Grade 11 : Biology - Animal Kingdom (Set 3)

Explanation: Choanocytes (collar cells) line the spongocoel and canals of sponges (Phylum Porifera). Their flagellar movement drives water through ostia into the spongocoel and out through the osculum, assisting in nutrition and respiration.

Explanation: Cnidarians displaying polymorphism like Obelia undergo metagenesis. Polyps produce medusae asexually (by budding), and medusae produce polyps sexually (by gamete fusion).

Explanation: Ctenophores (comb jellies) are exclusively marine, radially symmetrical, diploblastic organisms possessing eight external rows of ciliated comb plates for locomotion, and exhibiting bioluminescence.

Explanation: Platyhelminthes (flatworms like Fasciola) are dorso-ventrally flattened acoelomates. They possess specialized cells called flame cells (protonephridia) for osmoregulation and excretion.

Explanation: Aschelminthes are pseudocoelomate. The body cavity is not lined by mesoderm; instead, mesoderm is present as scattered pouches in between the ectoderm and endoderm.

Explanation: Nereis is an aquatic annelid possessing lateral unjointed appendages called parapodia, which assist in swimming and gaseous exchange.

Explanation: Arthropods feature a chitinous exoskeleton, jointed appendages (arthros = joint, poda = appendages), triploblastic coelomate body, and an open circulatory system.

Explanation: The mouth of many molluscs contains a file-like rasping organ for feeding called the radula.

Explanation: Adult echinoderms exhibit radial symmetry (usually pentamerous), while their free-swimming larvae display bilateral symmetry.

Explanation: Hemichordates like Balanoglossus and Saccoglossus have a cylindrical body composed of an anterior proboscis, a collar, and a long trunk. Excretion is carried out by the proboscis gland located in the proboscis region.

Explanation: Branchiostoma is a cephalochordate (Chordata), so it possesses all primary chordate characters: dorsal hollow nerve cord, notochord, and pharyngeal gill slits. The other options are non-chordates.

Explanation: Cyclostomes (e.g., Petromyzon) are jawless vertebrates (Agnatha). They have a sucking and circular mouth, lack paired fins and scales, are ectoparasites, and undergo anadromous migration to freshwater for spawning, dying shortly after.

Explanation: Cartilaginous fishes (Chondrichthyes) lack a swim bladder (air bladder), which regulates buoyancy in bony fishes. Hence, they must swim continuously to avoid sinking.

Explanation: Class Osteichthyes includes bony fishes characterized by a bony endoskeleton, terminal mouth, 4 pairs of gills covered by an operculum, cycloid/ctenoid scales, and presence of an air bladder.

Explanation: In Class Amphibia, the digestive, excretory, and reproductive tracts open into a shared chamber called the cloaca, which opens to the exterior.

Explanation: Most reptiles have a 3-chambered heart (two atria, one incompletely divided ventricle). However, crocodilians (like Crocodilus and Alligator) possess a fully 4-chambered heart.

Explanation: Avian adaptations for flight include pneumatic (hollow) long bones to reduce mass, modification of forelimbs into wings, and air sacs connected to lungs for efficient supplementary respiration.

Explanation: While almost all mammals are viviparous, Ornithorhynchus (platypus) is an exception—an oviparous (egg-laying) mammal that possesses hair and functional mammary glands.

Explanation: Platyhelminthes are acoelomate (no coelom). Aschelminthes are pseudocoelomate (false coelom). Annelida onwards (Annelida, Arthropoda, Mollusca, Echinodermata, Hemichordata, Chordata) are true coelomates.

Explanation: Subphylum Urochordata has a notochord restricted to the larval tail stage (retrogressive metamorphosis in adults like Ascidia). Subphylum Cephalochordata (e.g., Branchiostoma) has a notochord extending from head to tail, remaining persistent throughout life. Both statements are correct.