Assertion & Reason Test: Animal Kingdom - NEET MCQ

Fishes belonging to class Chondrichthyes have to swim constantly. It is because air bladder is absent in these fishes therefore, they have to swim constantly to avoid sinking.

Echinoderms, such as starfish and sea urchins, indeed exhibit bilateral symmetry during their larval stages but transition to radial symmetry as adults. The reason provided, however, is not correct in this context. Bilateral symmetry is typically associated with mobility and a directed movement, which is beneficial for the larval stages that need to disperse. Sessile organisms, which do not move, often exhibit forms of symmetry that are not necessarily bilateral, as seen in adult echinoderms.

Nematodes, or roundworms, are indeed classified as pseudocoelomates because they possess a body cavity, known as a pseudocoel, which is not completely lined by tissue derived from mesoderm. The reason accurately explains what distinguishes pseudocoelomates from true coelomates, where the latter have a body cavity fully lined with mesoderm. This distinction is important for understanding the evolutionary relationships and functional anatomy of different animal groups.

Flame cells are the excretory organs of Platyhelminthes and other related animals which possess flickering cilia or flagella for driving the excretory products.

Molluscs are indeed known for having a radula, a toothed, chitinous ribbon, which they use for feeding. It acts like a file, scraping or cutting food before ingestion. While the reason correctly describes one function of the radula, it does not encompass all its uses across different mollusc species. The radula's primary function is more general; it is used for feeding, but not all molluscs use it to drill into food sources. Some use it to scrape algae off surfaces, while others may use it in different ways.