Problem 107 - Objective Biology for NEET

Question

Dicot plant exhibits an increase in girth. It is an example of (a) Secondary growth (b) Primary growth (c) Both (a) and (b) (d) None of these

Step-by-Step Solution

Answer

(a) Secondary growth

Step 1: Defining Primary Growth

Primary growth in plants is responsible for the increase in length of the plant. It involves the growth of the plant upwards and downwards, involving organs like stems, roots, and leaves.

Step 2: Defining Secondary Growth

Secondary growth refers to the increase in the girth of the plants. This type of growth results in the progressive thickening of tree trunks, roots and such, making the plant grow wider over time.

Step 3: Determining the Correct Growth Type

Looking at the question, it's stated that the Dicot plant exhibits an increase in girth. From the definitions in the previous steps, we can conclude that this is an example of secondary growth, not primary growth, because it's the type of growth responsible for increases in girth. Thus, the correct answer to the exercise is 'Secondary growth'.

Key Concepts

Primary Growth

Primary growth in plants is essentially the first stage of growth, focusing on lengthening the plant. It mainly occurs at the tips of roots and shoots, involving specialized tissues called meristems. These meristems include:

• Apical Meristems: Found at the root and shoot tips, facilitating the elongation of cells, resulting in vertical growth.
• Primary Meristems: These develop from apical meristems and differentiate into foundational tissue systems: protoderm, procambium, and ground meristem.

This growth process is crucial for plants to effectively reach sunlight and also to extend their root systems into the soil to obtain water and nutrients. It’s worth noting that primary growth is predominant in herbaceous plants where secondary growth is minimal or absent.

Dicot Plants

Dicotyledonous plants, or dicots, represent a vast majority of flowering plants. They have certain distinct features, setting them apart from monocots:

• Two cotyledons: Dicots have two seed leaves in their embryonic stage.
• Leaf Veins: The venation pattern of their leaves is typically net-like.
• Vascular Arrangement: In dicots, vascular bundles are organized in a ring within the stem.
• Secondary Growth: Many dicots, like trees and shrubs, experience secondary growth, leading to the thickening of stems and roots.

They are incredibly diverse, occupying various habitats, and their structural complexity lends them adaptability and longevity in various environments.

Plant Anatomy

Understanding plant anatomy involves exploring the structure of plants at a cellular level, which includes knowing about various tissues and organs working together. The major components include:

• Tissues: Such as dermal, vascular, and ground tissues. Dermal tissue protects, vascular tissue (xylem and phloem) transports water, nutrients, and sugars, and ground tissue provides support and storage.
• Organs: Key plant organs include roots, stems, leaves, flowers, and fruits, each serving specific functions like nutrient absorption and photosynthesis.
• Growth Zones: Plants grow through regions called meristems, found in tips (apical meristems) and between mature tissues (lateral meristems), enabling both primary and secondary growth.

A deeper understanding of plant anatomy aids in the appreciation of their growth processes, adaptability, and functions in ecosystems, making it a cornerstone of botany and plant sciences.