Problem 35 - Objective Biology for NEET

Question

Cells proximal to the phase of elongation show (a) Meristematic phase (b) Maturative phase (c) Elongation phase (d) All of these

Step-by-Step Solution

Answer

(a) Meristematic phase. This phase immediately precedes the Elongation phase and hence cells in this phase are closest to it.

Step 1: Understanding cell growth phases

The process of plant cell growth consists of three stages: the Meristematic phase, the Elongation phase, and the Maturative phase. In the Meristematic phase, cells undergo mitosis, thereby increasing in number. The cells then proceed to elongate in the Elongation phase, and finally, they mature in the Maturative phase.

Step 2: Identifying the phase proximal to the elongation phase

The phase that immediately precedes the Elongation phase is the Meristematic phase where cells are rapidly dividing and increasing in number. These cells are closest to the Elongation phase.

Step 3: Selection of the correct option

Given the options (a) Meristematic phase (b) Maturative phase (c) Elongation phase (d) All of these, the correct answer is (a) Meristematic phase. This is because this phase is directly before the elongation phase, and thus, cells in this phase are proximal to the elongation phase.

Key Concepts

Meristematic Phase

The Meristematic Phase is crucial in the growth of plant cells. This is where cells are actively dividing through a process known as mitosis. During this phase, cells multiply quickly and increase in number. New cells are continuously generated, maintaining a pool of cells that can differentiate and develop into various tissues.

These cells are characterized by:

• Small size and densely packed cytoplasm
• Large and distinct nuclei
• High metabolic activity
• Thin, flexible cell walls

This phase predominantly occurs in regions known as meristems, located at the tips of roots and shoots. These areas are hotspots for plant growth, allowing plants to expand both in height and depth. Understanding this phase is critical as it lays the foundation for subsequent growth stages, including the Elongation Phase.

Elongation Phase

After the meristematic phase, cells transition into the Elongation Phase. This stage is marked by a noticeable increase in cell size. Rather than dividing, cells in this phase grow larger, primarily through water uptake.

Key activities during this phase include:

• Cell wall expansion and thickening
• Vacuole enlargement, which helps stretch the cell
• Increased synthesis of cellular components, including proteins and cell wall materials

The elongation facilitates the growth in length of roots and stems, playing a vital role in how plants reach their full height. This phase typically occurs after cells have undergone division in the meristematic phase, preparing them to enter the final maturation stage.

Maturative Phase

The Maturative Phase, the final phase of cell growth, is where cells reach their full size and functional capability. After elongation, cells undergo changes that make them specialized for their roles in the plant.

Characteristics of this phase include:

• Development of thicker and more rigid cell walls
• Differentiation into various cell types, such as xylem and phloem
• Optimization for specific functions, like nutrient transport or support

Cells achieve their final form and stop growing, although they remain active in other biological processes. This phase is essential for supporting life processes in plants, ensuring that all tissues are capable of performing needed functions effectively.