Draw the diagram of $Spirogyra$ and label the following parts:
$(a)$ Cell wall $(b)$ Pyrenoid $(c)$ Nucleus $(d)$ Chloroplast.

(N/A) The diagram of $Spirogyra$ shows a filamentous green alga with a characteristic spiral-shaped chloroplast.
Key features to label:
$1$. Cell wall: The outermost protective layer of the cell.
$2$. Pyrenoid: Small,proteinaceous bodies embedded within the chloroplast,involved in starch storage.
$3$. Nucleus: The central organelle containing genetic material,usually suspended in the center of the cell by cytoplasmic strands.
$4$. Chloroplast: The ribbon-like,spiral structure responsible for photosynthesis.