Question

A Leaf of $20c{m^2}$ grows $5c{m^2}$ per hour and B Leaf of $25c{m^2}$ grows $5c{m^2}$ per hour. The relative growth rate of leaf A and B respectively is –
A. $25\%$ and $20\%$
B. $20\%$ and $25\%$
C. $50\%$ and $100\%$
D. $25\%$ and $50\%$

Answer 1

Relative growth rate is generally expressed in percentage. The relative growth rate is abbreviated as RGR. Absolute growth varies from the relative growth rate. Absolute growth is actual growth of leaf expressed in $c{m^2}$. Absolute is abbreviated as AG.

Complete step by step answer:
For leaf A:
Absolute growth i.e. increase in size is given as $5c{m^2}$ per hour. The initial size of the leaf is $20c{m^2}$ . The relative growth rate is expressed in percentage; $RGR = \dfrac{{AG}}{{initial\,size}} \times 100$ $RGR = \dfrac{5}{{20}} \times 100$. So, the relative growth rate of leaf A is $25\%$ .

For leaf B:
Absolute growth i.e. increase in size is given as $5c{m^2}$ per hour. The initial size of the leaf is $25c{m^2}$. The relative growth rate is expressed in percentage; $RGR = \dfrac{{AG}}{{initial\,size}} \times 100$ $RGR = \dfrac{5}{{25}} \times 100$ $RGR = 20\%$. So, the relative growth rate of leaf B is $20\%$. So, the correct answer is the relative growth rate of leaf A is $25\%$ and the relative growth rate for leaf B is $20\%$.
So, the appropriate answer for the given question is option A.

Note: Growth is an increase in dry mass, volume, length or increase in the area because of cell division, cell expansion or because of differentiation of cells. The relative growth rate is also called the exponential growth rate or continues growth rate which is defined as a growth rate relative to its size. Many plant physiologists use RGR to quantify the speed of plant growth.