The chloroplast of $Chlamydomonas$ is . . . . . . .

$A$ : Sexual reproduction shows considerable variation in the type and formation of sex cells in members of $Chlorophyceae$.
$R$ : It may be isogamous,anisogamous and oogamous.

Identify the given figures of algae and select the correct option.

Which of the following produces isogamous and non-flagellated gametes?

Assertion : Red algae contribute to the production of coral reefs.
Reason : Some red algae secrete and deposit calcium carbonate over their walls.

In $Spirogyra$,meiosis occurs in