Which term refers to the pinching of the cell membrane in animal cells during cytokinesis?

• A. Cleavage furrow
• B. Cell plate
• C. Nucleolus
• D. Spindle

Answer: (A)

During cytokinesis in animal cells, a contractile ring of actin filaments sits just beneath the plasma membrane at the cell’s equator. Its tightening pulls the membrane inward, creating a shallow groove called the cleavage furrow. As constriction continues, the furrow deepens until the cell splits into two daughter cells. Plant cells don’t form a cleavage furrow because their rigid cell wall prevents inward pinching; instead, vesicles coalesce to build a cell plate that eventually separates the cells. The nucleolus is a nuclear structure involved in ribosome production, and the spindle is the mitotic apparatus that helps separate chromosomes during mitosis, not the membrane pinching seen in animal cytokinesis.