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Q271.
Assertion (A): Ichthyophis is a limbless amphibian.
Reason (R): Most amphibians have two pairs of limbs.
[Animal-Kingdom] [class-xi]
Correct option: B [ ]
Remark: Both A and R are true but R is not the correct explanation of A. Explanation: Ichthyophis (a caecilian) is limbless while most amphibians have two pairs of limbs; the general fact does not explain the exception.
Q272.
Assertion (A): Snakes and lizards shed their scales as skin cast.
Reason (R): The body of reptiles is covered by dry and cornified skin and epidermal scales.
[Animal-Kingdom] [class-xi]
Correct option: A [ ]
Remark: Both A and R are true and R is the correct explanation of A. Explanation: Reptilian skin is dry and cornified with scales which are periodically shed as the animal grows.
Q273.
Assertion (A): All birds can fly.
Reason (R): Flightless birds like the Ostrich exist.
[Animal-Kingdom] [class-xi]
Correct option: D [ ]
Remark: Assertion (A) is false but R is true. Explanation: The assertion that all birds fly is false; ostriches and other flightless birds are examples — the reason correctly states that flightless birds exist.
Q274.
Assertion (A): Mammals are found in a variety of habitats.
Reason (R): Some mammals have adapted to fly or live in water.
[Animal-Kingdom] [class-xi]
Correct option: A [ ]
Remark: Both A and R are true and R is the correct explanation of A. Explanation: Mammals occupy diverse habitats because different species evolved specialized adaptations, like flight (bats) or aquatic life (whales).
Q275.
Assertion (A): The organ systems in different animal groups exhibit the same patterns of complexities.
Reason (R): Organ systems are associations of organs for a specific physiological function.
[Animal-Kingdom] [class-xi]
Correct option: D [ ]
Remark: Assertion (A) is false but R is true. Explanation: Organ systems are defined as associations of organs for a function (true). Different animal groups show varying complexities (so A is false).
Q276.
Assertion (A): Sponges are primitive multicellular animals.
Reason (R): They have a cellular level of organisation.
[Animal-Kingdom] [class-xi]
Correct option: A [ ]
Remark: Both A and R are true and R is the correct explanation of A. Explanation: Sponges are primitive and exhibit cellular-level organisation which underlies their simplicity.
Q277.
Assertion (A): Sponges are hermaphrodites.
Reason (R): Eggs and sperms are produced by different individuals.
[Animal-Kingdom] [class-xi]
Correct option: C [ ]
Remark: A is true but R is false. Explanation: Many sponges are hermaphrodites (produce both gametes), but the reason is false because eggs and sperms are produced by the same individual in hermaphrodites, not by different individuals.
Q278.
Assertion (A): Corals have a skeleton composed of calcium carbonate.
Reason (R): Corals belong to the Phylum Porifera.
[Animal-Kingdom] [class-xi]
Correct option: C [ ]
Remark: A is true but R is false. Explanation: Corals secrete calcium carbonate skeletons but they belong to Phylum Cnidaria (Coelenterata), not Porifera.
Q279.
Assertion (A): Nereis is a dioecious annelid.
Reason (R): Earthworms and leeches are monoecious.
[Animal-Kingdom] [class-xi]
Correct option: A [ ]
Remark: Both A and R are true and R is the correct explanation of A. Explanation: Many polychaetes like Nereis are dioecious, while oligochaetes such as earthworms and many leeches are monoecious.
Q280.
Assertion (A): Arthropods possess sensory organs like antennae and eyes.
Reason (R): Statocysts or balancing organs are also present in arthropods.
[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 are true sensory features of arthropods; the second statement lists additional sensory/balance organs but doesn't explain the first.