Problem 178 - Objective Biology for NEET

Question

In monocot roots which types of vascular bundles are found? (a) Collateral, conjoint and closed (b) Radial vascular bundle with exarch xylem (c) Bicollateral, conjoint and closed (d) Radial vascular bundle with endarch xylem

Step-by-Step Solution

Answer

The types of vascular bundles found in monocot roots are Radial vascular bundle with exarch xylem.

Step 1: Gather Knowledge about Vascular Bundles

Vascular bundles are a part of the vascular system in plants which are involved in transportation of water, nutrients and other substances. It includes xylem and phloem. There are several types of vascular bundles like Collateral, Radial, Bicollateral etc.

Step 2: Knowing about Monocot Roots

Monocot roots or monocotyledonous roots are the roots of plants with a single seed leaf. They have a specific type of arrangement of bundles.

Step 3: Matching the Options

Recall that in monocot roots, vascular bundles are usually radially arranged. The xylem is exarch, meaning that the first-formed xylem is located furthest from the periphery. The phloem is located on the outside of the xylem. Based on this, we can compare the given options.

Step 4: Final Step- Find the Correct Answer

By comparing the given options with our knowledge, we find that (b) Radial vascular bundle with exarch xylem is the correct answer as this type of bundle is found in monocot roots.

Key Concepts

Vascular Bundles in Plants

Vascular bundles are like the circulatory system of plants, acting as conduits for the transport of vital substances throughout the organism. Central to the survival of plants, these bundles consist of two main components: xylem and phloem.

The xylem is responsible for the upward movement of water and dissolved minerals from the roots to the leaves, while the phloem distributes sugars, amino acids, and other organic products of photosynthesis from the leaves to other parts of the plant where they are needed or will be stored.

The arrangement of vascular bundles can vary greatly among different types of plants. For example, dicots typically have collateral vascular bundles, where the phloem and xylem are adjacent to each other, with the phloem located towards the outside of the stem. In monocots, however, the vascular system is more complex, and the bundles are often scattered throughout the stem's cross-section. This arrangement is crucial for the plant's structure and function.

Exarch Xylem

In botany, the term 'exarch' refers to the developmental sequence of xylem, particularly in the context of roots. The xylem matures from the outside inwards in an 'exarch' arrangement. This means that the oldest xylem cells are found near the periphery of the root, and the youngest ones are closer to the center.

Significance in Monocot Roots

In monocotyledonous roots, this pattern plays a vital role as it helps in efficient water transport and supports the plant's structure. Since water and nutrients are absorbed by the root's outermost layers, having mature, fully functional xylem cells in proximity to where absorption occurs can enhance the efficiency of water uptake.

This xylem pattern contrasts with 'endarch' xylem development, in which the sequence is inverse, with the youngest xylem cells found on the outside and the maturation process moving inwards. 'Exarch' and 'endarch' xylem are terms usually associated with roots, as the pattern in stems may be different and is designated with different terminology.

Monocotyledonous Root Structure

Monocotyledonous roots, commonly referred to as monocot roots, belong to plants that are characterized by having a single cotyledon, or seed leaf, during their embryonic stage. One of the distinct anatomical features of these roots is their vascular bundle arrangement.

Monocot roots are marked by a radial arrangement of vascular bundles, where the core is made up of xylem in the shape of a star, which is surrounded by phloem. This root architecture is quite different from dicot roots, which usually have their vascular bundles arranged in a ring.

Adaptation for Stability and Absorption

The radial configuration of vascular bundles in monocot roots is an adaptation that provides stability to the plant. The 'exarch' arrangement of xylem also plays into this by ensuring that the most mature and functional xylem tissues are near the periphery, enhancing water uptake directly from the soil.

Understanding the structure of monocot roots is fundamental when studying plant anatomy, as it sheds light on how these plants manage to thrive in a variety of environments by efficiently transporting water and nutrients from the soil to the rest of the plant, thereby maintaining their physiological processes.