Q.92 Botany ⭐ 360° Option Elimination Active

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NEET 2025 Botany Question 92 Solution

Topic: Biotechnology: Principles and Processes · Official NTA Booklet Code 45

Question

Polymerase chain reaction (PCR) amplifies DNA following the equation.

✓

Verified Against NTA Final Answer Key

Option (2) : 2ⁿ

📚 Biotechnology: Principles and Processes Easy

📋 Given Parameters & Problem Setup

Technique Polymerase Chain Reaction (PCR)

Process Characteristic Repeated thermal cycles of Denaturation, Annealing, and Extension

Variable n Number of PCR cycles

⚡

The 30-Second Exam Hall Shortcut: ⚡ Binary Doubling Law in PCR

⏱️ Save ~20 seconds

Each PCR cycle doubles the target DNA! Cycle 1: 2¹ = 2; Cycle 2: 2² = 4; Cycle 3: 2³ = 8; After n cycles: 2ⁿ copies per template! ⟹ Equation is 2ⁿ!

1 Recognize geometric progression: In PCR, each cycle involves synthesis of a complementary strand for every available template strand.

2 1 initial DNA duplex yields 2 copies after 1st cycle (2¹).

3 2 copies yield 4 copies after 2nd cycle (2²).

4 4 copies yield 8 copies after 3rd cycle (2³).

5 In general, after n cycles of amplification, the total theoretical yield from 1 template molecule is 2ⁿ.

6 Match Option (2) in under 5 seconds!

🛡️

Why You Can 100% Trust This Shortcut: Polymerase Chain Reaction Thermocycling (NCERT Biology · Biotechnology: Principles and Processes: Denaturation -> Annealing -> Extension).

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Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Mechanism of PCR Amplification

PCR involves three successive steps repeated over multiple thermal cycles: denaturation of double-stranded DNA (~94 °C), primer annealing (~54 °C), and primer extension by thermostable Taq DNA polymerase (~72 °C):

\text{Template DNA} \xrightarrow{\text{Cycle 1}} 2 \xrightarrow{\text{Cycle 2}} 4 \xrightarrow{\text{Cycle 3}} 8 \dots \xrightarrow{\text{Cycle } n} 2^n

• Because both strands of every double helix serve as templates in subsequent cycles, the population of target DNA molecules doubles in every completed cycle.

Step 2

Mathematical Formulation of PCR Yield

For an initial population of N₀ template DNA molecules amplified over n cycles:

N_n = N_0 \times 2^n

• For a single initial starting molecule (N₀ = 1), the number of amplified copies is given by the power equation 2ⁿ.
• After 30 cycles, approximately 2³⁰ (over 1 billion) copies are generated.
• Matches Option (2) 2ⁿ.

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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 A

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Polynomial square relation rather than exponential doubling.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing base and exponent.

2 B

✓ 100% Correct

Verdict & Scientific Reason:

100% correct. DNA doubles every cycle, following the exponential relation 2ⁿ.

💡

Why this is airtight: None; basic PCR principle.

3 C

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Linear progression equation.

⚠️

Student Fallacy (Why candidates pick this trap): Assuming linear addition instead of geometric multiplication.

4 D

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Arbitrary non-exponential distractor.

⚠️

Student Fallacy (Why candidates pick this trap): Flawed mathematical model.

⚠️

NTA Trap Alert: Confusing Linear Addition (2n) with Exponential Doubling (2ⁿ)

PCR is a chain reaction, meaning newly formed products become templates for the next round. This produces exponential doubling (2ⁿ), NOT linear growth (2n)!

🛡️ How to avoid the -1 mark: Remember: 1 ⟶ 2 ⟶ 4 ⟶ 8 ⟶ 16 ⟹ Powers of 2: 2ⁿ!

📖

Core NEET Syllabus Standard

NEET Biology Core Syllabus · Biotechnology: Principles and Processes Standard Benchmark

Core Scientific Principle Tested:

"PCR amplifies DNA exponentially according to the equation 2ⁿ."

Syllabus Focus: Amplification of Gene of Interest using PCR

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

Doubling each cycle: 2 × 2 × 2... n times = 2ⁿ (Option 2)!

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NEET 2025 Botany Question 92 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Binary Doubling Law in PCR

Step-by-Step Rigorous Workflow & Mathematical Proof

Mechanism of PCR Amplification

Mathematical Formulation of PCR Yield

360° Option Elimination Engine Key Feature

NTA Trap Alert: Confusing Linear Addition (2n) with Exponential Doubling (2ⁿ)

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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