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Question #46113
The Question
While studying the evolutionary constraints of animal body plans, a student notes that diploblastic organisms (e.g., Hydra) rely entirely on simple diffusion for excretion, whereas the first triploblastic organisms (e.g., Fasciola) possess specialized excretory structures called protonephridia. What is the primary embryological reason diploblastic animals cannot develop complex excretory organs like protonephridia?
Options
- A.
The mesoglea acts as a highly rigid, impermeable barrier that prevents the invagination of ectodermal cells to form excretory ducts.
- B.
Protonephridia and their supporting parenchymal tissues are mesodermal derivatives, and diploblasts lack the mesoderm required for such organ-level organization.
- C.
The development of specialized excretory organs strictly requires a fluid-filled coelomic cavity lined by mesoderm, which diploblasts lack.
- D.
In diploblasts, the endoderm is exclusively modified into a gastrovascular cavity, leaving no germ layer available to form a closed excretory system.
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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
Cnidaria|Ctenophora|Mesoglea|Diploblastic Exception
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often conflate the requirement of a 'mesoderm' with the requirement of a 'coelom'.
The trap (Option C) exploits this by suggesting a coelom is needed for excretory organs.
However, Platyhelminthes (flatworms) prove that mesoderm alone (forming parenchyma and flame cells) is sufficient for organ-level excretion, even without a coelom.
Diploblasts lack both, but the 'hard limit' for organogenesis is the absence of the mesoderm itself.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Animal Kingdom - Class 11 |
| Concept | Diploblastic Exception |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |