what is meant by filaments of spirogyra?what is pectin?

Filaments of spirogyra means that Spirogyra exists in the form of long filaments.

Spirogyra is unbranched with cellular cells connected end to end in long green filaments.

Pectin is a polysaccharide found naturally in plant cell walls. It is used by plants as a cementing material between cells. It is extracted from the cell walls of plants, especially of fruits.

(Under acidic conditions it forms a gel. It is often used in processed foods, especially jellies and jams where it causes thickening.)