Answer A:
1. Spiral chloroplast:
This organelle help in photosynthesis, because it contain green pigment called chlorophyll in which water and carbon dioxide combine in the presences of sun light to prepare glucose.
2. Cell wall:
It is chemically composed of an outer layer of pectin and an inner layer of cellulose. It provide rigidity and shape to spirogyra cell.
Answer B:
The other parts which are not labelled include mucilage, cytoplasm, pyrenoids, cytoplasmic strand.
Answer C:
Function of pyrenoid:
Each chloroplast strand has several round bodies called 'pyrenoids', which are responsible for starch production.
Function of mucilage:
Mucilage help in retaining water in cell.