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Question #46863
The Question
Hemichordates, representing an evolutionary bridge among deuterostomes, utilize diffuse myoepithelial arrangements for movement. In contrast, true chordates exhibit highly organized skeletal muscle striation patterns. Which of the following molecular or structural adaptations was primarily responsible for establishing this definitive sarcomeric organization during evolution?
Options
- A.
The de novo emergence of actin and myosin as contractile proteins to replace primitive ciliary tubulin.
- B.
The spatial organization of thin filaments into parallel arrays anchored by specialized Z-disc proteins such as alpha-actinin.
- C.
The substitution of calmodulin with troponin as the primary calcium-binding sensor located within the sarcoplasmic reticulum.
- D.
The fusion of diffuse myoepithelial cells to form a functional syncytium that completely lacks a specialized sarcolemma.
Check Your Answer
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
Skeletal Muscle Striation Pattern|Hemichordata Evolutionary Link|Myoepithelial Cells
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Distinguishing between the mere presence of contractile proteins and their complex spatial organization.
Students often mistakenly believe that primitive organisms lack actin/myosin (Option A) or fall for location traps regarding regulatory proteins (Option C).
The core NCERT concept tested is that the Z-line is the structural anchor for actin, and its biochemical evolution (alpha-actinin) is what physically creates the striated sarcomeric pattern.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Structural Organisation in Animals - Class 11 |
| Concept | Skeletal Muscle Striation Pattern |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |