Advanced Placement (AP) Biology Practice Exam

What is the term for the first sign of cleavage in an animal cell?

1. Cleavage furrow

2. Centrosome

3. Metaphase plate

4. Spindle apparatus

The correct answer is: Cleavage furrow

The term for the first sign of cleavage in an animal cell is the cleavage furrow. During the process of cytokinesis, which separates the cytoplasm of a parental cell into two daughter cells, the cleavage furrow is formed as the cell membrane begins to constrict in the middle of the cell. This constriction is driven by a contractile ring composed of actin and myosin filaments, which pinch the cell membrane inward. As the contractile ring tightens, it creates a visual indentation on the surface of the cell that appears as a furrow. The cleavage furrow deepens progressively until the cell is pinched in two, resulting in the formation of two separate daughter cells. This process is characteristic of animal cells, as they lack the rigid cell wall found in plant cells, which instead form a cell plate during division. In contrast, the centrosome is the organelle that serves as the main microtubule organizing center, while the metaphase plate refers to the plane where chromosomes align during metaphase of cell division. The spindle apparatus is the complex of microtubules that orchestrates the movement of chromosomes during cell division. None of these terms represents the initial physical sign of cell division like the cleavage furrow does