Problem 101 - Objective Biology for NEET

Question

The plumule and radical in monocot seed are enclosed in sheaths which are called and \(\quad\) respectively. (a) Coleoptile and scutellum (b) Scutellum and coleorhiza (c) Coleoptile and coleorhiza (d) Coleorhiza and coleoptile

Step-by-Step Solution

Answer

The correct answer is (c) Coleoptile and coleorhiza.

Step 1: Understand the Biological Structure

In the seed of a monocot, the plumule (which will develop into the first leaves) and the radicle (which will develop into the root) are both enclosed in protective sheaths. The sheath covering the plumule is called the coleoptile, while the sheath protecting the radicle is termed the coleorhiza.

Step 2: Review the Provided Answers

Compare the provided terms in the exercise options with the correct terms for the sheaths covering the plumule and radicle.

Step 3: Select the Correct Answer

The option that correctly names the sheath surrounding the plumule as the coleoptile and the one surrounding the radicle as the coleorhiza is the correct answer. Therefore, option (c) 'Coleoptile and coleorhiza' is the correct answer.

Key Concepts

Understanding the Coleoptile

The coleoptile is an essential part of the monocot seed structure. It is a sheath that covers the young shoot known as the plumule. Think of the coleoptile as a protective helmet that safeguards the tender plumule as it pushes through the soil. This structure is vital as it guides the plumule upwards towards the light, which is essential for photosynthesis. To easily picture a coleoptile, imagine a tiny, pointed cap that is the first to break through the ground during a seedling’s growth.

Role of Coleoptile in Germination

During germination, the coleoptile plays a crucial role by piercing through the soil, thus facilitating the emergence of the plumule. This protective layer is particularly important as it prevents damage to the delicate parts of the emerging plant. Once the plumule emerges, the coleoptile stops growing and eventually withers away, having fulfilled its purpose of protecting the young shoot.

The Function of Coleorhiza

Closely associated with the coleoptile is the coleorhiza, which is a protective covering over the radicle, the embryonic root of the seed. Like a shield, the coleorhiza guards the radicle against mechanical injuries and other environmental stresses, such as pathogens and soil toxicity, during germination.

Importance in Seed Germination

Upon germination, the radicle is the first part of the seed that emerges, signifying the beginning of root development. The coleorhiza assists the radicle in penetrating the soil, providing anchorage for the seedling and subsequent access to water and nutrients from the soil. As the radicle grows and develops into a mature root system, the coleorhiza becomes less significant and eventually degrades.

The Significance of Plumule

The term 'plumule' might sound complex, but it simply refers to the embryonic shoot within the seed that contains the first true leaves of the plant. When the seed germinates, the plumule, as mentioned earlier, is initially protected by the coleoptile. Developing from the epicotyl – the portion of the seedling above the cotyledons – the plumule is crucial as the growth center for all the aerial parts of the plant.

Plumule’s Growth Process

After the coleoptile reaches the surface and breaks open, the plumule starts to develop the plant's initial leafy shoot. This phase is critical because it means the plant will soon be able to start photosynthesis, the process that converts light energy into the chemical energy that feeds the plant. Essentially, the plumule is like the childhood stage of a plant’s shoots, needing protection until it's strong enough to fend for itself.

Radicle: The Embryonic Root

The radicle may be considered the foundation of a plant. This embryonic root emerges from the seed during germination and establishes the plant's root system. It's the first organ that offers a lifeline to the emerging seedling by delving into the soil to absorb water and dissolved minerals, which are vital for the plant's survival and growth.

Transition from Radicle to Root System

The transition of the radicle into a full-fledged root system is a spectacle of nature. The radicle grows downwards due to a process called positive geotropism, which means it's growing in the direction of the gravitational pull. As it develops, the radicle branches out to form secondary roots, which increase the plant's ability to stabilize itself and absorb more nutrients from a broader area. Understanding the role of the radicle is fundamental in grasping the overall lifecycle of plants and the importance of proper root development for plant health.