Hello. You did not present the image to which this question refers, which makes it impossible for this question to be answered. However, I will try to help you in the best possible way.
I believe you are looking at cells from the tip of the root, in an experiment where the tip of the root of the onion was cut. To redo the tip of the root, the onion cells will undergo mitosis, which is the cell division where a cell originates from two identical cells.
Mitosis has five phases and all of them can be seen in the onion root cells according to the following characteristics:
1. Interphase: it is the moment when the cells increase in size and intensify their metabolic activity. The cells of the onion root will be in this phase when they appear as a completely dark and filled circle.
2. Prophase: The chromosomes condense and become visible and the cell membrane is flawed. In the cells of the onion root, you will be able to see this phase in cells that appear as an irregular circle, with a tangle of lines scattered inside.
3. Metaphase: The chromosomes condense further and connect to the spindle lines that are in the center of the cell. In the onion root cells, you will identify this phase in circles with a tangle of lines that are concentrated in the center of the cells.
4. Anaphase: The centromeres are separated and the sister chromatids migrate to the poles of the cell. You will be able to see this phase in cells that have a concentration of lines at both ends of the cell.
5. Telophase: the chromosomes are decondensed and the cell membrane is formed again while the cell separates into two. You will see this phase with the presentation of two cells.
To improve your understanding, the attached figure below shows how the cell appears in each phase.