Answers and bookmarks are saved in this browser, across visits. They do not sync to your account.
Q241.
Assertion (A): Chondrichthyes have a cartilaginous endoskeleton.
Reason (R): Their notochord is persistent throughout life.
[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 correct features of Chondrichthyes. However, the persistence of the notochord is a separate primitive trait and not the reason for the endoskeleton being cartilaginous.
Q242.
Assertion (A): Sharks must swim constantly to avoid sinking.
Reason (R): They lack an air bladder.
[Animal-Kingdom] [class-xi]
Correct option: A [ ]
Remark: Both A and R are true and R is the correct explanation of A. Explanation: The air bladder provides buoyancy in bony fish. Since sharks lack this organ, they must keep swimming to generate lift and prevent sinking.
Q243.
Assertion (A): The teeth of sharks are modified placoid scales.
Reason (R): The skin of Chondrichthyes is tough and contains minute placoid scales.
[Animal-Kingdom] [class-xi]
Correct option: A [ ]
Remark: Both A and R are true and R is the correct explanation of A. Explanation: The teeth in sharks are structurally homologous to the placoid scales covering their skin; they are essentially modified, enlarged placoid scales.
Q244.
Assertion (A): Some cartilaginous fish like Torpedo have electric organs.
Reason (R): Chondrichthyes are warm-blooded (homoiothermous) animals.
[Animal-Kingdom] [class-xi]
Correct option: C [ ]
Remark: A is true but R is false. Explanation: Some cartilaginous fishes (e.g., Torpedo) have electric organs (true). The reason is false; Chondrichthyes are poikilothermous (cold-blooded).
Q245.
Assertion (A): Osteichthyes includes fishes with a bony endoskeleton.
Reason (R): They possess an air bladder which regulates buoyancy.
[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 correct features of Osteichthyes. The presence of an air bladder is an important feature, but it doesn't explain why their skeleton is bony.
Q246.
Assertion (A): In bony fishes, gills are covered by an operculum.
Reason (R): In cartilaginous fishes, gill slits are separate and without an operculum.
[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 descriptions of bony and cartilaginous fishes, respectively. They are contrasting features but one does not explain the other.
Q247.
Assertion (A): Amphibians can live in both aquatic and terrestrial habitats.
Reason (R): The name Amphibia indicates a dual life.
[Animal-Kingdom] [class-xi]
Correct option: A [ ]
Remark: Both A and R are true and R is the correct explanation of A. Explanation: The name Amphibia (Amphi: dual, bios: life) literally means 'dual life,' referring to their ability to inhabit both aquatic and terrestrial environments.
Q248.
Assertion (A): Amphibians have a three-chambered heart.
Reason (R): Their heart has two auricles and one ventricle.
[Animal-Kingdom] [class-xi]
Correct option: A [ ]
Remark: Both A and R are true and R is the correct explanation of A. Explanation: The amphibian heart is described as three-chambered because it is composed of two auricles and one ventricle.
Q249.
Assertion (A): The skin of amphibians is moist and without scales.
Reason (R): Respiration in amphibians can occur through gills, lungs, and skin.
[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 correct features of amphibians. The moist, scaleless skin facilitates cutaneous (skin) respiration, but the reason also lists other modes (gills, lungs), making it a related but not a direct explanation.
Q250.
Assertion (A): In amphibians, the alimentary, urinary, and reproductive tracts open into a common cloaca.
Reason (R): Fertilisation in amphibians is internal and development is direct.
[Animal-Kingdom] [class-xi]
Correct option: C [ ]
Remark: A is true but R is false. Explanation: Assertion is correct. The reason is false; fertilisation in amphibians is typically external, and development is indirect (involving a larval stage).