_1}}}$
After germination, the increase of biomass will be more or less proportional to the already present mass of the plant when the resources are available in enough quantity. Small just after germination which gradually increases with the growth in the plant. This measurement is known as the relative growth rate (RGR), its unit is $mgg^{−1}$ $day^{−1}$.
It is given by- $RGR = \dfrac{{ln({M_2}) - ln({M_1})}}{{{t_2} - {t_1}}}$

Note: The measurement of total growth per unit time and its comparison is known as absolute growth while the growth of a particular system per unit time is called relative growth rate, it is expressed on a common basis.