Q.168 Zoology ⭐ 360° Option Elimination Active

NEET 2023 Zoology Question 168 Solution

Topic: Human Reproduction · Official NTA Booklet Code G5

Question

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R. Assertion A: Endometrium is necessary for implantation of blastocyst. Reason R: In the absence of fertilization, the corpus luteum degenerates that causes disintegration of endometrium. In the light of the above statements, choose the correct answer from the options given below:

(1)A is false but R is true.
(2)Both A and R are true and R is the correct explanation of A.
(3)Both A and R are true but R is NOT the correct explanation of A.
(4)A is true but R is false.

✓

Verified Against NTA Final Answer Key

Option (3) : Both A and R are true but R is NOT the correct explanation of A.

📚 Human Reproduction Medium

📋 Given Parameters & Problem Setup

Assertion (A) Endometrium is necessary for implantation of blastocyst.

Reason (R) In absence of fertilization, corpus luteum degenerates that causes disintegration of endometrium.

⚡

The 30-Second Exam Hall Shortcut: ⚡ Implantation Requirement vs. Menstruation Disintegration Trap

⏱️ Save ~25 seconds

Assertion is TRUE (endometrium provides the vascular bed for blastocyst implantation). Reason is TRUE (corpus luteum degeneration in unfertilized cycles causes endometrial sloughing). But Reason describes the failure/absence of pregnancy; it does NOT explain why endometrium is necessary for implantation! Select Option (3)!

1 Assertion: Endometrium is essential for blastocyst implantation and pregnancy -> True.

2 Reason: Lack of fertilization causes luteolysis, dropping progesterone and sloughing the endometrium -> True.

3 Test explanation: Does the sloughing of endometrium in non-pregnant cycles explain WHY the endometrium is required for implantation in pregnant cycles? No, it explains menstruation!

4 Select Option (3) Both A and R are true but R is NOT the correct explanation of A.

🛡️

Why You Can 100% Trust This Shortcut: Canonical NCERT Human Reproduction ovarian-uterine synchronization logic.

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Evaluation of Assertion A (Implantation Biology)

Following fertilization and cleavage in the fallopian tube, the blastocyst reaches the uterine cavity. The trophoblast layer attaches to the glandular, highly vascularized uterine endometrium, embedding the embryo in the process known as implantation:

\text{Blastocyst (Trophoblast)} \xrightarrow{\text{Implantation}} \text{Endometrium} \implies \text{Assertion A is } \mathbf{\text{TRUE}}

Step 2

Evaluation of Reason R (Luteolysis and Menstruation)

In an unfertilized ovarian cycle, declining LH levels lead to the regression of the corpus luteum into a fibrotic scar (corpus albicans). The subsequent collapse of circulating progesterone withdraws hormonal support, causing spiral arteriolar spasm, necrosis, and menstrual disintegration of the stratum functionale:

\text{No Fertilisation} \implies \text{Luteolysis } \implies \text{Progesterone } \downarrow \implies \text{Endometrium Disintegration} \implies \text{Reason R is } \mathbf{\text{TRUE}}

Step 3

Causal Linkage Evaluation

Assertion states that the endometrium is necessary for implantation. The biological explanation for this is that the endometrium provides the rich vascular supply, decidual reaction, and placental anchorage required to sustain fetal development. Reason explains why menstruation occurs in the *absence* of pregnancy. Thus, R does NOT explain A.

⭐

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 1

✗ Incorrect

Verdict & Scientific Reason:

Assertion is factually true: implantation cannot occur without a receptive endometrium.

⚠️

Student Fallacy (Why candidates pick this trap): Doubting whether endometrium is necessary for implantation.

2 2

✗ Incorrect

Verdict & Scientific Reason:

Reason does not provide the causal physiological basis for Assertion.

⚠️

Student Fallacy (Why candidates pick this trap): Assuming any two true statements related to the endometrium must explain each other.

3 3

✓ 100% Correct

Verdict & Scientific Reason:

Both statements are accurate NCERT physiological facts, but Reason describes menstrual shedding rather than the implantation mechanism.

💡

Why this is airtight: None; rigorous causal discrimination.

4 4

✗ Incorrect

Verdict & Scientific Reason:

Reason is factually true: luteolysis directly triggers endometrial disintegration.

⚠️

Student Fallacy (Why candidates pick this trap): Doubting the role of corpus luteum in maintaining the endometrium.

⚠️

NTA Trap Alert: Topic Association vs. True Causality Trap

Both Assertion and Reason mention "endometrium", so students assume Reason automatically explains Assertion. One describes pregnancy (implantation), while the other describes failure of pregnancy (menstruation).

🛡️ How to avoid the -1 mark: Ask: "Does Reason explain WHY Assertion happens?" Here, luteolysis does not explain why an embryo needs the endometrium.

📖

Core NEET Syllabus Standard

NCERT Biology · Human Reproduction Standard Benchmark

Core Scientific Principle Tested:

"The endometrium is necessary for implantation of the blastocyst and other events of pregnancy. In absence of fertilisation, corpus luteum degenerates causing disintegration of endometrium."

Syllabus Focus: Implantation & Menstrual Cycle

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

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NEET 2023 Zoology Question 168 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Implantation Requirement vs. Menstruation Disintegration Trap

Step-by-Step Rigorous Workflow & Mathematical Proof

Evaluation of Assertion A (Implantation Biology)

Evaluation of Reason R (Luteolysis and Menstruation)

Causal Linkage Evaluation

360° Option Elimination Engine Key Feature

NTA Trap Alert: Topic Association vs. True Causality Trap

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

🔗 Related Questions — Human Reproduction

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