Which set of the following organisms multiply by fragmentation?

The correct answer is fungi, filamentous algae, protonema of mosses.

Fragmentation is a form of asexual reproduction in which an organism physically splits or breaks into fragments. Each of these fragments then develops and grows into a mature, fully grown individual that is a clone of the original organism.

Let us analyze the organisms listed in the correct option:
1. Fungi: Many multicellular fungi, such as molds and mushrooms, can easily reproduce when their hyphae (filamentous structures that make up the mycelium) break into pieces. Each piece grows into a new mycelium.
2. Filamentous algae: Algae with thread-like or filamentous structures (such as Spirogyra) reproduce asexually by breaking into smaller filaments or fragments, which then grow through cell division into new filaments.
3. Protonema of mosses: The protonema is a thread-like chain of cells that forms the earliest stage of a moss lifecycle. It is highly filamentous and can easily multiply by fragmentation, where broken parts grow into new protonemata and eventually mature moss plants.

Why other options are incorrect:
- Planaria reproduces primarily by regeneration, while Hydra and Yeast reproduce by budding. Bacteria multiply by binary fission, not fragmentation.
- Amoeba reproduces by binary fission, and viruses do not replicate independently through fragmentation; they require host machinery to replicate.