Which structure creates the cleavage that splits an animal cell into two during cytokinesis?

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

Answer: (B)

During cytokinesis in animal cells, a contractile ring of actin filaments forms a belt just under the plasma membrane. As this ring contracts, it pulls the membrane inward, creating a cleavage furrow that deepens until the membrane fuses and the cytoplasm is divided, producing two separate daughter cells. This mechanism is specific to animal cells; plant cells don’t form a cleavage furrow because their rigid cell walls require vesicles to coalesce at the center to build a separating cell plate that eventually becomes the cell wall. The spindle apparatus, while essential for organizing and separating chromosomes during mitosis, isn’t the structure that physically splits the cell membrane. The nucleolus is involved in ribosome production inside the nucleus and has no role in cytokinesis.