Body Segmentation in Animal Kingdom — NEET Biology
📚 Practice ConceptSegmentation in the body is first observed in which of the following:
Which of the following statements regarding reproduction and development across early animal phyla (Porifera, Cnidaria, Ctenophora) are NOT correct? S1: Sponges are typically monoecious, producing both eggs and sperms, and exhibit internal fertilisation. S2: Metagenesis, an alternation of generations, is observed in some cnidarians where polyps produce medusae asexually and medusae form polyps sexually. S3: Ctenophores are exclusively dioecious with external fertilisation and direct development, exhibiting bioluminescence. S4: In Porifera, asexual reproduction mainly occurs through fragmentation, and their development involves a morphologically distinct larval stage. S5: Both Cnidarians and Ctenophores are characterized by the absence of larval stages, indicating direct development in these phyla.
View solution & NCERT explanation
Correct answer: B — S3 and S5 only
The question asks to identify incorrect statements concerning reproduction and development in Porifera, Cnidaria, and Ctenophora. S1: Correct. For Porifera, NCERT states, "Sexes are not separate (hermaphrodite), i.e., eggs and sperms are produced by the same individual. Fertilisation is internal..." (4.2.1). S2: Correct. For Cnidaria, NCERT states, "polyps produce medusae asexually and medusae form the polyps sexually (e.g., Obelia)." This accurately describes metagenesis (4.2.2). S3: Incorrect. For Ctenophora, NCERT states, "Sexes are not separate" (meaning monoecious, not dioecious). Also, "Fertilisation is external with indirect development" (not direct development). "Bioluminescence... is well-marked in ctenophores." (4.2.3). S4: Correct. For Porifera, NCERT states, "Sponges reproduce asexually by fragmentation... development is indirect having a larval stage which is morphologically distinct from the adult." (4.2.1). S5: Incorrect. For Ctenophores, NCERT explicitly states "Development is indirect" (4.2.3), which implies the presence of larval stages. Therefore, the statement claiming absence of larval stages and direct development for both is false. Statements S3 and S5 are NOT correct. Option B correctly identifies these incorrect statements. Options A, C, and D are incorrect as they misidentify correct statements or fail to include all incorrect ones. The core concept tested is the comparative understanding of reproductive strategies and developmental patterns in primitive animal phyla.
What does NCERT say about Segmentation body first observed?
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