CBSE Class 10 Science 2022 · Paper 31/1/1 · Question 4

Planaria reproduces by regeneration. Planaria is a multicellular animal with a fully differentiated body, with a distinct head and tail. If its body is cut into pieces, specialised cells in each piece multiply and form a mass of cells, and these cells change into the various kinds of cells and tissues in an organised sequence, so each piece rebuilds the parts it has lost and grows into a complete Planaria. Spirogyra does not do this: it is a simple filament of similar cells that, on maturing, just breaks into pieces, each of which grows by cell division into a new filament. That is fragmentation, not regeneration. Another organism that reproduces by regeneration: Hydra.