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Q281.
Assertion (A): The mantle cavity in molluscs contains feather-like gills.
Reason (R): These gills have respiratory and excretory functions.
[Animal-Kingdom] [class-xi]
Correct option: A [ ]
Remark: Both A and R are true and R is the correct explanation of A. Explanation: Feather-like ctenidia in the mantle cavity serve respiration (and in some cases are involved in excretion/contact with coelomic fluids), so the reason supports the assertion.
Q282.
Assertion (A): Chordates possess a post-anal tail.
Reason (R): A post-anal tail is absent in non-chordates.
[Animal-Kingdom] [class-xi]
Correct option: A [ ]
Remark: Both A and R are true and R is the correct explanation of A. Explanation: A post-anal tail is a defining chordate feature absent in non-chordates.
Q283.
Assertion (A): Vertebrates have kidneys for excretion and osmoregulation.
Reason (R): They possess a ventral muscular heart with two, three, or four chambers.
[Animal-Kingdom] [class-xi]
Correct option: B [ ]
Remark: Both A and R are true but R is not the correct explanation of A. Explanation: Both are true vertebrate features, but the circulatory/heart condition does not explain kidney presence.
Q284.
Assertion (A): Hagfish (Myxine) belongs to the class Chondrichthyes.
Reason (R): It has a cartilaginous endoskeleton.
[Animal-Kingdom] [class-xi]
Correct option: D [ ]
Remark: Assertion (A) is false but R is true. Explanation: Hagfish (Myxine) is not a chondrichthyan; it is a cyclostome (Class Cyclostomata). The reason is true about cartilaginous skeletons but doesn't classify Myxine correctly.
Q285.
Assertion (A): Trygon (Sting ray) possesses a poison sting.
Reason (R): It belongs to the class Osteichthyes.
[Animal-Kingdom] [class-xi]
Correct option: C [ ]
Remark: A is true but R is false. Explanation: Trygon (a stingray) may possess a venomous spine, but rays are cartilaginous fishes (Class Chondrichthyes), not Osteichthyes.
Q286.
Assertion (A): The skin of Osteichthyes is covered with cycloid or ctenoid scales.
Reason (R): The skin of Chondrichthyes is covered with placoid scales.
[Animal-Kingdom] [class-xi]
Correct option: B [ ]
Remark: Both A and R are true but R is not the correct explanation of A. Explanation: Both statements correctly describe scale types in bony and cartilaginous fishes; one does not explain the other.
Q287.
Assertion (A): In amphibians, a tympanum represents the ear.
Reason (R): They do not have external ear openings like reptiles.
[Animal-Kingdom] [class-xi]
Correct option: B [ ]
Remark: Both A and R are true but R is not the correct explanation of A. Explanation: Amphibians have tympanic membranes (tympana) for hearing; some amphibians lack external pinnae but the presence/absence of external ears varies and the reason does not fully explain the assertion.
Q288.
Assertion (A): The hind limbs of birds are modified for various functions like walking, swimming, or clasping.
Reason (R): The forelimbs of birds are modified into wings.
[Animal-Kingdom] [class-xi]
Correct option: B [ ]
Remark: Both A and R are true but R is not the correct explanation of A. Explanation: Both statements describe different limb adaptations in birds; forelimb modification into wings is separate from hind limb specialization..
Q289.
Assertion (A): All viviparous animals are mammals.
Reason (R): Some sharks are viviparous.
[Animal-Kingdom] [class-xi]
Correct option: D [ ]
Remark: Assertion (A) is false but R is true. Explanation: Viviparity occurs outside mammals as well — e.g., some sharks — so the assertion is false; the reason provides a correct counterexample.
Q290.
Assertion (A): All triploblastic animals are coelomates.
Reason (R): Platyhelminthes are triploblastic but acoelomate.
[Animal-Kingdom] [class-xi]
Correct option: D [ ]
Remark: Assertion (A) is false but R is true. Explanation: Not all triploblastic animals have a true coelom — platyhelminths are triploblastic acoelomates, demonstrating the assertion is false.