Prophase: The first visible stage where chromatin condenses into distinct chromosomes, each consisting of two sister chromatids joined at a centromere. The nuclear envelope breaks down, and the nucleolus disappears as the spindle apparatus begins to form.
Metaphase: Chromosomes migrate to the center of the cell and align along the metaphase plate (equator). Spindle fibers attach to the kinetochores of each centromere, ensuring that each sister chromatid is linked to an opposite pole.
Anaphase: The centromeres divide, and the sister chromatids are pulled apart by the shortening spindle fibers. These separated chromatids, now referred to as individual chromosomes, move toward opposite poles of the cell in a characteristic 'V' shape.
Telophase: Chromosomes reach the poles and begin to decondense back into chromatin. New nuclear envelopes reform around each set of chromosomes, and the spindle fibers disintegrate, resulting in two distinct nuclei within a single cell.
Cell Plate Formation: Unlike animal cells that pinch inward, plant cells possess a rigid cell wall that prevents cleavage. Instead, vesicles from the Golgi apparatus accumulate at the equator and fuse to form a cell plate.
New Cell Wall: The cell plate grows outward until it reaches the existing lateral cell walls, effectively dividing the cytoplasm into two. This plate eventually matures into a new primary cell wall, completing the formation of two independent daughter cells.
| Feature | Plant Mitosis | Animal Mitosis |
|---|---|---|
| Centrioles | Usually absent; spindle forms without them | Present; organize the spindle fibers |
| Cytokinesis | Occurs via cell plate formation | Occurs via cleavage furrow (constriction) |
| Shape Change | Cell maintains rigid rectangular shape | Cell often rounds up during division |
Identifying Stages: When looking at a slide, look for the 'equator' to identify metaphase. If you see two distinct clusters of dark material with a faint line between them, it is telophase or early cytokinesis.
Common Confusion: Do not confuse late anaphase with telophase; in anaphase, the chromosomes are still being actively pulled and often appear pointed toward the poles, whereas in telophase, they begin to clump and lose their distinct 'V' shape.
Calculation Tip: In many exams, you may be asked to calculate the Mitotic Index, which is the ratio of cells undergoing mitosis to the total number of cells observed. Always ensure you count interphase cells in the total count.
