Explanation:

During cytokinesis, the process of cell division, the spindle plays a crucial role in separating the duplicated chromosomes into two daughter cells. The spindle is a structure composed of microtubules that form during mitosis and meiosis.

Phragmoplast:
The phragmoplast is a structure that forms during cytokinesis in plant cells. It is composed of microtubules and serves as a scaffold for the construction of the cell plate, which eventually develops into the cell wall that separates the two daughter cells. The phragmoplast guides the deposition of new cell wall material and is involved in the expansion of the cell plate.

Cell Plate:
The cell plate is a structure that forms during cytokinesis in plant cells. It is composed of vesicles containing cell wall material that fuse together to form a continuous membrane-bound compartment. The cell plate expands towards the periphery of the cell, separating the two daughter cells.

Cleavage:
Cleavage is the process of cytokinesis in animal cells. It involves the formation of a contractile ring composed of actin and myosin filaments. This ring contracts and pinches the cell membrane inward, eventually separating the two daughter cells.

Spindle Persistence:
In the given question, the correct answer is option B, which states that the spindle usually persists in the form of a phragmoplast during the cell plate method of cytokinesis. This means that in plant cells, the spindle does not completely disassemble after metaphase but instead reorganizes into a phragmoplast.

During anaphase, the spindle microtubules elongate and push the chromosomes towards the opposite poles of the cell. As the chromosomes reach the poles, the microtubules of the spindle rearrange and form a phragmoplast. The phragmoplast acts as a scaffold for the deposition of new cell wall material, which is transported in vesicles to the equatorial region of the cell.

The vesicles fuse together and fuse with the existing cell membrane, forming a continuous cell plate. The cell plate expands towards the periphery of the cell, eventually fusing with the cell membrane and separating the two daughter cells.

In contrast, during cleavage in animal cells, the spindle microtubules completely disassemble after anaphase, and the contractile ring forms at the equatorial region of the cell. The contractile ring then contracts, pinching the cell membrane inward and separating the two daughter cells.

In summary, the spindle usually persists in the form of a phragmoplast during the cell plate method of cytokinesis in plant cells. This allows for the efficient formation of a new cell wall between the two daughter cells.