Problem 149 - Objective Biology for NEET

Question

The bark of tree comprises of (a) All the tissues outside the vascular cambium (b) All the tissues outside the cork cambium (c) Only the cork (d) The cork and secondary cortex

Step-by-Step Solution

Answer

The bark of a tree comprises of all the tissues outside the cork cambium, hence answer (b) is correct.

Step 1: Identify Definitions

The first step is to understand what each term means. The vascular cambium is the main growth layer in the stems and roots of many plants, specifically dicots. The cork cambium also known as phellogen, is a tissue found in many vascular plants as part of the periderm.

Step 2: Apply Definitions to Options

Let's apply this understanding to each option. (a) entails all tissues that lie outside the layer in charge of substantial growth in stems and roots of plants. (b) comprises of all tissues beyond the tissue that forms part of the periderm and (c) is only considering the cork layer. (d) speaks about the cork and secondary cortex.

Step 3: Select Correct Option

The correct apprehension here is that the bark of a tree consists of all tissues outside the cork cambium, so option (b) is the most accurate description.

Key Concepts

Vascular Cambium

Understanding the role of the vascular cambium is crucial to grasp the concept of secondary growth in plants. The vascular cambium is a thin layer of meristematic tissue located between the xylem and phloem in dicotyledonous and gymnosperm plants. This dynamic layer is responsible for producing new cells that contribute to the thickness of the stem or root, a process known as secondary growth.

It comprises two types of cells: fusiform initials, which elongate and become part of the xylem and phloem, and ray initials, which maintain the radial conduction of nutrients and water. As the plant matures, the vascular cambium continuously adds layers of vascular tissue on both sides, thus contributing to the strength and girth of the plant.

• Vascular cambium contributes to plant girth
• Located between xylem and phloem
• Consists of fusiform and ray initials

Cork Cambium

The cork cambium, also known as phellogen, is another type of meristematic tissue found in many vascular plants. Unlike the vascular cambium, which adds layers inside the stem, the cork cambium focuses on generating cells that form the protective outer covering of the stem or root.

This outer layer, or bark, is comprised of the cork (phellem), the cork cambium itself, and the phelloderm. Together, they are referred to as periderm. The cork cambium produces cork cells to the outside, which eventually die and become impregnated with suberin to prevent water loss and protect against pathogens.

• Cork cambium creates external protection
• Forms cork, part of the periderm
• Cells become suberized for defense

Plant Anatomy

Plant anatomy studies the structure and organization of plant cells and tissues. It encompasses all parts of the plant, including roots, stems, leaves, flowers, fruits, and seeds. To understand secondary growth in plants, it's essential to be familiar with two primary types of growth tissues: meristems.

Meristems are regions of undifferentiated cells that have the potential to divide and differentiate into various cell types. The primary meristems—apical meristems—allow for growth in length (primary growth). In contrast, secondary meristems, such as the vascular cambium and cork cambium, allow for growth in girth (secondary growth).

• Plant anatomy involves all plant parts
• Meristems are central to growth
• Primary and secondary growth are distinct processes

Secondary Growth

Secondary growth is a characteristic of dicots and gymnosperms, wherein the plant increases in diameter. This is in contrast to primary growth, which refers to the elongation of the plant's body. Secondary growth is facilitated by two cambium layers: the vascular cambium and the cork cambium.

The vascular cambium adds to the inner layers, increasing vascular flow and structural support. On the other hand, the cork cambium produces the bark's outer protective layers. In trees, this process is evident as it leads to an increase in stem thickness and contributes to the overall robustness and longevity of the plant.

• Dicots and gymnosperms experience secondary growth
• Growth in diameter instead of length
• Vascular and cork cambia are integral to the process