Problem 174 - Objective Biology for NEET

Question

Phloem parenchyma is absent in (a) Dicot root (b) Dicot leaf (c) Monocot stem (d) Dicot stem

Step-by-Step Solution

Answer

Phloem parenchyma is typically absent in the monocot stem. Hence, the correct answer is (c) Monocot stem.

Step 1: Identification of Phloem Parenchyma

Phloem parenchyma is a type of cell found in plant tissues that plays vital roles in metabolic function, storage and transport of food and nutrients within the plant body. It is commonly present in the primary phloem of vascular plants, which include both the monocots and dicots.

Step 2: Identifying Where Phloem Parenchyma is Absent

From the options presented: dicot root, dicot leaf, monocot stem and dicot stem, one has to identify where phloem parenchyma is absent. Based on typical plant anatomy, phloem parenchyma cells are generally absent in the monocot stem.

Step 3: Choosing the Answer

Given the facts from step 1 and step 2, the answer to the question is (c) Monocot stem, as this is typically the part of the plant where phloem parenchyma is absent.

Key Concepts

Plant Anatomy and the Phloem Parenchyma

Understanding the intricacies of plant anatomy is crucial when exploring the complex machinery of vascular plants. The phloem parenchyma is one such component that plays a critical role in the transport and storage of nutrients. Unique to vascular plants, phloem tissue is part of the plant's transport system, disseminating sugars and other metabolic products throughout the organism.

Typically, phloem is divided into several cell types, including sieve elements, companion cells, fibers, and parenchyma cells. Phloem parenchyma cells are specialized for storage and the lateral transport of solutes across the plant. These cells are living and when mature, retain a nucleus and are capable of metabolic functions. In contrast to other phloem cells that are directly involved in the transport of sap, parenchyma cells have a more ancillary role, modulating the plant's internal environment and storing vital nutrients and substances.

The presence or absence of phloem parenchyma can vary across plant types and even within different parts of the same plant, reflecting a diversity that is tied strongly to a plant's evolutionary adaptations and function.

Vascular Plants: A Closer Look at Their Transport System

Vascular plants, or tracheophytes, include ferns, gymnosperms like pine trees, and angiosperms encompassing both monocots and dicots. They are defined by their vascular system, which consists of the xylem and phloem tissues responsible for the conduction of water, nutrients, and organic compounds. The xylem facilitates the upward movement of water and minerals from roots to leaves, while the phloem distributes the products of photosynthesis, such as sugars from leaves to non-photosynthetic parts of the plant.

Phloem parenchyma is integral to the phloem's function, offering a flexible and dynamic storage space for plants to maintain homeostasis. It should be understood that a vascular system's complexity and efficiency are key to a plant’s ability to grow taller and thrive in a variety of environmental conditions, thereby giving vascular plants an evolutionary advantage over their non-vascular counterparts.

Monocot vs Dicot: Distinguishing Features and Phloem Parenchyma Distribution

The distinction between monocotyledons (monocots) and dicotyledons (dicots), which are subgroups within the angiosperms, is fundamental to plant biology. Monocots, such as grasses, lilies, and palms, have a single cotyledon, or seed leaf, while dicots, like roses, peas, and daisies, have two.

In addition to the number of cotyledons, there are other key differences between these two groups:

• Monocots have parallel leaf venation, whereas dicots exhibit a reticulate pattern.
• The vascular bundles in monocot stems are scattered, while in dicots they are usually arranged in a ring.
• Monocots generally have fibrous root systems, contrasted with the tap root systems of dicots.

These structural differences extend to the distribution of phloem parenchyma. As outlined in the textbook exercise, phloem parenchyma is typically absent in monocot stems. This absence serves as another distinguishing characteristic and is reflective of the evolutionary adaptations that monocots have developed to optimize their growth and survival in diverse environments.