Q.72 Zoology ⭐ 360° Option Elimination Active

NEET 2020 Zoology Question 72 Solution

Topic: Cell Cycle and Cell Division · Official NTA Booklet Code E1

Question

Some dividing cells exit the cell cycle and enter vegetative inactive stage. This is called quiescent stage (G0). This process occurs at the end of:

(1)M phase
(2)G1 phase
(3)S phase
(4)G2 phase

✓

Verified Against NTA Final Answer Key

Option (2) : G1 phase

📚 Cell Cycle and Cell Division Medium

📋 Given Parameters & Problem Setup

Cellular Stage Quiescent stage (G0 stage)

Physiological State Metabolically active but no longer proliferating unless called upon

Question Objective Identify which cell cycle phase cells exit at the end of to enter G0

⚡

The 30-Second Exam Hall Shortcut: ⚡ "Cells Exit G1 Phase to Enter Quiescent G0 Stage!"

⏱️ 25 seconds

Some cells in adult animals (like heart cells and neurons) do not divide further. These cells exit the cycle by suspending proliferation at the restriction/decision point at the END of G1 phase to enter the quiescent stage (G0). Mark G1 phase (Option 2) in 5 seconds!

1 Recall NCERT text: "Some cells in the adult animal do not appear to exhibit division... These cells that do not divide further exit G1 phase to enter an inactive stage called quiescent stage (G0) of the cell cycle."

2 G0 cells remain metabolically active but do not replicate DNA (they never enter S phase).

3 Thus, exit occurs at the end of G1 phase.

4 Select Option (2) G1 phase.

🛡️

Why You Can 100% Trust This Shortcut: NCERT Biology · Cell Cycle and Cell Division (Phases of Cell Cycle: G0 Quiescent Stage)

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Understand the G0 Phase Concept

Cells that do not continue dividing exit the regular progression of the cell cycle and enter a specialized non-proliferative resting state designated as the quiescent stage (G0).

Step 2

Specific Exit Point from the Cycle

NCERT states verbatim: "These cells that do not divide further exit G1 phase to enter an inactive stage called quiescent stage (G0) of the cell cycle."

Step 3

Metabolic Characteristics of G0 Cells

Cells in G0 stage remain metabolically active, maintaining basic cellular functions and tissue homeostasis, but no longer proliferate unless specifically stimulated (e.g., hepatocytes following partial hepatectomy).

Step 4

Differentiate Alternative Phases

M phase is followed by cytokinesis, delivering daughter cells into G1; S phase is committed DNA replication; G2 phase prepares for mitosis. The commitment decision to divide or withdraw occurs in G1.

⭐

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 A

✗ Incorrect

Verdict & Scientific Reason:

Incorrect; after M phase, cells normally enter G1 phase before deciding whether to proceed to S phase or exit into G0.

⚠️

Student Fallacy (Why candidates pick this trap): Thinking that exiting division immediately after mitosis means exiting M phase.

2 B

✓ 100% Correct

Verdict & Scientific Reason:

Factually exact; cells exit at the restriction point of the G1 phase to enter the G0 quiescent state.

💡

Why this is airtight: None; explicit textbook statement.

3 C

✗ Incorrect

Verdict & Scientific Reason:

Incorrect; once a cell enters S phase, DNA replication has begun and the cell is committed to dividing, unable to enter G0.

⚠️

Student Fallacy (Why candidates pick this trap): Misunderstanding the cell cycle commitment point.

4 D

✗ Incorrect

Verdict & Scientific Reason:

Incorrect; G2 cells possess duplicated DNA (4C) and are preparing for mitosis, not resting in G0.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing post-synthetic pause with quiescent G0.

⚠️

NTA Trap Alert: Exit G1 vs Exit M Phase Phrasing

NCERT explicitly states: "cells exit G1 phase to enter G0". The checkpoint determining whether to replicate DNA (S phase) or become quiescent (G0) is in G1.

🛡️ How to avoid the -1 mark: Commit to memory: G0 entry = EXIT FROM G1 PHASE!

📖

Core NEET Syllabus Standard

Zoology · Cell Cycle and Cell Division Standard Benchmark

Core Scientific Principle Tested:

Syllabus Focus: Quiescent Stage (G0) Entry: Cells Exit Cell Cycle at the End of G1 Phase

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

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NEET 2020 Zoology Question 72 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ "Cells Exit G1 Phase to Enter Quiescent G0 Stage!"

Step-by-Step Rigorous Workflow & Mathematical Proof

Understand the G0 Phase Concept

Specific Exit Point from the Cycle

Metabolic Characteristics of G0 Cells

Differentiate Alternative Phases

360° Option Elimination Engine Key Feature

NTA Trap Alert: Exit G1 vs Exit M Phase Phrasing

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

🔗 Related Questions — Cell Cycle and Cell Division

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Stages of Mitosis: Spindle Fibre Attachment to Kinetochores

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