Q.25 Botany ⭐ 360° Option Elimination Active

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NEET 2020 Botany Question 25 Solution

Topic: Structural Organisation in Animals · Official NTA Booklet Code E1

Question

If the head of cockroach is removed, it may live for few days because:

(1)the supra-oesophageal ganglia of the cockroach are situated in ventral part of abdomen.
(2)the cockroach does not have nervous system.
(3)the head holds a small proportion of a nervous system while the rest is situated along the ventral part of its body.
(4)the head holds a 1/3rd of a nervous system while the rest is situated along the dorsal part of its body.

✓

Verified Against NTA Final Answer Key

Option (3) : the head holds a small proportion of a nervous system while the rest is situated along the ventral part of its body.

📚 Structural Organisation in Animals Easy

📋 Given Parameters & Problem Setup

Organism Cockroach (Periplaneta americana)

Phenomenon Decapitated cockroach survives for several days to a week

Question Objective Identify the anatomical neural explanation

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The 30-Second Exam Hall Shortcut: ⚡ "Cockroach Head Holds Little Brain; Most Ganglia Lie Ventrally in Thorax & Abdomen!"

⏱️ Save ~20 seconds

The nervous system of the cockroach is decentralized: the head contains only a bit of nervous tissue (supra-oesophageal ganglion), while the vast majority comprises 9 segmental ganglia arranged along a double ventral nerve cord. Thus, removing the head leaves basic reflex control intact! Select Option (3).

1 Recall NCERT statement on cockroach nervous system: - The nervous system of cockroach is spread throughout the body. - The head holds a bit of a nervous system while the rest is situated along the ventral part of its body. - So, now you understand why if the head of a cockroach is cut off, it will still live for as long as one week.

2 Check nerve cord position: Ventral, solid, double (NOT dorsal!). Eliminates Option (4).

3 Check Option (3): Matches verbatim NCERT explanation.

4 Select Option (3).

🛡️

Why You Can 100% Trust This Shortcut: NCERT Biology · Structural Organisation in Animals (Cockroach Nervous System: The head holds a bit of a nervous system while the rest is situated along the ventral part of its body. So, if the head of a cockroach is cut off, it will still live for as long as one week).

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Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Anatomy of the Cockroach Nervous System

The nervous system of *Periplaneta americana* is segmental and decentralized: - Head Region: The cephalic region contains the supra-oesophageal ganglion (cerebral ganglion / "brain"), which supplies sensory nerves strictly to the antennae and compound eyes. It represents only a tiny fraction of the total central nervous system. - Body Trunk: The rest of the central nervous system consists of a double, solid ventral nerve cord carrying 9 segmental ganglia: - 3 large ganglia in the thorax (pro-, meso-, and meta-thoracic ganglia controlling legs and wings). - 6 ganglia in the abdomen coordinating autonomic segmental and reproductive reflexes.

\textbf{Cockroach Nervous System} \implies \begin{cases} \mathbf{Head:} & \text{Minor proportion (Supra-oesophageal ganglion)} \\[4pt] \mathbf{Ventral\,Trunk:} & 3 \text{ Thoracic} + 6 \text{ Abdominal Ganglia } [\mathbf{Majority\,of\,Control}] \end{cases}

Step 2

Physiological Basis of Prolonged Decapitated Survival

Because respiration occurs passively via segmental lateral spiracles and trachea (independent of head or mouth breathing), and because locomotion and visceral tone are controlled by thoracic and abdominal ganglia along the ventral nerve cord, a decapitated cockroach can survive for up to a week until it ultimately dies of dehydration or starvation.

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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. The supra-oesophageal ganglion is located in the head above the oesophagus, not in the abdomen.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing cranial supra-oesophageal ganglion with abdominal ganglia.

2 B

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Arthropods possess a sophisticated, well-developed nervous system.

⚠️

Student Fallacy (Why candidates pick this trap): Assuming primitive invertebrates lack nervous systems.

3 C

✓ 100% Correct

Verdict & Scientific Reason:

Correct. Verbatim NCERT explanation for the prolonged survival of a decapitated cockroach.

💡

Why this is airtight: None. Direct recall of standard cockroach physiology.

4 D

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Non-chordates possess a VENTRAL nerve cord, not dorsal.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing the chordate dorsal nerve cord with the invertebrate ventral nerve cord.

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NTA Trap Alert: Dorsal vs Ventral Nerve Cord Inversion Trap

Option 4 attempts to trap candidates by claiming the nerve cord lies along the *dorsal* part of the body. Chordates have dorsal hollow nerve cords; Non-chordates (like cockroaches) have ventral solid double nerve cords.

🛡️ How to avoid the -1 mark: Remember: Invertebrates/Cockroach = Ventral nerve cord.

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Core NEET Syllabus Standard

NEET / NCERT Biology · Structural Organisation in Animals Standard Benchmark

Core Scientific Principle Tested:

"The head holds a small proportion of the nervous system while the major portion lies along the ventral part of the body."

Syllabus Focus: Cockroach Nervous System

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

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NEET 2020 Botany Question 25 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ "Cockroach Head Holds Little Brain; Most Ganglia Lie Ventrally in Thorax & Abdomen!"

Step-by-Step Rigorous Workflow & Mathematical Proof

Anatomy of the Cockroach Nervous System

Physiological Basis of Prolonged Decapitated Survival

360° Option Elimination Engine Key Feature

NTA Trap Alert: Dorsal vs Ventral Nerve Cord Inversion Trap

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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