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NEET 2023 Botany Question 134 Solution

Topic: Cell Cycle and Cell Division · Official NTA Booklet Code G5

Question

Among eukaryotes, replication of DNA takes place in -

✓

Verified Against NTA Final Answer Key

Option (3) : S phase

📚 Cell Cycle and Cell Division Easy

📋 Given Parameters & Problem Setup

Event Replication of nuclear DNA

Cell Type Eukaryotes

⚡

The 30-Second Exam Hall Shortcut: ⚡ Cell Cycle S Phase: S = Synthesis of DNA

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The cell cycle interphase consists of G1 (growth), S (synthesis/DNA replication), and G2 (protein synthesis). DNA replication takes place exclusively in the S phase, doubling DNA content from 2C to 4C!

1 G1 phase: Growth, metabolically active, RNA/protein synthesis before DNA replication.

2 S phase: Synthesis phase; DNA replication occurs in nucleus; centriole duplicates in cytoplasm.

3 G2 phase: Tubulin and mitotic protein synthesis.

4 M phase: Nuclear and cytoplasmic division.

5 Match Option (3) S phase.

🛡️

Why You Can 100% Trust This Shortcut: Canonical NCERT Cell Division interphase phase transitions.

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Phases of Interphase

Interphase is subdivided into three distinct sequential phases:

\begin{aligned} \mathbf{G_1\text{ Phase (Gap 1):}} & \quad \text{Metabolic growth, interval between mitosis and DNA synthesis} \\[3pt] \mathbf{S\text{ Phase (Synthesis):}} & \quad \mathbf{\text{DNA replication and doubling of DNA content } (2C \to 4C)} \\[3pt] \mathbf{G_2\text{ Phase (Gap 2):}} & \quad \text{Synthesis of tubulin and proteins for mitosis} \end{aligned}

Step 2

Verbatim NCERT Reference

NCERT states verbatim: "S or synthesis phase marks the period during which DNA synthesis or replication takes place. During this time the amount of DNA per cell doubles. If the initial amount of DNA is denoted as 2C then it increases to 4C."

Step 3

Chromosome Number Invariance

Crucially, while the DNA content doubles from $2C$ to $4C$ , the chromosome number remains unchanged at $2n$ because sister chromatids remain physically united at the centromere until anaphase.

⭐

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4-Option Deep Scan

1 1

✗ Incorrect

Verdict & Scientific Reason:

In G2 phase, proteins (like tubulin) are synthesized in preparation for mitosis while cell growth continues.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing post-replication mitotic preparation with replication itself.

2 2

✗ Incorrect

Verdict & Scientific Reason:

M phase is the stage of chromosome condensation, karyokinesis, and cytokinesis; replication has already concluded.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing chromosome segregation with DNA synthesis.

3 3

✓ 100% Correct

Verdict & Scientific Reason:

DNA replication takes place exclusively during the S (Synthesis) phase of interphase.

💡

Why this is airtight: None; fundamental cell biology.

4 4

✗ Incorrect

Verdict & Scientific Reason:

G1 phase precedes DNA replication; the cell is metabolically active and grows continuously.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing pre-replication preparation with actual replication.

⚠️

NTA Trap Alert: DNA Content vs. Chromosome Number Trap

Students frequently think that because DNA doubles in S phase, the chromosome number doubles too. Chromosome count remains $2n$ ; only DNA content increases from $2C$ to $4C$ .

🛡️ How to avoid the -1 mark: DNA doubles (

2C \to 4C

), but chromosome number stays constant (

2n \to 2n

) in S phase.

📖

Core NEET Syllabus Standard

NCERT Biology · Cell Cycle and Cell Division Standard Benchmark

Core Scientific Principle Tested:

"S or synthesis phase marks the period during which DNA synthesis or replication takes place."

Syllabus Focus: Interphase (S Phase)

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

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NEET 2023 Botany Question 134 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Cell Cycle S Phase: S = Synthesis of DNA

Step-by-Step Rigorous Workflow & Mathematical Proof

Phases of Interphase

Verbatim NCERT Reference

Chromosome Number Invariance

360° Option Elimination Engine Key Feature

NTA Trap Alert: DNA Content vs. Chromosome Number Trap

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

🔗 Related Questions — Cell Cycle and Cell Division

Sequential Phases of the Eukaryotic Cell Cycle

Stages of Meiosis I and Comparison with Mitosis

Function of Spindle Fibers during Mitosis (Chromosome Segregation)

Stages of Mitosis: Spindle Fibre Attachment to Kinetochores

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