What anatomical structure will you use to distinguish between old dicot stem and old dicot root?

Options

A. Secondary phloem
B. Protoxylem
C. Cortical cells
D. Secondary xylem

Answer

To distinguish between an old dicot stem and an old dicot root, we can focus on the arrangement of xylem tissues, specifically the protoxylem and metaxylem. Here’s a step-by-step explanation of how to differentiate between the two:

### Step-by-Step Solution:

1. **Identify the Structures**: The primary structures to focus on are the xylem components, specifically protoxylem and metaxylem.

2. **Examine the Dicot Stem**:
- In an old dicot stem, the protoxylem is located towards the center of the vascular bundle.
- The metaxylem, on the other hand, is positioned peripherally, towards the outer edge of the vascular bundle.

3. **Examine the Dicot Root**:
- In contrast, in an old dicot root, the arrangement is different.
- Here, the protoxylem is found at the periphery of the vascular bundle.
- The metaxylem is located centrally within the vascular bundle.

4. **Comparison**:
- By comparing the positions of protoxylem and metaxylem in both structures, we can conclude that the arrangement is the key distinguishing feature.
- In summary, the protoxylem is central in the dicot stem and peripheral in the dicot root, while the metaxylem is peripheral in the stem and central in the root.

5. **Conclusion**: Therefore, the anatomical structure that can be used to distinguish between an old dicot stem and an old dicot root is the position of the protoxylem and metaxylem.