Within the exponential phase of growth, if the initial surface area and growth rate of leaf is 10$mm^2$ and 0.015 $mm^2$ hours respectively, the area of the leaf after 4 days would range from
(A). 10-12$mm^2$
(B). 20-24$mm^2$
(C). 30-36$mm^2$
(D). 40-48$mm^2$

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Hint: Exponential growth is a form of growth of population where unlimited resources are present. When organisms go through exponential growth, the curve made by them is J-shaped or exponential. In the case of this question, if the growth can be measured in terms of hours, it should be easy enough.

Complete answer:
Let’s discuss the question and find the proper answer.
In the given question, the growth rate of the leaf is 0.015 $mm^2$ per hour
Here we have to calculate the range of growth for 4 days.
As we know, One day is equal to 24 hours, so 4 days will be 96 hours.
Now for calculating the growth of the area of the leaf, we have to multiply 0.015 with 96.
Hence, after 4 days, the total growth will be = 1.44$mm^2$
Therefore, after 4 days, the leaf area will be= (10+1.44) $mm^2$ i.e. 11.44 $mm^2$

Hence option A: 10-12$mm^2$ is the correct answer.

Note: There are mainly two types of growth of the population that are noticed. One is exponential or J-shaped that is discussed above and another one is the logistic growth curve or sigmoidal growth curve that is S-shaped. The sigmoidal growth curve has three phases including the lag phase, log phase, and stationary phase.