M Phase (Mitosis) is the most dynamic stage of the cell cycle, where a single cell divides into two identical daughter cells. This process ensures that the chromosome number remains constant, which is why mitosis is called equational division.
In this post, we will cover all stages of mitosis including Prophase, Metaphase, Anaphase, and Telophase, along with Cytokinesis.
Detailed diagrams and NEET-oriented MCQs are included to strengthen your understanding.
Introduction to M Phase
The M Phase (Mitotic phase) is the most dramatic period of the cell cycle, involving a major reorganization of virtually all components of the cell. Since the number of chromosomes in the parent and daughter cells is the same, it is also called equational division.
Mitosis is divided into four main nuclear stages (Karyokinesis):
Prophase
Metaphase
Anaphase
Telophase
1. Prophase (The First Stage)
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| The chromosomal material condenses to form compact mitotic chromosomes. You can see the chromatin fibers beginning to coil and shorten. Late Prophase:  |
Chromosome Condensation: Chromosomal material condenses to form compact mitotic chromosomes.
Structure: Each chromosome is seen to be composed of two chromatids attached together at the centromere.
Organelles Disappear: The nucleolus, endoplasmic reticulum (ER), and Golgi complex disappear by the end of prophase.
2. Metaphase:
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Metaphase (The Alignment):  |
Spindle Fibers: Spindle fibers attach to the kinetochores of chromosomes.
Metaphase Plate: Chromosomes are pulled to the spindle equator and align along the metaphase plate.
Key Fact: This is the best stage to study the morphology and shape of chromosomes.
3. Anaphase (The Splitting Stage):
At the onset of this stage, each centromere splits simultaneously, and the sister chromatids (now daughter chromosomes) begin their migration toward opposite poles of the cell.
At the onset of this stage, each centromere splits simultaneously, and the sister chromatids (now daughter chromosomes) begin their migration toward opposite poles of the cell.
Centromere Split: Each centromere splits simultaneously, and chromatids separate.
Migration: Chromatids (now referred to as daughter chromosomes) move toward opposite poles.
4. Telophase (The Final Stage):
Telophase: The final stage of karyokinesis. Chromosomes reach their respective poles and lose their individuality by decondensing. The nuclear envelope, nucleolus, Golgi complex, and ER reappear during this stage.
Decondensation: Chromosomes reach their respective poles and lose their individuality.
Reformations: Nuclear envelope, nucleolus, Golgi complex, and ER reappear.
Study Note: Telophase is often called the "Reverse of Prophase" because everything that disappeared in Prophase (like the nuclear envelope and nucleolus) comes back here.
Cytokinesis (Division of Cytoplasm)
Mitosis is not just about dividing the nucleus (Karyokinesis); it also requires the division of the cytoplasm, known as Cytokinesis.
In Animal Cells: Occurs by the appearance of a furrow in the plasma membrane.
In Plant Cells: Occurs by the formation of a cell plate that starts from the center and grows outward.
Cytokinesis: The Final Split
While Karyokinesis deals with the division of the nucleus, Cytokinesis is the actual division of the cytoplasm into two daughter cells. This process ensures that each new cell receives a nucleus and the necessary organelles.
1. Cytokinesis in Animal Cells
Cleavage Furrow: It starts with the appearance of a furrow in the plasma membrane.
Centripetal Movement: The furrow gradually deepens and moves inward (centripetally) until it meets in the center, dividing the cell into two.
2. Cytokinesis in Plant Cells
Cell Plate Formation: Unlike animal cells, plant cells have a rigid cell wall. Therefore, they divide by forming a cell plate.
Centrifugal Movement: The division starts in the center of the cell and grows outward (centrifugally) toward the existing lateral walls.
Middle Lamella: The cell plate represents the middle lamella between the walls of two adjacent cells.
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High-Yield NEET Note: SyncytiumIn some organisms, karyokinesis is not followed by cytokinesis. This results in a multi-nucleate condition known as a Syncytium (e.g., liquid endosperm in coconut). Summary Table: Comparison of Mitosis Phases
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📌 High-Yield Points for NEET:
Mitosis is Equational Division: Chromosome number remains constant (2n -> 2n).
Significance: It helps in cell repair, growth of multicellular organisms, and replacement of dead cells.
Test Your Knowledge: Mitosis & Cytokinesis Quiz
Q1. Which of the following stages of mitosis is considered the best for studying the morphology and shape of chromosomes? A. Prophase
B. Metaphase
C. Anaphase
D. Telophase
Answer: B (Metaphase). During this stage, chromosomes are most condensed and aligned at the equator, making them clearly visible.
Q2. The splitting of centromeres and the separation of sister chromatids occur during which phase? A. S-phase
B. Metaphase
C. Anaphase
D. G2 phase
Answer: C (Anaphase). This is the critical step where daughter chromosomes begin their migration toward opposite poles.
Q3. How does cytokinesis in a plant cell differ from that in an animal cell? A. Plant cells divide by furrowing of the plasma membrane.
B. Plant cells divide by the formation of a cell plate from the center outward.
C. Animal cells form a cell plate during division.
D. There is no difference in the mechanism of cytokinesis.
Answer: B (Plant cells divide by the formation of a cell plate from the center outward). Animal cells divide centripetally via a cleavage furrow, whereas plant cells divide centrifugally via a cell plate.
Q4. Mitosis is called 'equational division' because: A. It occurs only in somatic cells.
B. It results in the doubling of the chromosome number.
C. The daughter cells have the same number of chromosomes as the parent cell.
D. It involves two rounds of nuclear division.
Answer: C (The daughter cells have the same number of chromosomes as the parent cell). This ensures genetic stability across generations of cells.
Q5. If karyokinesis is not followed by cytokinesis, it leads to the formation of: A. Diploid cells
B. Haploid cells
C. Syncytium (multinucleate condition)
D. Cell plate
Answer: C (Syncytium). Failure of cytoplasmic division results in a single cell containing multiple nuclei, such as in liquid coconut endosperm.
Mitosis is a crucial process responsible for growth, repair, and maintenance of the body. It involves precise distribution of chromosomes through Prophase, Metaphase, Anaphase, and Telophase, followed by Cytokinesis.
Understanding the sequence of events, chromosome behavior, and differences between plant and animal cytokinesis is extremely important for NEET exams.
👉 Next Topic: Meiosis – Reduction Division (Part 3)
⬅️Previous: Cell Cycle Phases (Part 1)🏠 Index: Complete Cell Notes ➡️ Next: Meiosis (Part 3)
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