Q.59 During gastrulation in Xenopus frog, the blastocoel
1. becomes the gut
2. is filled with endodermal cells and disappears
3. is filled with mesoderm and disappears
4. is displaced, and its original location becomes an endoderm lined cavity.
Xenopus Gastrulation: Blastocoel Fate Revealed
Option 4 correctly states that during Xenopus frog gastrulation, the blastocoel is displaced, and its original location becomes an endoderm-lined cavity.
Gastrulation Process Overview
Xenopus gastrulation transforms blastula into trilaminar gastrula via involution at dorsal blastopore lip, forming ectoderm, mesoderm, endoderm.
Fluid-filled blastocoel (animal pole cavity) shifts as mesendoderm involutes vegetally, creating archenteron.
Bottle cells initiate invagination; convergent extension elongates embryo while displacing original blastocoel space.
Correct Answer: Option 4
Blastocoel displaced, original location becomes endoderm-lined cavity—archenteron roof (endoderm) occupies former blastocoel position.
| Option | Statement | Accuracy |
|---|---|---|
| 1 | Becomes the gut | Wrong—gut forms from archenteron, not blastocoel |
| 2 | Filled with endodermal cells, disappears | Wrong—endoderm lines cavity, doesn’t fill/displace it |
| 3 | Filled with mesoderm, disappears | Wrong—mesoderm involutes through blastopore, doesn’t fill blastocoel |
| 4 | Displaced; original site endoderm-lined | Correct—standard Xenopus fate map |
Detailed Option Breakdown
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Option 1 (Incorrect): Gut derives from archenteron (invaginated endoderm); blastocoel fluid cavity doesn’t persist as gut lumen.
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Option 2 (Incorrect): Endoderm precursors involute vegetally; blastocoel roof receives migrating head mesoderm, not endodermal filling.
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Option 3 (Incorrect): Mesoderm migrates along blastocoel roof (sub-blastocoelic), doesn’t fill cavity—fills space between ecto/endoderm.
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Option 4 (Correct): Classic description—blastocoel shrinks/roof collapses as involuting cells displace it; endoderm lines prospective gut cavity.
Visualized Movement
Blastula: Animal cap (ectoderm) | BLASTOCOEL | Vegetal endoderm
Gastrula: Ectoderm epiboly → ← Mesendoderm involution
Original blastocoel site → ENDODERM-LINED ARCHENTERON
Essential NEET concept: blastocoel fate distinguishes amphibian gastrulation from mammalian implantation.
