Sexual reproduction in $Spirogyra$ can be described as:

Presence of a basal rhizoidal cell in $Ulothrix$ is an example of:

Which type of sexual reproduction is found in $Spirogyra$?

Consider the following statements:
$I$. They reproduce asexually by non-motile spores and sexually by non-motile gametes.
$II$. In this class,sexual reproduction is oogamous and accompanied by complex post-fertilisation developments.
$III$. The common members are $Polysiphonia$,$Porphyra$,$Gracilaria$ and $Gelidium$.
The above characteristics belong to which class of algae?

$A$ : In $Volvox$,heterogametes are formed in the sexual life cycle.
$R$ : Non-motile gametes are transferred by water.

Which is the dominant phase in the life cycle of algae?