Problem 142 - Objective Biology for NEET

Question

Assertion: Cell growth results into division. Reason: Cell growth leads to change in nucleocytoplasmic ratio.

Step-by-Step Solution

Answer

The assertion 'Cell growth results into division' is correct, and the reason 'Cell growth leads to change in nucleocytoplasmic ratio' is also correct, and it is the accurate explanation for the assertion. So, both the assertion and the reason are correct, and the reason is a correct explanation for the assertion.

Step 1: Understanding Cell Growth

Cell growth is a vital process where a cell increases in size. It is an important part of the cell cycle that leads to cell division.

Step 2: Understanding Cell Division

Cell division is a process by which a parent cell divides into two or more daughter cells. It is a method for growth and, in multicellular organisms, for replacement of old cells.

Step 3: Understanding Nucleocytoplasmic Ratio

The nucleocytoplasmic ratio is the ratio of the volume of the nucleus to the volume of the cytoplasm in a cell. As a cell grows, this ratio changes. Initially, when a cell is small, the ratio is high. But as the cell grows, the ratio reduces because although the cytoplasm volume increases, the nuclear volume remains relatively constant.

Step 4: Interconnection Between Cell Growth and Division

As the cytoplasm grows more quickly than the nucleus, the nucleocytoplasmic ratio decreases. Once the ratio reaches a certain lower limit, cell division is triggered to restore the ratio and ensure efficient cell functioning. Hence, the change in nucleocytoplasmic ratio as a result of cell growth does lead to cell division.

Key Concepts

Cell Growth

Cell growth is a fundamental process during which a cell increases in size. This expansion is essential for subsequent cell division, allowing organisms to grow and repair tissues. In the context of the cell cycle, growth occurs in the preparation stages before division, specifically during the G1 phase. Here, cells synthesize proteins, produce more organelles, and increase in volume.

During this time:

• The cell expands its metabolic capacity.
• It ensures it has the necessary materials for DNA replication.
• Energy and resources are invested to prepare for splitting into two new cells.

Thus, the end-goal of cell growth is to equip the cell with adequate size and resources necessary for successful cell division.

Nucleocytoplasmic Ratio

The nucleocytoplasmic ratio is a key factor in understanding cell growth and division. It represents the balance between the volumes of a cell's nucleus and its cytoplasm. Initially, a cell has a high nucleocytoplasmic ratio, indicating a small cytoplasm relative to its nucleus.

As the cell grows:

• The cytoplasm's volume increases significantly.
• Meanwhile, the nucleus maintains a relatively stable size.
• This causes the nucleocytoplasmic ratio to decrease.

This ratio is critical because it influences cell function and efficiency. When it drops to a specific threshold, it signals the cell to divide, balancing the nuclear and cytoplasmic volumes across two new cells.

Cell Cycle

The cell cycle is a series of stages that a cell passes through to divide and replicate. It comprises distinct phases that ensure orderly growth and division, maintaining proper function in organisms. These phases include:

• G1 (Gap 1) Phase: The cell grows and prepares the necessary building blocks for DNA synthesis.
• S (Synthesis) Phase: The cell duplicates its DNA so that each new cell will have a complete set of genetic material.
• G2 (Gap 2) Phase: Further growth occurs, and the cell makes final preparations for division.
• M (Mitosis) Phase: This is where actual cell division takes place, resulting in two daughter cells.

Throughout the cycle, checkpoints exist to ensure that processes have been completed accurately, preventing errors in cell division. Mastery of this cycle is crucial for understanding how organisms grow, maintain, and repair themselves.