As a cell begins the process of dividing, its chromosomes become shorter, thicker, and individually visible in an LM (light micrograph). Explain what is happening at the molecular level.

Cell division is the process of replication of cells by dividing the DNA along with the other contents of the cells. There are two types of cell division, which are mitosis and meiosis. The mitosis process takes place in the normal cells, and meiosis occurs in the sex cells.

The thread-like structure present within the nucleus is the chromosomes. The structural composition of the chromosome consists of DNA along with the protein. These proteins are called histones.

The DNA protein complex is the chromatin. There are two types of chromatins such as heterochromatin and euchromatin. The chromatin that is lightly packed is the euchromatin. The chromatin that is tightly packed and denser in appearance is the heterochromatin.

In the nucleus, the DNA is found indiscrete arrangements. This arrangement of structure is the chromosomes. It is made of long strands of DNA associated with protein. It makes a complex called chromatin. This chromatin condenses the chromosomes by coiling up.

During normal time, like in the absence of cell division, the chromatin does not condense, and the chromosome appears to be lengthier. So, the appearance of chromatin pretends to be like a diffused mass in micrographs when it is viewed under a light microscope. This distinct image of the chromosome is not visible at this normal time.

Hence, at the time of cell division, the chromosomes condense due to the coiling of the chromatin. So, it is visible as a separate structure while viewing under a light microscope.