Advanced Placement (AP) Biology Practice Exam

What is the primary purpose of cytokinesis?

1. Replication of DNA

2. Division of the cytoplasm

3. Preparation for mitosis

4. Assembly of the spindle apparatus

The correct answer is: Division of the cytoplasm

The primary purpose of cytokinesis is the division of the cytoplasm, which occurs after mitosis in the cell cycle. During cytokinesis, the cytoplasmic contents of a parent cell are separated into two daughter cells. This process ensures that each daughter cell receives an adequate amount of organelles, proteins, and cellular materials necessary for their function and survival. Cytokinesis typically follows the segregation of chromosomes that occurs during mitosis, marking the end of the cellular division process. It is crucial because, without proper cytokinesis, daughter cells might end up with an incomplete set of cellular components or might not separate at all, leading to cells that either cannot function properly or become multinucleated. This process can vary between plant and animal cells. In animal cells, a cleavage furrow forms, which pinches the cell into two. In plant cells, a cell plate forms down the center of the cell, eventually leading to the formation of a new cell wall that separates the two daughter cells. Both methods highlight that the essential role of cytokinesis is to ensure that the cytoplasm and its contents are evenly distributed among the new cells.