Cytokinesis: Division of Cytoplasm in Cell Division

Cytokinesis is the division of the cytoplasm that follows nuclear division. It separates one cell into two complete daughter cells, each with its own nucleus and share of organelles. Without cytokinesis, a cell would end up with two nuclei in one body.

Cytokinesis matters because it completes cell division for growth and repair. Its method differs between animal and plant cells, and that difference is a favourite exam topic and a clue to how cell walls shape plant life.

Key Concepts

In animal cells, cytokinesis occurs by a cleavage furrow: a contractile ring of actin and myosin filaments pinches the cell membrane inward until the cell splits. In plant cells, a rigid wall prevents pinching, so a cell plate forms in the centre from vesicles supplied by the Golgi apparatus. The cell plate grows outward and becomes the new wall, called the middle lamella first. Cytokinesis usually begins during late anaphase or telophase and overlaps with the end of mitosis.

How It Works

1. The spindle signals the position where division should occur, usually the cell equator.
2. Animal cells form a contractile ring that tightens like a drawstring.
3. Plant cells deliver wall-building vesicles to the equator.
4. The furrow deepens or the cell plate expands until two cells separate.
5. Each daughter cell receives cytoplasm, organelles and a nucleus.

Worked Example

A parent plant cell is 40 micrometres wide. The cell plate begins at the centre and grows toward both sides. Distance to cover on each side = 40 ÷ 2 = 20 micrometres. If vesicles add plate material at 2 micrometres per minute on each side, time to reach the wall = 20 ÷ 2 = 10 minutes. After about 10 minutes the plate meets the parent wall and two daughter cells are formed.

Common Misconceptions

• Students think cytokinesis and mitosis are the same. Mitosis divides the nucleus; cytokinesis divides the cytoplasm.
• Many believe plant cells form a cleavage furrow. The stiff cell wall prevents pinching, so plants build a cell plate instead.
• Some assume cytoplasm divides exactly equally always. Organelle distribution can be uneven, though both daughters receive enough to survive.

Real-World Applications

Researchers studying cell-plate formation aim to improve crop growth and wood formation. In medicine, abnormal cytokinesis producing multinucleate cells is observed in some cancers. Tissue engineers control cell division to grow skin sheets for burn treatment.

Cytokinesis finishes cell division by splitting the cytoplasm, through a furrow in animal cells and a cell plate in plant cells. It ensures each new nucleus becomes a complete, independent cell.