Q.171 Zoology ⭐ 360° Option Elimination Active

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NEET 2026 Zoology Question 171 Solution

Topic: Human Health and Disease · Official NTA Booklet Code 50

Question

Colostrum, secreted by mother during initial days of lactation, is abundant in

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Verified Against NTA Final Answer Key

Option (3) : IgA

📚 Human Health and Disease Easy

📋 Given Parameters & Problem Setup

Secretory Fluid Colostrum (yellowish milk of initial days of lactation)

Target Property Predominant antibody providing passive immunity to infant

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The 30-Second Exam Hall Shortcut: ⚡ Secretory Antibody Recall

⏱️ Save ~30 seconds

Colostrum / Tears / Saliva / Mucus = Secretory IgA (Dimer)!

1 Identify keyword: "Colostrum".

2 Recall canonical immunological antibody distribution:

3 IgA: Present in external secretions (colostrum, breast milk, saliva, tears).

4 IgG: Most abundant in serum; only antibody that crosses the placenta.

5 IgE: Mediates allergic reactions and binds mast cells.

6 IgM: Largest antibody (pentamer); first to be produced in primary immune response.

7 Colostrum is famously packed with IgA.

8 Select Option (3) IgA.

🛡️

Why You Can 100% Trust This Shortcut: NCERT Biology · Human Health and Disease (Innate Immunity Barriers: Physical, physiological, cellular, and cytokine barriers).

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Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Composition and Role of Colostrum

The yellowish fluid colostrum secreted by mother during the initial days of lactation has abundant antibodies (IgA) to protect the infant against gastrointestinal and respiratory pathogens.

\text{Colostrum} \xrightarrow{\text{Abundant}} \mathbf{IgA} \xrightarrow{\text{Passive Natural Immunity}} \text{Neonatal Protection}

• This provides natural passive immunity because preformed antibodies are transferred directly to the infant.

Step 2

Structural Adaptation of IgA

Secretory IgA is typically a dimer joined by a J-chain and protected by a secretory component against proteolytic digestion in the infant’s stomach and intestines.

\text{Secretory IgA} = 2 \times (\text{H}_2\text{L}_2) + \text{J-Chain} + \text{Secretory Component}

• IgG provides prenatal passive immunity via placental transfer, whereas IgA provides postnatal passive immunity via colostrum.

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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. IgG is the predominant serum antibody and crosses the placenta into the fetus, but it is not the primary antibody of colostrum.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing placental transfer (IgG) with colostrum (IgA).

2 B

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. IgM is a pentamer and the earliest antibody produced during a primary humoral immune response, not the major antibody in colostrum.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing the first responder antibody (IgM) with maternal milk antibody.

3 C

✓ 100% Correct

Verdict & Scientific Reason:

100% correct. IgA is the predominant immunoglobulin found in colostrum and external mucosal secretions.

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Why this is airtight: None; standard NCERT fact.

4 D

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. IgE is involved in hypersensitivity/allergic reactions and defense against helminth parasites.

⚠️

Student Fallacy (Why candidates pick this trap): Associating IgE with immune protection rather than allergy.

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NTA Trap Alert: IgG vs. IgA Maternal Immunity Trap

Students frequently conflate prenatal maternal protection (IgG through placenta) with postnatal maternal protection (IgA through colostrum).

🛡️ How to avoid the -1 mark: Remember: G = Gestation/Goes through placenta (IgG); A = After birth/Alimentary/colostrum (IgA).

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Core NEET Syllabus Standard

NEET Biology Core Syllabus · Human Health and Disease Standard Benchmark

Core Scientific Principle Tested:

"Colostrum secreted during the initial days of lactation has abundant antibodies (IgA) to protect the infant."

Syllabus Focus: Innate and Acquired Immunity

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

IgA = Ingested by the Infant After birth (Colostrum)!

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NEET 2026 Zoology Question 171 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Secretory Antibody Recall

Step-by-Step Rigorous Workflow & Mathematical Proof

Composition and Role of Colostrum

Structural Adaptation of IgA

360° Option Elimination Engine Key Feature

NTA Trap Alert: IgG vs. IgA Maternal Immunity Trap

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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