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. Contical cells
B. Secondary xylem
C. Secondary pyloem
D. Protoxylem

Answer

To distinguish between a dicot stem and a dicot root, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of Dicot Stem and Root**:
- Dicot stems and roots have different arrangements of vascular tissues (xylem and phloem) which can be observed in a transverse section (TS).

2. **Identify the Position of Protoxylem**:
- In a dicot stem, the protoxylem is located towards the center of the stem.
- In a dicot root, the protoxylem is located towards the outer side of the root.

3. **Identify the Position of Metaxylem**:
- In a dicot stem, the metaxylem is found towards the outer side (peripheral) of the stem.
- In a dicot root, the metaxylem is located at the center of the root.

4. **Analyze the Options Given**:
- Option A: Quantical Cells - Not relevant for distinguishing between stem and root.
- Option B: Secondary Xylem - Present in both but not a distinguishing feature.
- Option C: Secondary Phloem - Present in both but not a distinguishing feature.
- Option D: Protoxylem - This is the key distinguishing feature.

5. **Conclusion**:
- Based on the position of the protoxylem in the dicot stem and root, we can conclude that the anatomical structure used to distinguish between the two is **Protoxylem** (Option D).

### Final Answer:
**Option D: Protoxylem**

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