Cytokinesis is the final stage of cell division, involving the division of a parent cell’s cytoplasm into two distinct daughter cells. This process ensures each new cell receives a complete and equitable share of organelles and cellular components, allowing them to function independently and correctly.
Animal Cell Cytokinesis
In animal cells, cytokinesis begins shortly after anaphase and concludes during telophase. The first visible sign is the formation of a “cleavage furrow,” an indentation on the cell’s surface. This furrow forms around the cell’s equator, marking the future division plane.
The formation and deepening of the cleavage furrow are driven by the contractile ring, a specialized structure located beneath the plasma membrane. This ring is primarily composed of actin filaments and myosin II filaments. Similar to muscle contraction, these filaments interact and slide past each other, causing the ring to constrict. This constriction progressively pinches the cell membrane inward, dividing the parent cell into two daughter cells. This inward progression from the periphery is described as centripetal.
Plant Cell Cytokinesis
Plant cell cytokinesis proceeds through a mechanism distinct from animal cells. A rigid cell wall surrounding plant cells prevents cleavage furrow formation, as the wall cannot be easily pinched inward. Instead, plant cells construct a new cell wall, called the cell plate, in the middle of the dividing cell.
The development of the cell plate begins with vesicles, largely derived from the Golgi apparatus, which transport cell wall materials like polysaccharides and glycoproteins. These vesicles are guided to the equatorial plane of the cell by the phragmoplast, an assembly of microtubules. The vesicles then fuse at the cell’s center, forming a nascent cell plate.
As more vesicles arrive and fuse, the cell plate expands outwards from the center of the cell towards the existing parent cell walls. This outward growth continues until the cell plate fuses with the original cell wall, creating a complete new cell wall and plasma membrane that separates the two daughter cells. This process, where division progresses from the center outwards, is described as centrifugal.
Fundamental Differences in Process
The differing mechanisms of cytokinesis in plant and animal cells stem from their fundamental structural compositions. Animal cells lack a rigid outer cell wall, possessing only a flexible plasma membrane. This allows them to physically pinch in two through the constriction of a contractile ring. The inward “pinching” action, facilitated by the actin and myosin filaments, effectively cleaves the cytoplasm.
In contrast, plant cells are encased by a rigid cell wall. This structure prevents cleavage furrow formation and the pinching mechanism seen in animal cells. Consequently, plant cells must build a new barrier from the inside out. They achieve this by assembling a cell plate from Golgi-derived vesicles, which matures into a new cell wall that divides the two daughter cells. The distinct structures involved—the contractile ring in animal cells and the cell plate guided by the phragmoplast in plant cells—highlight these divergent evolutionary adaptations for cytoplasmic division.