 Let's learn about cell division. The cell cycle is divided into three major phases. Interphase, mitosis, and cytokinesis. Cells come only from pre-existing cells through the process of cell division. Through mitosis, eukaryotic cells distribute genetic material to daughter nuclei. Cytokinesis divides the cytoplasm and distributes organelles to the two newly formed daughter cells. Each DNA strand was replicated earlier during the S phase of the interphase to form two identical strands called sister chromatids. These chromatids are held together by centromere. The M phase of the cell cycle stands for mitosis or nuclear division. The stages of mitosis are continuous, but for learning purposes, we can divide them into four main phases, prophase, metaphase, anaphase, and telophase. Prophase. During this first phase, the sister chromatids shorten and supercoil, and become visible for the first time during the cell cycle. It is easier to eventually separate sister chromatids in the coiled shortened state than to try and separate long, tangled threads. The nuclear membrane begins to disintegrate. The centrioles replicate and move away from each other due to microtubular action. Metaphase. In this phase, the nuclear membrane has completely disintegrated. Small pieces of membrane stay just under the cell membrane for later use. The spindle fibers reach the centromeres and align the sister chromatids along the center of the cell getting ready for the equal distribution of chromatids to the new cells. Anaphase. The centromeres move apart during this phase and the sister chromatids so that they can be pulled apart by the microtubules. Some spindle fibers shorten and some lengthen, stretching the dividing cell. Telophase. In this last phase, the nuclear membrane reforms around the genetic material. The material then relaxes and stretches out and again becomes visible under the microscope. Mitosis is complete. Animal cells that divide into two actually begin the process of cytoplasmic division during anaphase or telophase by the formation of the contractal ring that eventually separates the daughter cells. If cytokinesis does not follow mitosis, the result is multi-nucleate cells. Plant cells form a cell plate between the two daughter cells and constructing the cellulose-based cell wall. The daughter cells receive molecules and organelles within their cytoplasm. Many tissues contain these cells, called stem cells, which after cytokinesis provide one daughter cell to perform special functions of the tissue while the other daughter cell re-enters the cell cycle to provide new cells as specialized cells die. Both mitosis and apoptosis are genetically programmed to maintain order and balance. You have completed this learning activity on cell division.