Q.173 Zoology ⭐ 360° Option Elimination Active

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NEET 2026 Zoology Question 173 Solution

Topic: Human Reproduction · Official NTA Booklet Code 50

Question

The covering of ovum at ovulation is

(1)endometrium
(2)zona radiata
(3)zona pellucida
(4)chorion

✓

Verified Against NTA Final Answer Key

Option (3) : Zona pellucida

📚 Human Reproduction Easy

📋 Given Parameters & Problem Setup

Cell Stage Secondary Oocyte at Ovulation

Nature of Membrane Non-cellular (acellular) glycoprotein coat secreted by oocyte itself

⚡

The 30-Second Exam Hall Shortcut: ⚡ Acellular Glycoprotein Trigger

⏱️ Save ~35 seconds

Non-cellular glycoprotein layer secreted by oocyte = ZONA PELLUCIDA!

1 Look at the defining keywords: "non-cellular glycoprotein coat".

2 Zona pellucida is the acellular translucent glycoprotein layer secreted directly by the secondary oocyte.

3 Corona radiata consists of living follicular/granulosa cells arranged radially.

4 Theca interna is an ovarian follicle stromal layer that produces androgens.

5 Vitelline membrane is the plasma membrane of the egg.

6 Match Option (3) Zona pellucida in under 10 seconds!

🛡️

Why You Can 100% Trust This Shortcut: NCERT Biology · Human Reproduction (Parturition Reflex: Neuroendocrine reflex triggers oxytocin release from maternal pituitary).

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Structure of the Ovulated Secondary Oocyte

During oogenesis, the primary oocyte completes its first meiotic division within the tertiary follicle to form a secondary oocyte and a tiny first polar body. The secondary oocyte forms a new acellular glycoprotein membrane around itself called zona pellucida.

\text{Secondary Oocyte} \xrightarrow{\text{Secretes}} \mathbf{Zona Pellucida (Acellular Glycoprotein Envelope)}

• Zona pellucida contains sperm-binding glycoproteins ZP1, ZP2, and ZP3.

Step 2

Function During Fertilization

Outside the zona pellucida lies the corona radiata, formed of radially elongated follicle/granulosa cells. During fertilization, sperm acrosomal enzymes (hyaluronidase and acrosin) penetrate the corona radiata and digest the zona pellucida. Contact of one sperm induces a cortical reaction in the zona pellucida, blocking polyspermy.

\text{Sperm Contact} \rightarrow \text{Cortical Granule Exocytosis} \rightarrow \text{Hardening of Zona Pellucida (Blocks Polyspermy)}

• Prevents polyspermy and ectopic implantation in the fallopian tube.

⭐

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. Corona radiata is a cellular layer formed of radially arranged granulosa cells, not an acellular glycoprotein coat.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing the cellular outer corona radiata with the acellular inner zona pellucida.

2 B

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Theca interna is a cellular vascular layer of the Graafian follicle that stays behind in the ovary after ovulation to form the corpus luteum.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing follicular wall layers with oocyte coats.

3 C

✓ 100% Correct

Verdict & Scientific Reason:

100% correct. Zona pellucida is the non-cellular glycoprotein coat secreted around the secondary oocyte.

💡

Why this is airtight: None; classic reproductive biology fact.

4 D

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. The vitelline membrane represents the plasma membrane / oolemma of the egg, not the specialized non-cellular coat described.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing plasma membrane with the outer zona pellucida.

⚠️

NTA Trap Alert: Cellular vs. Non-Cellular Egg Layers

Examiners test whether you know which layer is cellular and which is non-cellular. Zona pellucida is NON-CELLULAR (glycoprotein); Corona radiata is CELLULAR (follicle cells).

🛡️ How to avoid the -1 mark: Remember: Zona = Zone (clear, non-cellular ring); Corona = Crown of cells.

📖

Core NEET Syllabus Standard

NEET Biology Core Syllabus · Human Reproduction Standard Benchmark

Core Scientific Principle Tested:

"The secondary oocyte forms a new non-cellular membrane called zona pellucida surrounding it."

Syllabus Focus: Gametogenesis & Ovulation

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

Zona = Zero cells (Non-cellular glycoprotein coat)!

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NEET 2026 Zoology Question 173 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Acellular Glycoprotein Trigger

Step-by-Step Rigorous Workflow & Mathematical Proof

Structure of the Ovulated Secondary Oocyte

Function During Fertilization

360° Option Elimination Engine Key Feature

NTA Trap Alert: Cellular vs. Non-Cellular Egg Layers

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

🔗 Related Questions — Human Reproduction

Structure and Function of Human Spermatozoon

Chronology of Human Gestational Milestones

Comparison of Spermatogenesis vs Oogenesis and Hormonal Control

Terminology of Menstrual Milestones (Menarche vs Menopause)

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