'Pond silk' is the common name of

Q. 'Pond silk' is the common name of

1. Spongilla
2. Chlorella
3. Gorallina
4. Spirogyra
5. Selaginella

Answer: Spirogyra
Q. Spirogyra is called pond silk because

1. Filaments are made up of silk 
2. Filaments are slippery to touch and shining 
3. Both (1) and (2) 
4. None of the above 

Answer: 2.Filaments are slippery to touch and shining

Spirogyra

Spirogyra, (genus Spirogyra), any member of a genus of some 400 species of free-floating green algae (division Chlorophyta) found in freshwater environments around the world. Named for their beautiful spiral chloroplasts, spirogyras are filamentous algae that consist of thin unbranched chains of cylindrical cells. They can form masses that float near the surface of streams and ponds, buoyed by oxygen bubbles released during photosynthesis. They are commonly used in laboratory demonstrations.

Spirogyra forms silk like layer on the water. It is present in an abundant amount on the freshwater bodies or slow running water. They are slippery in nature, so are commonly known as pond silk or water silk.

Spirogyra (common names include water silk, mermaid's tresses, and blanket weed) is a genus of filamentous charophyte green algae of the order Zygnematales, named for the helical or spiral arrangement of the chloroplasts that is characteristic of the genus. It is commonly found in freshwater habitats, and there are more than 400 species of Spirogyra in the world. Spirogyra measures approximately 10 to 100 μm in width and may grow to several centimeters in length.

Spirogyra is very common in relatively clean eutrophic water, developing slimy filamentous green masses. In spring Spirogyra grows under water, but when there is enough sunlight and warmth they produce large amounts of oxygen, adhering as bubbles between the tangled filaments. The filamentous masses come to the surface and become visible as slimy green mats. Spirogyra has a cell wall, nucleus, pyrenoid and spiral chloroplasts. It is very rare among the plant-like protists.