Cytokinesis
Cytokinesis is the final stage of cell division in both mitosis and meiosis, following karyokinesis in which the nucleus divides. The primary goal of cytokinesis is to partition the cytoplasm and associated organelles into two distinct daughter cells. This process varies significantly between animal and plant cells.
In animal cells, cytokinesis begins with the formation of a cleavage furrow that encircles the cell and gradually deepens, resulting in the division of cytoplasmic contents. This furrow is facilitated by a structure called the contractile ring, composed primarily of actin filaments, which constricts as the furrow deepens. The cleavage furrow eventually meets at the center, hence achieving the complete separation of the two daughter cells.
Conversely, in plant cells, cytokinesis is distinct due to the presence of a rigid cell wall. Instead of forming a furrow, plant cells develop a cell plate at the center of the cell where vesicles containing cell wall materials fuse. This cell plate expands outward and eventually fuses with the existing cell wall, creating two separate daughter cells. Organelles such as mitochondria and plastids are also distributed between the daughter cells during this process.
In some cases, cytokinesis may not follow karyokinesis, particularly in certain fungi and animal cells, resulting in multinucleate cells known as syncytia. An example of this phenomenon is found in the liquid endosperm of coconuts. Understanding cytokinesis is crucial as it completes the cell division process, ensuring that each daughter cell maintains its genetic material and cell structure.