Problem 2 - Campbell Biology

Question

The innermost layer of the root cortex is the (A) core. (B) pericycle. (C) endodermis. (D) pith.

Step-by-Step Solution

Answer

The innermost layer of the root cortex is the endodermis.

Step 1: Identify Root Cortex Layers

Understand that the root cortex has multiple layers. These layers include the epidermis, cortex, endodermis, and the pericycle.

Step 2: Inner Layer of the Cortex

The endodermis is the innermost layer of the root cortex. It acts as a selective barrier that regulates the passage of substances from the soil into the vascular tissue.

Step 3: Eliminate Incorrect Options

The pericycle is not inside the cortex, it's located just inside the endodermis. The core and pith are incorrect as they are not specific to the root cortex.

Step 4: Select the Correct Answer

Based on the identified layers, the correct answer is: (C) endodermis.

Key Concepts

Endodermis

The endodermis is the innermost layer of the root cortex. It's crucial in regulating the flow of water and nutrients from the soil into the plant's vascular system. This selective barrier ensures that only certain substances pass through. The endodermis contains a band of suberin (a waxy substance) known as the Casparian strip, which acts as a checkpoint. This helps in maintaining the plant's internal ion balance by preventing unwanted materials from entering the vascular tissues. In summary:

• Innermost layer of the root cortex
• Regulates substance flow into vascular tissue
• Features the Casparian strip, a suberin band

Root Anatomy

Root anatomy is composed of several layers, each with specific functions. At the outermost layer, you have the epidermis which is the protective skin of the root. Just inside the epidermis is the cortex, a large region responsible for storage and transport. Within the cortex lies the endodermis, followed by the pericycle. These structures organize the root for maximal efficiency in nutrient uptake and transport. The root also contains vascular tissue (xylem and phloem) that transports water, nutrients, and food throughout the plant. Key layers include:

• Epidermis: outer protective layer
• Cortex: storage and transport
• Endodermis: selective barrier
• Pericycle: just inside the endodermis

Plant Vascular System

The plant vascular system consists of xylem and phloem tissues. Xylem is responsible for carrying water and dissolved minerals from the roots to the rest of the plant. Phloem, on the other hand, transports synthesized food from the leaves to other parts of the plant. Both of these tissues work together to maintain a balance of water and nutrients essential for plant growth and survival. It's fascinating to see how this system operates as a two-way street:

• Xylem: transports water and minerals upward
• Phloem: carries food downward and upward

Pericycle

The pericycle is a layer of cells located just inside the endodermis. It plays a crucial role in the growth and development of roots. One of its primary functions is to give rise to lateral (branching) roots, ensuring that the plant can explore a greater area of soil for nutrients and water. The pericycle can also contribute to the repair of damaged vascular tissues. Therefore, it is essential for both growth and recovery:

• Located inside the endodermis
• Initiates lateral root formation
• Assists in repairing damaged vascular tissues