The cleavage furrow is the indentation in the cell membrane of an animal cell where a ring of microfilaments contracts to pinch the cytoplasm in two during cytokinesis, the final step of cell division.
The cleavage furrow is the first physical sign that an animal cell is splitting its cytoplasm. Picture pulling a drawstring tight around the middle of a water balloon. A ring of protein filaments (made of actin and myosin, the same stuff in your muscles) tightens just under the cell membrane and squeezes inward, creating a shallow groove. That groove is the cleavage furrow. As the ring keeps contracting, the furrow deepens until the cell pinches all the way through into two separate daughter cells.
This happens during cytokinesis, which is the division of the cytoplasm that follows mitosis. By the time the furrow forms, the DNA has already been copied and separated, so each new cell ends up with a full set of chromosomes. The cleavage furrow is the animal-cell version of this pinching step. Plant cells don't pinch this way because their rigid cell walls won't let them, so they build a cell plate down the middle instead.
The cleavage furrow lives in Unit 4: Cell Communication and Cell Cycle, under topic 4.6 Regulation of the Cell Cycle. It's the visible payoff at the very end of the whole cell cycle process described in AP Bio 4.6.A, where checkpoints and cyclin-CdK interactions control whether a cell is even allowed to divide. The furrow is what division physically looks like once those internal controls give the green light. Understanding it helps you connect the abstract checkpoint regulation to the concrete event of one cell becoming two, which is the kind of cause-and-effect reasoning the AP exam rewards.
Keep studying AP Biology Unit 4
Cytokinesis (Unit 4)
The cleavage furrow IS the mechanism of cytokinesis in animal cells. Cytokinesis is the big-picture step of splitting the cytoplasm, and the furrow is the specific tool an animal cell uses to get it done.
Cell Plate (Unit 4)
Plant cells can't pinch inward because of their cell walls, so instead of forming a furrow they build a cell plate down the middle. Same goal of two daughter cells, opposite strategy, and a classic compare-and-contrast on the exam.
Mitosis (Unit 4)
Mitosis separates the duplicated chromosomes, and the cleavage furrow finishes the job by separating the cytoplasm. Mitosis comes first, the furrow comes last, so don't lump them together.
Regulation of the Cell Cycle (Unit 4)
Checkpoints and cyclin-CdK activity (AP Bio 4.6.A) decide whether a cell advances toward division at all. If those controls fail or get blocked, the cell never reaches the point of forming a furrow.
You won't see a whole FRQ devoted to the cleavage furrow itself, but it shows up as the recognizable endpoint of division in cell-cycle questions. Expect MCQ stems that test whether you know furrow formation belongs to cytokinesis in animal cells, and that plant cells use a cell plate instead. The bigger exam skill is reasoning about disruptions. For example, a question might describe a chemotherapy drug that stabilizes microtubules so they can't shorten, then ask for the immediate effect on a dividing cell. You'd reason that chromosomes can't be pulled apart, so the cell stalls before it ever gets to forming a furrow. Similar logic applies to questions about blocking cyclins, which halts cells well before division even begins (AP Bio 4.6.A and 4.6.B).
Both finish cell division, but the cleavage furrow is the animal-cell move and the cell plate is the plant-cell move. The furrow pinches inward from the outside, while the cell plate builds outward from the center. If the question mentions a cell wall, you want the cell plate, not the furrow.
The cleavage furrow is the groove in an animal cell's membrane where a contracting ring of microfilaments pinches the cytoplasm into two daughter cells.
It happens during cytokinesis, the final step of cell division, after mitosis has already separated the chromosomes.
Animal cells use a cleavage furrow; plant cells use a cell plate because their cell walls can't be pinched.
Furrow formation only happens if checkpoints and cyclin-CdK activity have allowed the cell cycle to proceed (AP Bio 4.6.A).
Disrupting earlier steps, like blocking microtubules or cyclins, stalls the cell before it ever reaches the furrow stage (AP Bio 4.6.B).
It's the indentation in an animal cell's membrane where a ring of actin and myosin filaments contracts to pinch the cell in two. It's the first visible sign of cytokinesis at the end of cell division.
No. Cytokinesis is the whole process of dividing the cytoplasm, and the cleavage furrow is the specific structure animal cells use to carry it out. The furrow is the mechanism; cytokinesis is the event.
A cleavage furrow pinches an animal cell inward from the membrane, while a cell plate forms outward from the center in plant cells. Plants can't use a furrow because their rigid cell walls won't let the cell squeeze inward.
No. Plant cells divide using a cell plate that grows across the middle of the cell and becomes a new cell wall. Only animal cells (and other cells without rigid walls) form a cleavage furrow.
It forms at the very end, during cytokinesis, right after mitosis has separated the chromosomes. The cell only gets there if cell-cycle checkpoints and cyclin-CdK activity allowed it to advance (AP Bio 4.6.A).
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