(i) Regeneration:
Regeneration is the process by which an organism can re-grow a complete individual from its cut or broken body parts. Organisms like Planaria can regenerate — if cut into pieces, each piece grows into a complete new organism.
Organism that does not show regeneration: A dog (or any complex multicellular organism).
Reason: In complex organisms, cells are highly specialised and organised into tissues and organs placed at definite positions in the body. Such a highly organised system cannot simply regenerate from an isolated cell or body part.
(ii) The dark green filamentous structures are Spirogyra. It reproduces by fragmentation.
Process: Upon maturation, the Spirogyra filament simply breaks up into smaller pieces or fragments. Each fragment then grows and develops into a new complete Spirogyra filament. This occurs because Spirogyra has a simple body organisation where each fragment retains the capacity to grow into a new individual.
Source: Chapter 7 — How do Organisms Reproduce?, Section 7.2.2 Fragmentation
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