Problem 147 - Objective Biology for NEET

Question

Lenticels are formed in bark, which are (a) Aerating pores (b) Made up of phloem (c) Made up of xylem (d) Found in monocot plants

Step-by-Step Solution

Answer

The correct answer is (a) 'Aerating pores'.

Step 1: Understand the Question

First, it's essential to know what lenticels are. Lenticels are small, corky pores or openings in the bark of woody stems and roots of plants. They allow for direct gas exchange between the internal tissues and atmosphere through the bark, which is otherwise resistant to gas exchange.

Step 2: Evaluate the Options

Now, let's evaluate each option. (a) 'Aerating pores' - Yes, this fits the description of lenticels as it allows for gas exchange. (b) 'Made up of phloem' - No, lenticels are not made up of phloem. They contain loosely arranged cells of the periderm. (c) 'Made up of xylem' - No, lenticels are not made up of xylem. (d) 'Found in monocot plants' - No, lenticels are not typically found in monocots, but more commonly in woody dicot plants.

Step 3: Select the Correct Option

After evaluating all the options, it's clear that option (a) 'Aerating pores' most accurately describes the lenticels according to their structure and function. Hence, (a) is the correct answer.

Key Concepts

Gas Exchange in Plants

Plants, similar to animals, require oxygen for respiration and release carbon dioxide as a waste product. However, plants, being sessile organisms, have developed unique structures for the exchange of gases with their environment. One such adaptation is the presence of lenticels, which are prominently involved in this gas exchange process.

Lenticels, the small openings on the bark of woody plants, facilitate the direct transfer of gases between the air and the internal tissues of the stem. They are crucial for the plant’s survival, especially when the stomata, the primary gas exchange organs found on leaves, are closed at night or during drought conditions. Through these lenticels, plants can continue to respire. Moreover, they help to release internal ethylene, which is a hormone significant for the plant's growth and development.

Structure of Woody Stems

Understanding the structure of woody stems is fundamental to grasping the function of lenticels. Woody stems are composed of several layers, each with specific roles. The core of the stem contains the xylem, responsible for transporting water and minerals from roots to leaves. Surrounding the xylem is the phloem, which distributes sugars and other products of photosynthesis throughout the plant.

The outer layers consist of a protective covering called bark, which itself is composed of the periderm, the phloem, and the cortex. The periderm includes the outer cork layer and an inner layer of cork cambium. Lenticels arise within the periderm as the cork cells die, leaving behind openings that permeate the otherwise impervious cork layer. Therefore, the availability of lenticels allows the otherwise enclosed woody stem to exchange gases with the environment.

Functions of Bark in Plants

The bark of a plant is not just an idle covering; it performs several vital functions. Primarily, it serves as a protective layer, shielding the plant from physical damage and parasites. It also provides insulation against extreme temperatures and reduces water loss, fostering overall plant health.

In addition to protection, bark also participates in storage and transportation. The living part of the bark, the phloem, transports nutrients produced by photosynthesis. Finally, serving as an avenue for cellular respiration, bark's role is augmented with the inclusion of lenticels, which ensure that metabolic processes continue even when other parts, like leaves, are not actively engaged in gas exchange. Thus, the functions of bark are diverse and critical, from defense to supporting life-sustaining processes like respiration through lenticels.