Question

Which is pond scum?
(a)Spirogyra
(b)Ulothrix
(c)Anabaena
(d)Nostoc

Answer 1

Hint: In stagnant waters, pond scum is a mass of intertwined filaments of algae or cyanobacteria. Pond scum is a free-floating freshwater alga found on the surface of stagnant pools, ponds, and ditches, etc. It is popularly referred to as water silk or pond silk.

Complete answer:
Pond scum is a large growth of algae or other stagnant water sources on the surface of the pond. Owing to the green compound present that aids in photosynthesis, these pigments are called chlorophyll. They are autotrophic in nature.
Spirogyra is known as pond scum, since large masses float on the surface of the filaments. It is often referred to as pond silk because, by dissolving pectin from the outer layer of the cell wall, which is glossy and slimy silk, it continuously secretes mucilage.

Additional Information: Spirogyra is a filament that is unbranched. The cells are all identical and grouped in a single row. The cells are cylindrical, wide, and long. There are two layers of the cell wall; the outer layer is of pectic material and the cellulose inner layer. Cytoplasm, which covers a large central vacuole, is present inside the cell. In the center of the cell, there is a large single nucleus present. Cytoplasmic strands carry the nucleus. The most feature characteristic of the cell is the spirally arranged ribbon or strap-shaped chloroplasts. The chloroplast count ranges from 1 to 16. There are several chloroplast pyrenoids present.
So, the correct answer is, ‘Spirogyra’.

Note: Owing to their bright green silky appearance, spirogyra is widely known as pond silk, water silk, pond scum, or mermaid's plants. In wide free-floating submerged mats, rivers, ditches, and slow-flowing streams, it is a single-cell freshwater alga that occurs.