The structures that line up the chromosomes on the equatorial plate during metaphase are called-

Options

A. Asters
B. Polar and Kinetochore microtubules
C. Centrosomes
D. Centrioles

Answer

**Step-by-Step Solution:**

1. **Understanding Metaphase**: During metaphase, chromosomes align at the equatorial plate of the cell. This is a crucial step in cell division, ensuring that each daughter cell will receive an identical set of chromosomes.

2. **Identifying Key Structures**: The structures responsible for aligning the chromosomes are known as spindle fibers. These are formed from microtubules, which are protein structures that play a key role in cell division.

3. **Role of Kinetochore**: Each chromosome has a specialized region called the kinetochore, which is a proteinaceous disk. The kinetochore is essential for the attachment of spindle fibers to the chromosomes.

4. **Formation of Spindle Fibers**: The spindle fibers are made up of microtubules that extend from the centrioles (the organizing centers for microtubules) to the kinetochores of the chromosomes. This connection is vital for the movement of chromosomes during cell division.

5. **Conclusion**: Therefore, the structures that line up the chromosomes on the equatorial plate during metaphase are called spindle fibers, which include both polar microtubules and kinetochore microtubules.

**Final Answer**: The structures that line up the chromosomes on the equatorial plate during metaphase are called spindle fibers.

---