Cytokinesis Splits the Cytoplasm Between Two Daughter CellsCytokinesis is the division of the cytoplasm of a parent cell between the two daughter cells.It gives each daughter cell its own share of organelles, cytoplasm, and a plasma membrane so it can work on its own.Nuclear division separates the genetic material first, then cytokinesis completes the split by dividing the cell body.Cytokinesis usually follows nuclear division rather than happening at the same time.HintCytokinesis is separate from nuclear division.It divides the cytoplasm and its contents, not the genetic material.In Animal Cells, a Cleavage Furrow Pinches the Cell in TwoIn animal cells, cytokinesis is driven by a contractile ring of actin and myosin proteins.This ring forms just beneath the plasma membrane at the cell's equator.Steps of Cytokinesis in Animal CellsFormation of the contractile ringActin and myosin proteins assemble into a ring beneath the plasma membrane.Cleavage furrow formationThe contractile ring tightens and pulls the plasma membrane inward.This creates a cleavage furrow, a groove that deepens as the ring contracts.Pinching the cell apartThe ring keeps constricting until the membrane is pinched into two separate membranes.This splits the cytoplasm and its contents between the two daughter cells.TipPicture the contractile ring as a drawstring on a bag.As the drawstring tightens, the bag closes in on itself and splits into two.Furrow Versus Ring: A Common Mix-UpCommon MistakeDo not confuse the cleavage furrow with the contractile ring.The furrow is the indentation on the cell surface.The ring is the structure beneath the membrane that makes the furrow form.In Plant Cells, a Cell Plate Builds a New WallA plant cell has a rigid cell wall, so it cannot simply pinch inward.Instead, the cell builds a new cell wall and plasma membrane between the two daughter cells.Steps of Cytokinesis in Plant CellsFormation of the cell plateVesicles from the Golgi apparatus carry cell wall materials such as pectins and cellulose to the cell's equator.These vesicles line up and fuse to form a cell plate.Expansion of the cell plateThe cell plate grows outward as more vesicles fuse, until it reaches the existing plasma membrane.Formation of the middle lamella and cell wallThe fused vesicles form two membranes, which become the plasma membranes of the daughter cells.Pectins are laid down between these membranes to form the middle lamella, which glues the two cells together.Each daughter cell then builds its own cell wall by laying down cellulose next to the middle lamella.AnalogyPicture a crew building a wall to split a room in two.The vesicles are the delivery trucks bringing materials to the site.The cell plate is the frame that grows into a solid wall.The Cell Plate Is Only a ScaffoldNoteThe cell plate is not a permanent structure.It acts as a scaffold for the new cell wall and plasma membranes.Cytokinesis Gives Each Daughter Cell a Complete, Working CopyCytokinesis makes sure each daughter cell gets a complete set of organelles and cytoplasm.Without it, nuclear division would leave a single cell with many nuclei, which disrupts normal cell function.Theory of KnowledgeHow do the structural differences between animal and plant cells shape their methods of cytokinesis?What does this reveal about the link between form and function in biology?Check Your UnderstandingActive recallDefine cytokinesis in one sentence.What structure drives cytokinesis in animal cells, and what visible feature does it create?How does a cell plate form in a plant cell, and where do its materials come from?Why do animal and plant cells divide their cytoplasm in different ways?What would happen to a cell if nuclear division occurred but cytokinesis did not?
