The group listed here that contains silica in its surface covering is the:
ciliates
red algae
diatoms
water molds

The group that contains silica the diatoms.  Diatoms are unicellular algae. They have a silica based cell wall known as a frustule, which gives each diatom a particular shape.

Diatoms exist as single cells  though some maybe found in colonies that create beautiful shapes which can be leaf - shaped, oval, round and other shapes.

The outer shells of diatoms are used in industry in the manufacture of many products such as toothpaste. The gritty texture in toothpaste is due to addition of diatoms .

a axis of a graph is a color or shade so we can all go outside and have a party so we can eat   some grilled cheese sammiches and broccoli and have some ugly fun times

i don't know why i put this, i know its not the i was just bored : p

delete this answer while you can

true is the final answer!