Q.164 Zoology ⭐ 360° Option Elimination Active

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NEET 2021 Zoology Question 164 Solution

Topic: Cell Cycle and Cell Division · Official NTA Booklet Code M1

Question

The centriole undergoes duplication during:

(1)S-phase
(2)Prophase
(3)Metaphase
(4)G2 phase

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Verified Against NTA Final Answer Key

Option (1) : S-phase

📚 Cell Cycle and Cell Division Easy

📋 Given Parameters & Problem Setup

Organelle Centriole

Event Duplication during cell cycle

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The 30-Second Exam Hall Shortcut: ⚡ "S-Phase: DNA Duplicates in Nucleus, Centrioles Duplicate in Cytoplasm"

⏱️ Save ~25 seconds

NCERT verbatim rule: "In animal cells, during the S-phase, DNA replication begins in the nucleus, and the centriole duplicates in the cytoplasm." Both core duplication events happen synchronously in S-phase! Match Option (1) in 3 seconds!

1 Recall the hallmark events of S-phase in animal cells.

2 Nuclear event = DNA replication (2C → 4C).

3 Cytoplasmic event = Centriole duplication (one pair becomes two pairs).

4 Match Option (1).

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Why You Can 100% Trust This Shortcut: NCERT Biology · Cell Cycle and Cell Division (Interphase S-phase: DNA replicates in the nucleus while centriole duplicates in the cytoplasm of animal cells).

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Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Synchronized Nuclear and Cytoplasmic Events of S-Phase

The synthesis ( $S$ ) phase of interphase is characterized by coordinated replication of genetic and spindle-organizing structures in animal cells: - In the Nucleus: Semi-conservative DNA replication occurs, doubling the DNA content from $2C$ to $4C$ . - In the Cytoplasm: The centrosome, containing a pair of orthogonally oriented centrioles, duplicates so that two centrosomes (each with two centrioles) are formed. - This duplication is indispensable because each centrosome will later migrate to opposite poles during prophase to organize the mitotic spindle apparatus.

\text{S-Phase Events} \implies \begin{cases} \textbf{Nucleus:} & \text{DNA Replication } (2C \rightarrow 4C) \\[3pt] \textbf{Cytoplasm:} & \mathbf{Centriole\ Duplication} \end{cases}

Step 2

Evaluation of Other Cell Cycle Stages

- $G_1$ phase: Gap 1 involves metabolic growth, RNA and protein synthesis; centrioles do not replicate. - $G_2$ phase: Gap 2 involves synthesis of tubulin and preparations for mitosis. - Prophase: Centrosomes (already duplicated during S-phase) begin their bipolar migration; aster rays and spindle fibers assemble. - Metaphase: Chromosomes align on the equatorial plate.

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360° Option Elimination Engine Key Feature

Diagnose every choice: Know exactly why the right option works and why distractors fail.

4-Option Deep Scan

1 1

✓ 100% Correct

Verdict & Scientific Reason:

Correct. Centriole duplication occurs concurrently with DNA replication during the S phase of interphase in the cytoplasm of animal cells.

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Why this is airtight: None. Textbook definition.

2 2

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. During prophase, duplicated centrosomes migrate to opposite poles; they do not duplicate during prophase.

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Student Fallacy (Why candidates pick this trap): Students see centrosomes moving apart in prophase diagrams and wrongly conclude they are duplicating there.

3 3

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. In metaphase, centrioles reside at established spindle poles and align chromosomes at the equator.

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Student Fallacy (Why candidates pick this trap): Confusing metaphase spindle organization with organelle duplication.

4 4

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Centriole duplication is already finished by the time the cell exits S-phase and enters G2.

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Student Fallacy (Why candidates pick this trap): Assuming pre-mitotic organelle duplication continues through G2.

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NTA Trap Alert: Centriole Migration (Prophase) vs Duplication (S-Phase)

Candidates routinely confuse the duplication of centrioles (which takes place invisibly in the cytoplasm during S-phase) with the visible separation/migration of centrioles to opposite poles (which occurs during prophase).

🛡️ How to avoid the -1 mark: Remember: Duplication = S-phase; Separation/Migration to poles = Prophase.

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Core NEET Syllabus Standard

NEET / NCERT Biology · Cell Cycle and Cell Division Standard Benchmark

Core Scientific Principle Tested:

"In animal cells, DNA replication occurs in the nucleus and centriole duplication occurs in the cytoplasm during S-phase."

Syllabus Focus: S-Phase of Cell Cycle

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

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NEET 2021 Zoology Question 164 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ "S-Phase: DNA Duplicates in Nucleus, Centrioles Duplicate in Cytoplasm"

Step-by-Step Rigorous Workflow & Mathematical Proof

Synchronized Nuclear and Cytoplasmic Events of S-Phase

Evaluation of Other Cell Cycle Stages

360° Option Elimination Engine Key Feature

NTA Trap Alert: Centriole Migration (Prophase) vs Duplication (S-Phase)

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

🔗 Related Questions — Cell Cycle and Cell Division

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Function of Spindle Fibers during Mitosis (Chromosome Segregation)

Stages of Mitosis: Spindle Fibre Attachment to Kinetochores

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