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Q261.
Assertion (A): Phylum Ctenophora reproduces only by sexual means.
Reason (R): In ctenophores, sexes are not separate, and fertilisation is external.
[Animal-Kingdom] [class-xi]
Correct option: A [ ]
Remark: Both A and R are true and R is the correct explanation of A. Explanation: Many ctenophores reproduce sexually; sexes are not always separate (some are hermaphrodite) and fertilisation is typically external.
Q262.
Assertion (A): Some members of Platyhelminthes like Planaria possess high regeneration capacity.
Reason (R): They are exclusively endoparasites.
[Animal-Kingdom] [class-xi]
Correct option: C [ ]
Remark: A is true but R is false. Explanation: Planaria have remarkable regenerative ability and are free-living (not exclusively endoparasites).
Q263.
Assertion (A): A closed circulatory system is present in Annelida.
Reason (R): Blood is circulated through a series of vessels of varying diameters.
[Animal-Kingdom] [class-xi]
Correct option: A [ ]
Remark: Both A and R are true and R is the correct explanation of A. Explanation: Annelids have a closed circulatory system where blood flows through vessels.
Q264.
Assertion (A): Limulus (King crab) is called a living fossil.
Reason (R): It is a gregarious pest.
[Animal-Kingdom] [class-xi]
Correct option: C [ ]
Remark: A is true but R is false. Explanation: Limulus (horseshoe crab) is called a living fossil due to its ancient lineage; the reason claiming it is a gregarious pest is incorrect.
Q265.
Assertion (A): The body of a mollusc is unsegmented.
Reason (R): The body of an annelid shows metameric segmentation.
[Animal-Kingdom] [class-xi]
Correct option: A [ ]
Remark: Both A and R are true and R is the correct explanation of A. Explanation: Molluscs are generally unsegmented; annelids show clear metamerism — contrasting features.
Q266.
Assertion (A): The excretory organ in Hemichordata is the proboscis gland.
Reason (R): Hemichordates have an open type circulatory system.
[Animal-Kingdom] [class-xi]
Correct option: B [ ]
Remark: Both A and R are true but R is not the correct explanation of A. Explanation: The statements are facts about hemichordates; the circulatory type does not explain the excretory organ identity.
Q267.
Assertion (A): In chordates, the heart is ventral.
Reason (R): In non-chordates, the heart, if present, is dorsal.
[Animal-Kingdom] [class-xi]
Correct option: A [ ]
Remark: Both A and R are true and R is the correct explanation of A. Explanation: A ventral heart is typical of chordates, contrasting with dorsal hearts of many non-chordates.
Q268.
Assertion (A): Gnathostomata is a division of vertebrates that bears jaws.
Reason (R): Gnathostomata includes superclasses Pisces and Tetrapoda.
[Animal-Kingdom] [class-xi]
Correct option: A [ ]
Remark: Both A and R are true and R is the correct explanation of A. Explanation: Gnathostomata comprises jawed vertebrates including fishes (pisces) and tetrapods.
Q269.
Assertion (A): Members of Chondrichthyes are viviparous.
Reason (R): Males possess claspers on their pelvic fins for internal fertilisation.
[Animal-Kingdom] [class-xi]
Correct option: B [ ]
Remark: Both A and R are true but R is not the correct explanation of A. Explanation: Some chondrichthyans are viviparous and males use claspers; however the presence of claspers facilitates internal fertilisation but does not mean all members are viviparous.
Q270.
Assertion (A): Osteichthyes are mostly oviparous.
Reason (R): Fertilisation in bony fishes is usually external.
[Animal-Kingdom] [class-xi]
Correct option: A [ ]
Remark: Both A and R are true and R is the correct explanation of A. Explanation: Most bony fishes lay eggs and external fertilisation is common, explaining oviparity.