Question

Which phase of growth involves rapid cell enlargement?

• A. Meristematic phase
• B. Elongation phase
• C. Maturation phase
• D. Senescence phase Correct Answer: (B) Elongation phase

Hint:

To easily remember the sequence and core features of these zones, think of it as a factory production line: 1. Meristematic $\implies$ The Manufacturing phase (making new raw cells). 2. Elongation $\implies$ The Stretching phase (inflating cell size via vacuoles). 3. Maturation $\implies$ The Specialization phase (hardening walls and assigning permanent jobs).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The root or shoot tip of a plant exhibits a distinct gradient of growth. If we examine the cells moving backward from the absolute tip, we can divide the growing region into three continuous zones or phases of growth. Each zone represents a progressive stage of cellular development, showing specific structural and metabolic changes as cells transition from newly divided units into fully functional tissues.

Step 2: Detailed Explanation:
Let's analyze the characteristics of each developmental phase to identify where rapid expansion occurs: - (A) Meristematic phase: Located at the absolute apex. The cells here are small, possess dense protoplasm with large conspicuous nuclei, and have thin primary cellulosic cell walls. Their primary function is active, continuous cell division, not expansion. - (B) Elongation phase: Located just behind the meristematic zone. As new cells are pushed into this region, they begin to take up large amounts of water, forming large internal vacuoles (increased vacuolation). This influx of turgor pressure causes a rapid expansion and enlargement of the cell, significantly increasing its length and overall volume. New wall material is also deposited to support this stretching. - (C) Maturation phase: Located further away from the apex, behind the zone of elongation. In this zone, cells stop expanding and undergo structural modifications (differentiation) to perform specific functional roles (like becoming xylem vessels or epidermal cells). - (D) Senescence phase: Represents the final developmental stage leading to metabolic decline and cellular death. Therefore, rapid cell enlargement is the defining hallmark of the Elongation phase. This matches option (B).

Step 3: Final Answer:
The phase of growth that involves rapid cell enlargement is the Elongation phase.