Problem 6 - Objective Biology for NEET

Question

Adventitious roots arise from part other than (a) Hypocotyl (b) Epicotyl (c) Plumule (d) Radicle

Step-by-Step Solution

Answer

The correct answer is (d) Radicle.

Step 1: Understanding Plant Parts

The Hypocotyl is a part of a plant's embryo, found in the seed, and it eventually forms the stem and leaves. The Epicotyl also contributes to the formation of upper part of the plant, like leaves. The Plumule is the part of a seed embryo that develops into the shoot bearing the first true leaves of a plant. The Radicle is the part of a plant embryo that develops into the root.

Step 2: Identifying the Site of Adventitious Roots

Adventitious roots are different from the main root system of a plant, they do not arise from the radicle, but may form from other parts like stem, old woody roots or sometimes leaves.

Step 3: Answering the Question

For the given choices, Hypocotyl, Epicotyl, Plumule and Radicle, the Radicle is the traditional origin of roots. Thus, adventitious roots arise from parts other than the Radicle. So the correct answer is (d) Radicle.

Key Concepts

Plant Embryo

A plant embryo is a young, developing plant still contained within the seed. It is a crucial early stage in the life of a plant, where it develops the essential parts needed to grow into a mature plant. Enclosed in a seed, the embryo consists of several key components:

• Cotyledons: Often referred to as seed leaves, these provide initial nutrients to the growing embryo.
• Radicle: This part eventually grows into the primary root of the plant.
• Hypocotyl: The region of the embryo that connects the cotyledons to the radicle.
• Epicotyl: The part that will develop into the shoot above the cotyledons.

Providing food and protection, the plant embryo ensures the survival of the plant after germination. As the seed absorbs water, the embryo awakens from dormancy, beginning its journey towards becoming a full-grown plant.

Hypocotyl

The hypocotyl is an integral part of the plant embryo that bridges the gap between the cotyledons and the radicle. It's sometimes described as the embryonic stem of the seedling. During germination, the hypocotyl plays a vital role in pushing upward, lifting the cotyledons and the first true leaves out of the soil, ensuring they receive sunlight and can start photosynthesis. Here's what you should know about the hypocotyl:

• The hypocotyl is positioned underneath the seed leaves (cotyledons) and above the root-bearing radicle.
• It becomes a part of the stem as the plant matures.
• In dicot plants, the hypocotyl helps in the emergence of seedlings by extending and pushing the soil aside.

The hypocotyl provides initial structural support to the young plant, setting a strong foundation for further growth, and helping the seedling stand erect.

Radicle

The radicle is the embryogenic precursor to the plant's root system. It is the first part of the plant embryo to emerge from the seed during the germination process. The radicle is crucial because it anchors the plant and absorbs water and nutrients needed for growth. When examining the role of the radicle, remember the following:

• As the plant's first root, it grows downward into the soil, tapping resources essential for survival.
• The radicle develops into the primary or taproot in many species, from which lateral roots can extend.
• Critically, adventitious roots do not originate from the radicle, which distinguishes them from the conventional root system.

Understanding the function of the radicle helps us appreciate the complexity of root formation and the integral role these structures play in plant stability and nutrition.

Epicotyl

The epicotyl is another key component of the plant embryo, lying above the cotyledons. As the plant begins to grow, the epicotyl develops into the part of the stem that is located above the first set of leaves or cotyledons. It is essential for the upward growth of the plant, driving the development of future leaves and stems. Here are some critical details about the epicotyl:

• It significantly influences the initial vertical growth trajectory of the plant after germination.
• In many plants, particularly dicots, the epicotyl elongates quickly, allowing leaf production to commence.
• The epicotyl's growth represents the start of the plant's transition from seedling to mature plant, playing a pivotal role in capturing sunlight energy for photosynthesis.

The epicotyl ensures that young plants reach upward towards the light, a necessary step for healthy growth and development. By understanding this part of the plant embryo, students can better grasp how seedlings transition into well-developed plants.