Problem 5 - Campbell Biology

Question

In the cells of some organisms, mitosis occurs without cytokinesis. This will result in (A) cells with more than one nucleus. (B) cells that are unusually small. (C) cells lacking nuclei. (D) cell cycles lacking an S phase.

Step-by-Step Solution

Answer

The result is cells with more than one nucleus, so the correct answer is (A).

Step 1: Understand Mitosis and Cytokinesis

Mitosis is the process of nuclear division where one nucleus divides into two, maintaining the chromosome number. Cytokinesis is the process where the cell cytoplasm divides, resulting in two separate daughter cells.

Step 2: Identify the Consequence of Mitosis Without Cytokinesis

In the scenario where mitosis occurs without cytokinesis, the nucleus would divide, but the cell itself would not split into two separate cells.

Step 3: Determine the Result in Terms of Nuclei

Since the cell is not dividing its cytoplasm but the nucleus has divided, the resulting cell will have multiple nuclei within one cell membrane.

Step 4: Select the Correct Answer

Given the information, the correct choice is (A) cells with more than one nucleus.

Key Concepts

Nuclear Division

Nuclear division is the process by which a single nucleus divides into two nuclei. This is done to ensure that each new cell has the same genetic material.
The most common form of nuclear division is mitosis.
During mitosis, a single cell goes through several stages:

• Prophase: Chromosomes condense and become visible.
• Metaphase: Chromosomes align at the cell's equator.
• Anaphase: Sister chromatids are pulled apart to opposite poles of the cell.
• Telophase: New nuclear membranes form around each set of chromosomes.

Nuclear division is crucial for growth, development, and tissue repair.
It ensures that the genetic information is accurately passed on to the daughter cells.

Cytoplasmic Division

Cytoplasmic division, also known as cytokinesis, occurs after nuclear division.
It is the process where the cytoplasm of a parent cell is divided into two daughter cells.
This ensures that each new cell has its own set of organelles and sufficient cytoplasmic material.
Cytokinesis usually starts during the late stages of mitosis:

• A contractile ring made of actin filaments forms around the middle of the cell.
• The ring contracts, pinching the cell into two separate cells.

Without cytokinesis, cells remain as a single entity with multiple nuclei, which can have various implications on cell function and organization.
It is the combination of both nuclear and cytoplasmic division that completes the cell cycle.

Multinucleated Cells

Multinucleated cells are cells that contain more than one nucleus within a single cell membrane.
These cells form when mitosis occurs without cytokinesis.
As discussed, mitosis ensures the distribution of chromosomes, but if the cytoplasm doesn't divide, all nuclei remain within one cell.
Multinucleated cells can be found naturally in some organisms and tissues such as:

• Skeletal muscle cells: These cells are large and require multiple nuclei to manage their extensive cytoplasm.
• Fungal cells: Some fungi naturally have multinucleated cells as part of their life cycle.

In other cases, multinucleated cells can result from a mutation or abnormality in the cell cycle.
Despite their unusual appearance, multinucleated cells function similarly to regular cells but have increased nuclear resources to support a larger cell size.