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Question #47436
The Question
The evolutionary transition from a diffuse nerve net in Cnidarians to a highly centralized nervous system in vertebrates involved overcoming a 'delay bottleneck' in impulse transmission. Which of the following statements regarding this evolutionary trend and neural conduction is INCORRECT?
Options
- A.
In primitive invertebrates, the absence of myelin and reliance on numerous chemical synapses create a significant delay in overall neural response time.
- B.
To increase conduction velocity without myelination, some invertebrates evolved giant axons, which reduce internal resistance but physically restrict high-density cephalization.
- C.
The myelin sheath in vertebrates acts as an insulator that decreases ion leakage, allowing continuous and uniform depolarization along the entire length of the axon.
- D.
The centralization of the nervous system in higher vertebrates relies on myelinated fibers to maintain rapid conduction velocities despite having densely packed, small-diameter neurons.
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Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Evolutionary_Exception
Tackle problems where standard rules evolve or change based on specific environmental constraints.
Concepts Behind This Question
Synaptic Delay Determinant|Evolutionary Chronology|Ganglia vs Central Nervous System
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often know that myelin 'speeds up' conduction but misunderstand the exact mechanism.
The trap relies on the phrase 'continuous and uniform depolarization', which sounds like an efficient, positive trait, but actually describes the slower mechanism of unmyelinated fibers.
The question tests the synthesis of NCERT Neural Control (saltatory conduction) with Evolutionary Biology (cephalization constraints).
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Neural Control and Coordination - Class 11 |
| Concept | Synaptic Delay Determinant |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |