A scientist examining a stained slide of an onion root tip identifies two cells at different stages of mitosis.
Cell 1: Chromosomes are visible as distinct structures, each consisting of two sister chromatids. They are arranged in a single plane at the centre of the cell. Spindle fibres are clearly visible extending from the poles to the centromeres. No nuclear envelope is present.
Cell 2: Chromosomes are grouped at opposite poles of the cell. A new nuclear envelope is forming around each chromosome cluster. A cell plate is beginning to develop in the middle of the cell. Spindle fibres are no longer visible.
Explain the differences in chromosome behaviour and the state of the nuclear envelope and spindle between these two cells. In your answer, name the mitotic stage for each cell.