CBSE Class 10 Science 2020 · Paper 31/C/1 · Question 27(a)

(a) (i) No. The eyes of Planaria, insects, octopus and vertebrates do the same job, detecting light, but their structure is very different (simple eye-spots in Planaria, compound eyes in insects, camera-like eyes built differently in the octopus and in vertebrates). They are analogous organs that arose separately, not homologous organs inherited from a common ancestor, so they cannot establish a common evolutionary origin. (ii) No. Organisms are grouped by characteristics inherited from a common ancestor. The eyes evolved separately, so grouping by them would bring together unrelated animals: a flatworm (Planaria), arthropods (insects), a mollusc (octopus) and chordates (vertebrates). (b) Fossils show that some dinosaurs, which were reptiles, had feathers although they could not fly with them; birds later adapted feathers for flight, so birds are very closely related to reptiles. Fossils of Archaeopteryx show feathers and wings like a bird together with teeth, clawed fingers and a long bony tail like a reptile, a connecting link between the two groups. Birds also still have scales on their legs and lay shelled eggs, as reptiles do.