Question

Animal cells undergo cytokinesis by (a) Furrowing (b) Cell plate (c) Both (a) and (b) (d) Furrowing and followed by the deposition of special materials

Short answer

The correct answer to how animal cells undergo cytokinesis is (a) Furrowing.

Step-by-step solution

Understand the Question

Cytokinesis is the process where a single cell divides into two. The question asks how this process takes place in animal cells. The choices provided are: furrowing, cell plate, both furrowing and cell plate, and furrowing followed by the deposition of special materials.

Understanding Furrowing

Furrowing, also known as cleavage, is the process where a contractile ring of actin and myosin (protein filaments) forms a furrow around the middle of the cell, tightening and deepening it until the cell is pinched in two, forming two separate cells. This is the process that occurs in animal cells.

Considering Other Choices

Cell plate formation occurs in plant cells, not animal cells, during cytokinesis. So, the options involving cell plate (choices (b) and (c)) can be ruled out. The deposition of special materials after furrowing is not a step that occurs in the cytokinesis of animal cells, so option (d) can be ruled out as well.

Concluding the Answer

Based on the process of cytokinesis in animal cells, the correct answer is Furrowing (option (a)). This is because in animal cells, cytokinesis occurs by the formation of a cleavage furrow, which eventually divides the cell into two daughter cells

Key concepts

Furrowing

In the world of cell biology, furrowing is a critical process during the cytokinesis phase of cell division in animal cells. It’s like the cell cinching its belt to create two separate entities from one. Imagine a balloon pinched in the center to form two smaller balloons; this is furrowing in a nutshell. During this stage, actin and myosin, two types of protein filaments, work together to form a constriction belt around the midsection of the cell. This belt, or ring, tightens progressively, much like pulling a drawstring bag closed, which indents the cell membrane and forms a furrow around the equator of the cell.

The furrowing process is driven by the contractile ring's tension, which pulls the cell membrane into the center, deepening the furrow until the cell is snuggly pinched in two. This gives rise to two separate but genetically identical daughter cells. Each inherits a full set of chromosomes and a portion of the parent cell's cytoplasm. Furrowing ensures that each daughter cell is ready to start its own life cycle, having received all the necessary cellular components for survival and function.

Contractile Ring Formation

Contractile ring formation is a fascinating ballet of tiny filaments coming together in precise choreography. It's the prelude to the final act of cell division where the curtain comes down, splitting one cell into two. The ring, composed of actin and myosin proteins, encircles the cell like a miniature muscle. Actin acts as the scaffold, while myosin serves as the motor, using energy from ATP to slide along the actin filaments.

These two proteins cooperate to generate force, pulling the ring tighter and tighter. This happens in subcellular whispers, nearly imperceptibly, as the ring constricts—converging towards the center of the cell. It's essential in creating the cleavage furrow and eventually severing the cell’s connection, allowing for a successful cytokinesis. This process is akin to a drawstring bag being pulled closed, however, on a much smaller scale, involving intricate activities of microscopic structures.

Cleavage Furrow

The cleavage furrow is the visible indentation that signifies the beginning of the end of a cell’s current form as it embarks on producing two daughter cells. Crudely put, it's as if the cell begins to form a 'waist'. This furrow appears due to the tension applied by the contractile ring and is the first sign that cytokinesis is underway.

It is essential to understand that the cleavage furrow is not just a surface feature. It involves a complex interplay of cytoskeletal components beneath the cell membrane. As the contractile ring tightens, it pulls the cytoskeleton and the cell membrane along with it, forging a deeper and deeper indentation until the original cell is cleaved into two new ones. The precision of this process is vital for ensuring that the resulting daughter cells are healthy and equipped to progress through their own life cycles.

Cell Division in Eukaryotes

Cell division in eukaryotes is an orderly and meticulously regulated event, encompassing two major processes: mitosis and cytokinesis. While mitosis deals with the copying and separation of genetic material, cytokinesis is the physical splitting of the cell's cytoplasm, resulting in two separate and complete cells. In animal cells, cytokinesis is characterized by the aforementioned cleavage furrow method.

In contrast, plants and other rigid-walled organisms employ a different mechanism involving the formation of a cell plate. In animal cells, this stage of cell division is fascinating as it uses pre-existing structures like microtubules from the cell's cytoskeleton to ensure that the newly formed cells are endowed with the correct components and organelles. Proper cell division is paramount as errors in this process can lead to cell malfunction or diseases such as cancer.