Problem 187 - Objective Biology for NEET

Question

Assertion: In collateral vascular bundles, the phloem is situated towards inner side. Reason: In monocot stem, cambium is present.

Step-by-Step Solution

Answer

Both the assertion and the reason are incorrect, and they are not directly connected. The phloem is not located on the inner side in collateral vascular bundles and cambium is not present in monocot stems.

Step 1: Understanding the Assertion

The assertion states that in collateral vascular bundles, the phloem is situated towards the inner side. This is incorrect. In a typical collateral vascular bundle, phloem is located on the outer side, whereas xylem is located on the inner side. This makes the assertion incorrect.

Step 2: Understanding the Reason

The reason provided is that in monocots, cambium is present. This is not entirely accurate since, in monocotyledonous plants, the vascular cambium, which is responsible for secondary growth, is not present. While some cambium-like cells may be present, they do not perform the same function as the vascular cambium in dicots. Therefore, the reason is incorrect.

Step 3: Connecting Assertion and Reason

Having established the incorrectness of both the assertion and reason, we can also note that the assertion and reason are not directly connected. Even if both were accurate, cambium's presence in monocots would not directly relate to the positioning of phloem in a collateral vascular bundle. Cambium plays a role in secondary growth, not the primary structure of vascular bundles.

Key Concepts

Collateral Vascular Bundles

In a collateral vascular bundle, the arrangement of tissues like phloem and xylem follows a specific pattern, crucial for the plant's nutrient and water transportation. Unlike the exercise statement, in such bundles, the phloem is actually positioned on the outer side while xylem is seated towards the inner side. This organization aids in effective transportation of nutrients and water throughout the plant.

• The phloem is responsible for transporting organic nutrients, primarily made during photosynthesis, from leaves to other parts of the plant.


• The xylem facilitates the movement of water and dissolved minerals from roots to the rest of the plant.

These bundles are common in both monocot and dicot stems. Their structural arrangement is crucial because they determine the pattern of growth and transport in the plant's vascular system.

Monocot Stem

A monocot stem has its own unique characteristics which differentiate it from dicot stems. The primary distinction is due to the absence of vascular cambium, meaning monocots do not engage in secondary growth in the same way as dicots. This lack of vascular cambium results in stems that do not thicken over time.
In monocots:

• The vascular bundles are scattered throughout the stem tissue rather than being arranged in a ring as in dicots.


• The bundles are usually more numerous as there is an absence of a definitive vascular cambium layer.


• This arrangement supports the plant's structural stability as it grows vertically.

Understanding these differences is essential for studying plant development and physiology, especially when determining how nutrients move through a monocot stem.

Phloem and Xylem Arrangement

Phloem and xylem are essential components in the vascular system of plants, working predominantly to transport nutrients and water. The specific arrangement of these tissues, as seen in collateral vascular bundles, serves critical roles in the plant's growth.

• Xylem: Typically positioned inward in collateral bundles, the xylem is responsible for the movement of water and dissolved minerals from the roots to other parts of the plant.


• Phloem: Located on the outer side, it transfers the organic products of photosynthesis—like sugars—from leaves to growing tissues and storage organs.

This precise arrangement ensures the plant's ability to maintain efficient transport systems, thus supporting overall plant health and facilitating the growth required to reach sunlight. Additionally, understanding how these components are organized helps explain the fundamental principles of plant anatomy and functions.