Q.102 Botany ⭐ 360° Option Elimination Active

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NEET 2021 Botany Question 102 Solution

Topic: Sexual Reproduction in Flowering Plants · Official NTA Booklet Code M1

Question

A typical angiosperm embryo sac at maturity is:

(1)8-nucleate and 7-celled
(2)7-nucleate and 8-celled
(3)7-nucleate and 7-celled
(4)8-nucleate and 8-celled

✓

Verified Against NTA Final Answer Key

Option (1) : 8-nucleate and 7-celled

📚 Sexual Reproduction in Flowering Plants Easy

📋 Given Parameters & Problem Setup

Structure Typical angiosperm embryo sac (Polygonum type female gametophyte)

Developmental Stage At maturity

⚡

The 30-Second Exam Hall Shortcut: ⚡ "7-Celled, 8-Nucleate" Polygonum Formula

⏱️ Save ~20 seconds

The classic monosporic angiosperm embryo sac contains 3 antipodals + 3 egg apparatus cells (2 synergids + 1 egg) + 1 large central cell with 2 polar nuclei = 7 cells total, containing 3 + 3 + 2 = 8 nuclei! Match Option (1) in 5 seconds!

1 Monosporic functional megaspore undergoes 3 successive free-nuclear mitotic divisions:

1 \to 2 \to 4 \to 8

nuclei.

2 Cell wall formation organizes 3 cells at chalazal pole (antipodals) and 3 cells at micropylar pole (egg apparatus).

3 The remaining two polar nuclei remain suspended within the shared single large central cell.

4 Total count:

3 + 3 + 1 = 7

cells, containing

3 + 3 + 2 = 8

nuclei.

5 Match Option (1).

🛡️

Why You Can 100% Trust This Shortcut: Canonical NCERT Angiosperm Embryology on Female Gametophyte Development.

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Free Nuclear Mitotic Divisions in Megaspore

The single functional megaspore undergoes three consecutive mitotic nuclear divisions without immediate cytokinesis:

1\text{ Functional Megaspore Nucleus} \xrightarrow{M_1} 2\text{ Nuclei} \xrightarrow{M_2} 4\text{ Nuclei} \xrightarrow{M_3} 8\text{ Free Nuclei}

Step 2

Cell Wall Deposition and Cellular Organization

Cytokinesis and cell wall deposition partition the eight nuclei into specific cellular domains: - Micropylar End (Egg Apparatus): 3 cells total — 1 female gamete (egg cell) and 2 synergids with filiform apparatus. - Chalazal End (Antipodal Cells): 3 distinct uninucleate antipodal cells. - Central Region (Central Cell): 1 very large central cell retaining the 2 remaining polar nuclei.

Step 3

Summation of Cells and Nuclei at Maturity

Summing up the cellular and nuclear inventory at complete maturity:

\begin{aligned} \text{Total Cells} &= 3\text{ (antipodals)} + 3\text{ (egg apparatus)} + 1\text{ (central cell)} = \mathbf{7\text{ cells}} \\[4pt] \text{Total Nuclei} &= 3 + 3 + 2\text{ (polar nuclei)} = \mathbf{8\text{ nuclei}} \end{aligned}

⭐

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

✓ 100% Correct

Verdict & Scientific Reason:

At maturity, 6 nuclei are enclosed by cell walls into discrete single cells, while the central cell contains 2 polar nuclei, yielding 7 cells and 8 nuclei.

💡

Why this is airtight: None. This is the exact textbook definition.

2 2

✗ Incorrect

Verdict & Scientific Reason:

This inverts the numbers; there are 8 nuclei and 7 cells, not 7 nuclei and 8 cells.

⚠️

Student Fallacy (Why candidates pick this trap): Hasty reading under exam pressure leads candidates to transpose "nucleate" and "celled".

3 3

✗ Incorrect

Verdict & Scientific Reason:

False; the central cell contains two free polar nuclei, so there are 8 nuclei in total.

⚠️

Student Fallacy (Why candidates pick this trap): Assuming every individual cell in the embryo sac must strictly contain exactly one nucleus.

4 4

✗ Incorrect

Verdict & Scientific Reason:

False; the two polar nuclei reside together in the same central cell rather than forming two individual cells.

⚠️

Student Fallacy (Why candidates pick this trap): Assuming 8 nuclear divisions inevitably lead to 8 distinct cellular compartmentalizations.

⚠️

NTA Trap Alert: Numerical Inversion of "Nucleate" and "Celled"

NTA places Option (1) as "8-nucleate and 7-celled" and Option (2) as "7-nucleate and 8-celled". Rushing students scan the numbers 7 and 8 without checking which adjective pairs with cells versus nuclei.

🛡️ How to avoid the -1 mark: Always mentally vocalize: "7 cells because central cell is shared; 8 nuclei because central cell has twin polar nuclei".

📖

Core NEET Syllabus Standard

NEET / NCERT Biology · Sexual Reproduction in Flowering Plants Standard Benchmark

Core Scientific Principle Tested:

"A typical mature angiosperm embryo sac is monosporic, 7-celled, and 8-nucleate."

Syllabus Focus: Development of Female Gametophyte (Embryo Sac)

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

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NEET 2021 Botany Question 102 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ "7-Celled, 8-Nucleate" Polygonum Formula

Step-by-Step Rigorous Workflow & Mathematical Proof

Free Nuclear Mitotic Divisions in Megaspore

Cell Wall Deposition and Cellular Organization

Summation of Cells and Nuclei at Maturity

360° Option Elimination Engine Key Feature

NTA Trap Alert: Numerical Inversion of "Nucleate" and "Celled"

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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