Q.18 Botany ⭐ 360° Option Elimination Active

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NEET 2020 Botany Question 18 Solution

Topic: Biotechnology: Principles and Processes · Official NTA Booklet Code E1

Question

In gel electrophoresis, separated DNA fragments can be visualized with the help of:

(1)Acetocarmine in bright blue light
(2)Ethidium bromide in UV radiation
(3)Acetocarmine in UV radiation
(4)Ethidium bromide in infrared radiation

✓

Verified Against NTA Final Answer Key

Option (2) : Ethidium bromide in UV radiation

📚 Biotechnology: Principles and Processes Easy

📋 Given Parameters & Problem Setup

Analytical Technique Agarose Gel Electrophoresis

Target Molecule Separated DNA fragments

Question Objective Identify the staining dye and illumination wavelength for DNA visualization

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The 30-Second Exam Hall Shortcut: ⚡ "EtBr + UV Light = Bright Orange Fluorescent DNA Bands!"

⏱️ Save ~20 seconds

Pure DNA fragments cannot be seen in visible light without staining. Separated DNA is stained with the intercalating fluorophore Ethidium Bromide (EtBr) and visualized under UV radiation, appearing as bright orange bands! Mark Option (2) in 5 seconds.

1 Recall NCERT gel electrophoresis visualization protocol: - You cannot see pure DNA fragments in the visible light without staining. - The separated DNA fragments can be visualized only after staining with a compound known as ethidium bromide followed by exposure to UV radiation. - You can see bright orange coloured bands of DNA in a UV exposed gel.

2 Identify dye: Ethidium bromide (EtBr).

3 Identify light source: Ultraviolet (UV) radiation.

4 Select Option (2): Ethidium bromide in UV radiation.

🛡️

Why You Can 100% Trust This Shortcut: NCERT Biology · Biotechnology: Principles and Processes (Separation and Isolation of DNA Fragments: The separated DNA fragments can be visualised only after staining the DNA with a compound known as ethidium bromide followed by exposure to UV radiation. You can see bright orange coloured bands of DNA).

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Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Biophysical Principle of DNA Visualization in Agarose Gels

Because nucleic acids have no chromophores absorbing in the visible spectrum, resolved double-stranded DNA bands are completely invisible to the naked eye: - Intercalating Fluorescent Dye: The gel is stained with ethidium bromide (EtBr), a planar polycyclic fluorescent molecule that intercalates between stacked adjacent nitrogenous base pairs of the DNA duplex. - Ultraviolet Transillumination: When irradiated with ultraviolet (UV) radiation (~300–360 nm), the hydrophobic microenvironment between base pairs enhances the fluorescence quantum yield of EtBr dramatically. - Optical Signal: The excited dye-DNA complex emits intense visible fluorescence in the orange spectrum, revealing bright orange coloured bands marking the precise migratory positions of DNA fragments.

\text{Duplex DNA} \xrightarrow[\text{Intercalation}]{\mathbf{Ethidium\,Bromide\,(EtBr)}} [\text{DNA-EtBr Complex}] \xrightarrow{\mathbf{UV\,Radiation}} \mathbf{Bright\,Orange\,Fluorescent\,Bands}

Step 2

Elimination of Distractor Stains and Radiation Sources

- Acetocarmine: A biological nuclear/chromosomal stain used in squash preparations for light microscopy during cytogenetics/mitosis, not agarose gel electrophoresis. - Infrared / Visible light: Infrared radiation and blue light do not provide the necessary photonic excitation energy for ethidium bromide fluorescence.

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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. Acetocarmine is used to stain squashed root-tip chromosomes under light microscopy.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing mitotic cytogenetic stains with agarose gel electrophoresis.

2 B

✓ 100% Correct

Verdict & Scientific Reason:

Correct. EtBr staining followed by UV transillumination is the canonical method to visualize DNA bands.

💡

Why this is airtight: None. Direct recall of textbook biotechnology protocols.

3 C

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Acetocarmine is not a fluorescent DNA dye used with UV radiation.

⚠️

Student Fallacy (Why candidates pick this trap): Combining a cytogenetic dye with UV illumination.

4 D

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Infrared radiation does not excite ethidium bromide.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing high-energy UV light with low-energy infrared.

⚠️

NTA Trap Alert: Dye and Radiation Cross-Permutation Trap

NTA creates 4 options by cross-pairing two dyes (Ethidium bromide vs Acetocarmine) with different light sources (UV vs Blue light vs Infrared). Memorize the exact combination: EtBr + UV radiation.

🛡️ How to avoid the -1 mark: Remember: EtBr + UV = Bright Orange bands.

📖

Core NEET Syllabus Standard

NEET / NCERT Biology · Biotechnology: Principles and Processes Standard Benchmark

Core Scientific Principle Tested:

"DNA fragments in gel electrophoresis are visualized using ethidium bromide under UV radiation."

Syllabus Focus: Agarose Gel Electrophoresis

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

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NEET 2020 Botany Question 18 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ "EtBr + UV Light = Bright Orange Fluorescent DNA Bands!"

Step-by-Step Rigorous Workflow & Mathematical Proof

Biophysical Principle of DNA Visualization in Agarose Gels

Elimination of Distractor Stains and Radiation Sources

360° Option Elimination Engine Key Feature

NTA Trap Alert: Dye and Radiation Cross-Permutation Trap

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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