Problem 58 - Objective Biology for NEET

Question

Mitosis is (a) Karyokinesis (b) Cytokinesis (c) Reduction in chromosome number (d) Both (a) and (b)

Step-by-Step Solution

Answer

The correct answer is (d) Both (a) and (b).

Step 1: Understand the Terms

Learn and understand the definitions of Karyokinesis, Cytokinesis and reduction in chromosome number. Karyokinesis refers to the division of the nucleus during mitosis. Cytokinesis refers to the division of the cytoplasm, completing the process of cell division. When a cell undergoes a process that decreases the chromosome number, it's referred to as a reduction in chromosome number.

Step 2: Identify which processes belong to Mitosis

Now that you know what each term means, you can easily identify which processes belong to Mitosis. Here, both Karyokinesis and Cytokinesis belong to Mitosis, as they stand for nucleus and cytoplasm division respectively, both of which occur during Mitosis.

Step 3: Match with given options

Find the option that mentions both Karyokinesis and Cytokinesis as part of Mitosis. In the given options, choice (d) mentions both (a) and (b) i.e., Karyokinesis and Cytokinesis, which are indeed components of Mitosis. Hence, the right answer is (d) Both (a) and (b).

Key Concepts

Karyokinesis

Karyokinesis is the process during cell division where the nucleus of the cell divides. This is a primary stage of mitosis and ensures that the genetic material is evenly distributed to the daughter cells. During karyokinesis, the chromatin in the nucleus condenses into chromosomes, which are then correctly aligned along the metaphase plate.
Following this, the chromosomes are pulled apart by the spindle fibers and move to opposite poles of the cell. This ensures that each new cell receives an identical set of chromosomes.
Karyokinesis can be broken down into further stages:

• Prophase: Chromosomes become visible, and the mitotic spindle forms.
• Metaphase: Chromosomes align at the cell's equator.
• Anaphase: Sister chromatids separate to each pole.
• Telophase: Chromatids arrive at poles, and nuclear membranes start re-forming.

This intricate process ensures the accurate separation of genetic material, thereby ensuring genetic stability across cell generations.

Cytokinesis

Following karyokinesis, cytokinesis is the division of the cytoplasm, the cell's content outside the nucleus. This ensures that the two new daughter cells are completely separate and have their own complete set of cellular machinery.
In animal cells, this process involves the formation of a cleavage furrow, which pinches the cell into two distinct cells. This occurs through the contraction of actin and myosin filaments just beneath the cell membrane.
In contrast, plant cells construct a cell plate that eventually matures into a separating cell wall. This difference is due to the rigid cell walls in plants which prevents the formation of a furrow.

• In Animals: Formation of a cleavage furrow.
• In Plants: Formation of a cell plate.

Cytokinesis is essential as it completes the process of cell division, ensuring each daughter cell has the components necessary to survive and function.

Cell Division

Cell division is the overarching process by which cells duplicate their contents and divide to form new cells. This cycle of growth and division is vital for growth, repair, and reproduction in organisms. The entire cell division process consists of two main parts: karyokinesis and cytokinesis.
Mitosis is a type of cell division that results in two genetically identical daughter cells. This type of division is crucial for somatic cell growth and tissue repair. In contrast, meiosis is another form of cell division that reduces the chromosome number by half, creating gametes for sexual reproduction.
Key roles of cell division include:

• Growth: Allows organisms to grow by increasing cell number.
• Repair: Replaces damaged or dead cells.
• Reproduction: Generates reproductive cells in sexually reproducing organisms.

Understanding cell division is fundamental in biology as it explains how organisms maintain life, diversity, and continuity across generations.