Question

Describe and compare the process of cytokinesis in animal cells and in plant cells.

Short answer

Cytokinesis is the process of dividing a single eukaryotic cell into two separate cells during cell division. In animal cells, cytokinesis involves the formation of a cleavage furrow using a contractile ring made of actin and myosin proteins. The membrane is then pinched into two separate cells, creating two daughter cells. In plant cells, cytokinesis occurs differently due to their rigid cell wall, using a cell plate formation through phragmoplasty. The cell plate is formed by the fusion of vesicles containing cell wall materials, and it eventually fuses with the existing cell wall, forming a new cell wall between the two daughter cells.

Step-by-step solution

Overview of Cytokinesis

Cytokinesis is the process by which the cytoplasm of a single eukaryotic cell is divided into two separate cells during cell division. This occurs after nuclear division (mitosis or meiosis) has taken place. The process may be different in animal and plant cells due to their structural differences.

Differences in Structure of Animal and Plant Cells

Before we discuss the process of cytokinesis, it is essential to understand the differences in the structure of animal and plant cells. Animal cells have a flexible cell membrane while plant cells have a rigid cell wall made up of cellulose. Animal cells change their shape during cytokinesis, whereas plant cells face difficulty due to their rigidity.

Cytokinesis in Animal Cells

In animal cells, cytokinesis involves the formation of a cleavage furrow. This process begins at the cell's equator, where a contractile ring made of actin and myosin proteins forms beneath the plasma membrane. The contractile ring starts to contract, pulling the membrane with it, creating an inward furrow. As the furrow deepens and the contractile ring continues to contract, the cell is pinched into two separate cells. Finally, cell membrane fusion occurs at the midpoint, creating two daughter cells.

Cytokinesis in Plant Cells

In plant cells, cytokinesis occurs differently due to the presence of a rigid cell wall. Instead of a cleavage furrow, plant cells form the cell plate through a process called phragmoplasty. Vesicles containing cell wall materials, originating from the Golgi apparatus, gather at the metaphase plate. These vesicles fuse, forming a flattened, disc-like structure called the cell plate. As more vesicles join and fuse, the cell plate grows outward, eventually fusing with the existing cell wall. Finally, a new cell wall is formed between the two daughter cells, completing the process of cytokinesis.

Comparing Cytokinesis in Animal and Plant Cells

Both animal and plant cells undergo cytokinesis to divide the cytoplasm and create two separate cells. While animal cells use the contractile ring mechanism to form a cleavage furrow and pinch the cells apart, plant cells employ a cell plate formation to construct a new cell wall between the two daughter cells. The differences in cytokinesis processes are primarily due to the differences in their structural components – a flexible cell membrane in animal cells and a rigid cell wall in plant cells. Overall, cytokinesis in animal and plant cells is an essential process for cell division. The primary difference lies in the method employed, cleavage furrow in animal cells, and cell plate formation in plant cells, due to their structural differences. The end goal, however, remains the same – to create two separate and functional daughter cells.

Key concepts

Cell Division

Cell division is a fundamental process that occurs in all living organisms to reproduce and repair tissue. In eukaryotic cells, it involves two major steps: nuclear division (mitosis or meiosis) and cytokinesis. Mitosis is responsible for the equal distribution of replicated chromosomes into two new nuclei, while cytokinesis divides the cell's cytoplasm, resulting in two separate daughter cells. This division is crucial for growth, development, and maintenance of multicellular organisms.

Cytokinesis in eukaryotic cells must be precisely timed to ensure that each daughter cell receives the correct amount of cytoplasm and organelles. Errors in the process can lead to cells with abnormal numbers of chromosomes or insufficient cellular components, which can disrupt normal growth and function, potentially leading to disease.

Cleavage Furrow

In animal cells, cytokinesis is facilitated by the formation of a cleavage furrow. This indentation marks the start of the cell physically dividing into two. The proteins actin and myosin, known for their role in muscle contraction, are also central to this process. They form a contractile ring along the equator of the cell, beneath the plasma membrane.

As the ring contracts, it pulls the cell membrane inward, creating the furrow and eventually pinching the cell in two. This process resembles the tightening of a drawstring bag, where gradually drawing the strings closes the bag's mouth. The cleavage furrow is a dynamic structure, its formation and deepening elegantly coordinated by molecular signals and cellular architecture.

Cell Plate Formation

In stark contrast to animal cells, plant cells form a cell plate during cytokinesis, a process tailored to accommodate the rigid cell wall. The cell plate arises at the metaphase plate, the site where chromosomes line up during mitosis. Vesicles from the Golgi apparatus, filled with components necessary for building a cell wall, are transported to the middle of the cell.

These vesicles fuse, forming a membranous disc that eventually expands outwards and integrates with the existing cell walls. This results in the formation of two distinct chambers, each housing a new daughter cell. The seamless execution of cell plate formation is vital for maintaining the integrity of the plant tissue and ensuring that each new cell is properly encased in a protective wall.

Phragmoplasty

The term phragmoplasty refers to the intricate process that underpins cell plate formation in plant cells. It begins with the establishment of a phragmoplast, a complex structure composed of microtubules, actin filaments, and other proteins. It serves as a scaffold for the vesicles that coalesce to form the initial cell plate.

In this microtubule-rich region, vesicles are guided to the center, where they bring the building blocks of the cell wall. As more vesicles join this assembly, the cell plate enlarges until it meets and fuses with the parental cell wall. This stage marks the completion of cytokinesis in plant cells, showcasing the phragmoplast's crucial role in ensuring a successful and ordered division.