Which is the dominant and active phase in the alternation of generations in algae?

In $Chlorophyceae$,sexual reproduction occurs by .............

Sexual reproduction in $Spirogyra$ involves the fusion of:

Phycology is the study of

$A$: Pyrenoids may or may not be surrounded by a sheath of starch plates in algae.
$R$: In higher plants,these are replaced by amyloplasts.

The algal cell wall is composed of