Problem 216 - Objective Biology for NEET

Question

Assertion: In dicot stem endodermis is referred as starch sheath Reason: Cells of endodermis are rich in starch grains.

Step-by-Step Solution

Answer

Yes, the reason given is a valid explanation of the assertion. The endodermis is referred to as a starch sheath because its cells are rich in starch grains.

Step 1: Understanding the Assertion

The assertion says that in dicot stem, the endodermis is referred to as starch sheath. This indicates a name or label given to the endodermis because of its characteristic.

Step 2: Understanding the Reason

The reason says that, the cells of endodermis are rich in starch grains. This is ascribing a characteristic to the cells of the endodermis.

Step 3: Establishing Correlation

The task now is to see whether the rich presence of starch grains in endodermal cells (reason) is a valid explanation for endodermis being referred to as starch sheath (assertion). If indeed the endodermis is called 'starch sheath' largely due to the presence of starch grains, then the 'reason' given is a valid explanation for the 'assertion'.

Step 4: Confirming the correlation

By comparing the assertion and the reason, it can be stated that the reason is a valid explanation of the assertion. The endodermis is called starch sheath because it is rich in starch grains.

Key Concepts

Starch Sheath

In dicot stems, the endodermis is often referred to as the "starch sheath." This term is derived from the unique characteristic of the endodermis cells being particularly rich in starch grains. The endodermis serves as a protective layer of cells that envelopes the vascular bundles within the plant stem. By calling it a starch sheath, botanists highlight the significant role it plays in storage and management of starch—an essential energy reserve for plants.
The starch sheath is crucial in regulating the movement of nutrients and water. It does so by creating a selective barrier between the central vascular tissues and the surrounding cortex. This selective control is vital for the proper functioning and growth of the plant. It helps in storage and retrieval of starch grains, which are highly concentrated in these cells due to specialized storage functions.

• Stores starch grains vital for plant metabolism
• Regulates nutrient and water distribution
• Protects the vascular system

Starch Grains

Starch grains are small granules present within the cells of a plant that act as storage units for starch, a polysaccharide that serves as a primary energy reserve. These grains are particularly abundant in the endodermis of dicot stems, hence the nickname "starch sheath." Starch in plants is similar to glycogen in animals—it’s converted from excess glucose and stored until needed for energy.
In the context of plant anatomy, the presence of numerous starch grains in the endodermal cells connects directly to the plant's ability to manage its energy reserves efficiently.
When understanding starch grains:

• They consist of amylose and amylopectin molecules
• Can be visualized using iodine staining, which gives them a characteristic blue-black color
• Play a critical role in short-term storage and energy management

Recognizing their presence in the endodermis helps to understand why it's referred to as the starch sheath.

Plant Anatomy

Plant anatomy reflects the internal structures that make up a plant, including elements such as stems, leaves, roots, and flowers. Dicot stems, specifically, consist of several distinct layers that each serve a crucial purpose for the plant's survival and growth.
Key layers within a dicot stem include:

• **Epidermis**: The outermost protective layer
• **Cortex**: Situated beneath the epidermis, storing starch and other materials
• **Endodermis (Starch Sheath)**: Functions as a regulatory barrier, rich in starch grains
• **Vascular Bundle**: Includes xylem and phloem tissues for transport of water, minerals, and nutrients

Understanding these layers not only aids in identifying plant structure but also in appreciating how they contribute to overall plant function.
Each layer has a specific job in supporting the plant's physiological processes such as nutrient distribution, growth, and storage. Appreciating these layers provides insight into why certain elements, such as the endodermis, are referred to in accordance with their function and characteristics, like being a starch sheath.