Concept: This question tests your understanding of the different regions of a root tip and their specific functions, particularly focusing on the area responsible for increasing root length.

Why (D) is correct: The region of elongation is located just above the meristematic zone. Cells in this region rapidly increase in size by absorbing water and synthesizing new cell wall material, leading to a significant increase in the root's length. This elongation pushes the root tip deeper into the soil.

Why other options are wrong:

• (A) region of maturation: This region is where cells differentiate into various tissues (e.g., epidermis, cortex, vascular bundles) and mature, but it does not contribute significantly to length growth.
• (B) root cap: The root cap protects the delicate meristematic zone as the root pushes through the soil; its cells are constantly replaced but do not cause elongation.
• (C) meristematic zone: This zone contains actively dividing cells (mitosis), which produce new cells, but the primary increase in length occurs due to the elongation of these newly formed cells in the region above it.

Common Mistake: Students often confuse the meristematic zone (cell division) with the region of elongation (cell growth/increase in size) as the primary driver of root length increase.

NEET Tip / Mnemonic: Remember the order from tip upwards: Cap, Meristematic, Elongation, Maturation (CMEM). The 'E' for Elongation is where the root Extends in length.

Correct Answer: (D)