you are given a fairly old piece of dicot stem and a dicot root. Which of the following anatomical structures will you use to distinguish between the two.

Options

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

Answer

To distinguish between an old dicot stem and a dicot root, we can analyze their anatomical structures. Here’s a step-by-step solution:

### Step 1: Identify the Structures
We need to identify the anatomical structures present in both the dicot stem and the dicot root. The options provided are cortical cells, secondary xylem, secondary phloem, and proto xylem.

### Step 2: Understand the Function of Each Structure
- **Cortical Cells**: These are present in both stems and roots and do not provide a distinguishing feature.
- **Secondary Xylem**: This is also present in both structures and does not help in differentiation.
- **Secondary Phloem**: Similar to xylem, this is found in both and cannot be used for distinction.
- **Proto Xylem**: This is crucial for our differentiation.

### Step 3: Analyze the Position of Proto Xylem
The key difference lies in the position of the proto xylem:
- In a **dicot stem**, the proto xylem is located towards the center, or pith, of the stem. This arrangement is referred to as **endarch**.
- In a **dicot root**, the proto xylem is located towards the periphery, or outer edge, of the root. This arrangement is known as **exarch**.

### Step 4: Conclusion
Based on the position of proto xylem, we can distinguish between the old dicot stem and dicot root. Therefore, the correct anatomical structure to use for differentiation is **proto xylem**.

### Final Answer
The anatomical structure that can be used to distinguish between an old dicot stem and a dicot root is **proto xylem**.

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