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|Chapter Five: Cell Reproduction|
Cytokinesis is the final stage of cell reproduction; it is the division of the cytoplasm into approximately equal halves, resulting in a roughly equal distribution of organelles in each of the daughter cells. Cytokinesis usually begins in telophase. We will discuss cytokinesis separately for organisms which do not have a cell wall (mostly heterotrophs) and those which do have a cell wall (generally autotrophs).
For a cell without a cell wall, cytokinesis begins with the pinching inward of the cell membrane caused by the action of a ring of special contractile proteins called actin and myosin. The pinching inward forms a deep grove, often called the cleavage furrow. Eventually, the opposite sides of the furrow meet and the cell splits into two new daughter cells.
Whereas cytokinesis in cells lacking a cell wall occurs through a pinching inward, organisms with a cell wall undergo a process through which a so-called cell plate is built from the middle of the cell outward to the membrane. Vesicles from the Golgi bodies flatten and fuse in the center of the cell, forming the cell plate, which elongates toward the cell membrane as more vesicle are added. When the cell plate reaches the cell membrane, the parent cell is effectively separated into two new daughter cells, which then proceed to build a cell wall along the cell plate.