Multicellular green algae
Most multicellular green algae of fresh water are simple or branched filaments; as they grow, their cells divide continuously and the thallus keeps enlarging. Ulothrix grows attached to stones and wood in rivers and streams: its body is an unbranched thread, a single row of chain-like cells; one cell at the base is a rhizoid that holds it to the object; the other green cells have a belt-shaped chromatophore. In asexual reproduction a cell divides into 4 or 8 parts that leave as zoospores swimming with four flagella, then attach to something, divide crosswise and form a new thread. In sexual reproduction two-flagellate sex cells of equal size (isogametes) fuse in pairs to form a zygote; the zygote gets a thick wall and rests, then divides into four cells, each of which becomes a new thread. Spirogyra forms unbranched threads of large cylindrical cells in ponds and slow water and floats freely without attaching. Cladophora has a branched thallus up to 1 m long; Chara is a much-branched alga 30–60 cm tall found in ditches, ponds and rice fields. The algae of Uzbekistan were studied in depth by Academician A. M. Muzaffarov. Algae enrich water with oxygen and are food for fish.
| Alga | Body | Size, habitat |
|---|---|---|
| Ulothrix | unbranched thread | rivers and streams |
| Spirogyra | unbranched thread, large cylindrical cells | ponds and slow water |
| Chara | much branched | 30–60 cm; ditches, ponds, rice fields |
Under the microscope: make a slide from a filamentous alga (Spirogyra or Cladophora) from a pond or aquarium, look for the row of cells, chromatophore and nucleus and draw them. Safety: collect water only with adults; do not touch blue-green “bloomed” water; wash hands with soap; handle slides carefully.