Where does the maximum growth in the root occur?

Movements of leaves of sensitive plant, $Mimosa \text{ } pudica$, are due to

What is the process of increasing the number and mass of cells called?

Growth of plants is different from the growth of animals in:

Assertion $(A)$: Morphogenesis and differentiation occur during the process of growth.
Reason $(R)$: The number of cells increases during growth.

$A$ rubber band stretches and reverts back to its original position. Bubble gum stretches,but it would not return to its original position. Is there any difference between the two processes? Discuss it with respect to plant growth. [Hint: Elasticity (reversible),Plasticity (irreversible)]