The cell walls of some are composed of minerals such as calcium carbonate.

I think the correct answer would be algae. The cell walls of some algae are composed of minerals such as calcium carbonate. Algae belongs to the kingdom of protista where most are single celled and found in bodies of water. Most of the cell walls have microfibrils of cellulose and some contains other substances like silica, polysaccharides and calcium carbonate.

The answer would be true. hope this !