Cell Cycle and Cell Division is one of the most important topics in NEET Biology. In this part, we will understand the different phases of the cell cycle including G1, S, G2, and M phase in a simple and clear way.
This post includes concept-based explanations, diagram-focused learning, and NEET-oriented MCQs to help you revise the topic effectively and improve your exam performance.
Introduction to Cell Cycle
Growth and reproduction are fundamental characteristics of all living organisms. A cell reproduces by dividing into two, with each parental cell giving rise to two daughter cells. This cycle of synthesis, growth, and division is known as the Cell Cycle.
Did You Know? A typical human cell divides once every 24 hours, whereas a yeast cell can complete the cycle in just 90 minutes.
Phases of the Cell Cycle
The cell cycle is divided into two basic phases:
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| "Diagrammatic representation of the Cell Cycle showing Interphase (G1, S, G2) and M Phase, including the G0 (Quiescent) stage." |
Interphase: The phase between two successive M phases. It lasts for more than 95% of the total duration of the cycle.
M Phase (Mitosis Phase): The actual phase where nuclear and cytoplasmic division occurs.
1. Interphase (The Preparation Phase)
Interphase, though often called the "resting phase," is a time of intense metabolic activity. It is further divided into three stages:
G1 Phase (Gap 1):
"A colorful circular diagram illustrating the various phases of the Cell Cycle, including the Interphase (I) stages (G1, S, G2), the Mitotic phase (M), and the G0 quiescent stage." The interval between mitosis and the start of DNA replication.
The cell is metabolically active and grows continuously but does not yet replicate its DNA.
S Phase (Synthesis Phase):
"Diagram of the Cell Cycle highlighting the S phase (DNA Synthesis), where genetic material duplicates before division." DNA replication occurs during this stage.
"A comprehensive diagram of the DNA replication process, illustrating key enzymes like Helicase, Topoisomerase, and DNA Polymerase, along with leading and lagging strand synthesis." The amount of DNA per cell doubles (from 2C to 4C), but the chromosome number remains the same (if the cell was 2n, it stays 2n).
In animal cells, the centriole duplicates in the cytoplasm.
G2 Phase (Gap 2):
"Diagrammatic representation of the Gap 2 (G2) phase of Interphase, showing cell growth, protein synthesis, and the critical 'double-checking' of duplicate chromosomes for errors and repairs before Mitosis." Proteins are synthesized in preparation for mitosis while cell growth continues.
2. The G0 Phase (Quiescent Stage)
"Diagram of the cell cycle showing the transition from the G1 phase to the G0 (gap 0) phase, where cells exit the active division cycle to enter a quiescent, inactive state."
Some cells in the adult body do not divide (e.g., Heart cells) or divide only to replace injured cells. These cells exit the G1 phase and enter an inactive stage called G0.
Cells in this stage remain metabolically active.
They do not proliferate unless called upon by the body's requirements.
📌 High-Yield Facts for NEET
Duration: Interphase > 95% of cycle time.
S-Phase Rule: DNA content doubles (2C \rightarrow 4C), but Chromosome number (2n) remains unchanged.
Checkpoints: The transition between phases is strictly regulated by proteins (Cyclins and CDKs).
Cell Cycle & Interphase: Multiple Choice Questions (Part 1)
1. Mature nerve cells usually do not divide. These cells are considered to be in which phase of the cell cycle?
(A) G1 phase
(B) S phase
(C) G0 phase (Correct Answer)
(D) G2 phase
Explanation: Cells that do not divide further exit the G1 phase to enter an inactive stage called the G0 phase or the Quiescent stage.
2. In a typical 24-hour human cell cycle, what percentage of time is occupied by the Interphase?
(A) Less than 5%
(B) 50%
(C) More than 95% (Correct Answer)
(D) 25%
Explanation: The Interphase is the longest phase, lasting for more than 95% of the total duration of the cell cycle.
3. During the S phase (Synthesis phase) of the cell cycle, which of the following occurs?
(A) DNA amount doubles, but the chromosome number remains the same (Correct Answer)
(B) Both DNA and chromosome numbers double
(C) DNA amount remains the same, but chromosome number doubles
(D) Neither DNA nor chromosome number changes
Explanation: In the S phase, DNA replication doubles the amount of DNA (2C to 4C), but the chromosome number (2n) stays unchanged.
4. In animal cells, centriole duplication occurs during which phase and where?
(A) G1 phase, in the nucleus
(B) S phase, in the cytoplasm (Correct Answer)
(C) G2 phase, in the cytoplasm
(D) M phase, in the nucleus
Explanation: During the S phase, while DNA replicates in the nucleus, the centriole duplicates in the cytoplasm.
5. In which phase are proteins (like tubulin) synthesized for the preparation of mitosis?
(A) G1 phase
(B) S phase
(C) G2 phase (Correct Answer)
(D) M phase
Explanation: The G2 phase is the final preparation stage where specific proteins like tubulin are synthesized for spindle formation during mitosis.
6. What is the correct sequence of phases in the cell cycle?
(A) S \rightarrow G1 \rightarrow G2 \rightarrow M
(B) G1 \rightarrow S \rightarrow G2 \rightarrow M (Correct Answer)
(C) M \rightarrow G1 \rightarrow G2 \rightarrow S
(D) G2 \rightarrow M \rightarrow G1 \rightarrow S
Explanation: The cycle always proceeds from the first growth phase (G1), followed by synthesis (S), second growth (G2), and finally division (M).
7. How long does it take for a Yeast cell to complete one cell cycle?
(A) 24 hours
(B) 60 minutes
(C) 90 minutes (Correct Answer)
(D) 10 hours
Explanation: Unlike human cells, Yeast cells are very fast and can complete a full cycle in just 90 minutes.
8. Which of the following is true regarding the G0 phase?
(A) Cells become metabolically inactive
(B) Cells continue to divide rapidly
(C) Cells are metabolically active but no longer proliferate (Correct Answer)
(D) Cells undergo programmed cell death
Explanation: Cells in the G0 stage remain functionally and metabolically active but stop dividing unless specifically required.
9. Why was the Interphase historically called the "Resting Phase"?
(A) Because the cell goes to sleep
(B) Because there is no visible division seen under a microscope (Correct Answer)
(C) Because metabolic activity stops
(D) Because the cell stops taking in nutrients
Explanation: Since no dramatic structural changes like chromosome separation are visible under a microscope during this time, it was once mislabeled as a resting phase.
10. In which phase is the enzyme DNA Polymerase most active?
(A) G1 phase
(B) S phase (Correct Answer)
(C) G2 phase
(D) M phase
Explanation: DNA Polymerase is the primary enzyme for DNA replication, which occurs exclusively during the S phase.
 – Class 11 NEET Notes + MCQ){kind=link}
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