Ulothrix is

Which of the following statements are applicable to brown algae?
$(I)$ They contain pigments like chlorophyll $a$,chlorophyll $c$,carotenoids,and xanthophylls.
$(II)$ They vary in color from olive green to various shades of brown.
$(III)$ Food is stored as complex carbohydrates,in the form of laminarin or mannitol.
$(IV)$ The cell wall is composed of cellulose and algin.
$(V)$ The cell wall is covered on the outside by a gelatinous coating of algin.

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

What type of life cycle is observed in the algae shown in the figure?

$100$ zygospores,alternating with empty cells in Spirogyra,are formed under ................. conjugation and the total number of daughter filaments formed will be ..........................

In Thallophyta,embryo formation does not occur because: