Which structure is involved in the formation of the spindle apparatus during mitosis?

The structure that is involved in the formation of the spindle apparatus during mitosis is the centrioles. Centrioles are cylindrical organelles located in the cell's centrosome and play a crucial role in organizing microtubules into the spindle fibers that are essential for separating chromosomes during cell division. During mitosis, the centrioles replicate and move to opposite poles of the cell, from where they help to anchor and organize the spindle apparatus.

The spindle apparatus itself is made up primarily of microtubules, which elongate and attach to the kinetochores of the chromosomes, ensuring that the sister chromatids are pulled apart properly during anaphase. This process is critical for ensuring that each daughter cell receives an exact copy of the genetic material.

While other structures mentioned in the options have important roles within the cell, they do not directly contribute to the formation of the spindle apparatus. For instance, the nuclear membrane is involved in enclosing the nucleus and dissolves during mitosis, yet it does not contribute to spindle formation. Chromatids are the duplicated forms of chromosomes that are separated during cell division and, while important, they are the ones being moved rather than forming the apparatus. Chromatin is the less condensed form of genetic material