Final answer:
The assertion that diatoms have cell walls made of silicon dioxide is true. Their unique silica-based cell walls differ significantly from the mostly organic polysaccharide-based cell walls found in other organisms.
Step-by-step explanation:
Are Diatom Cell Walls Made of Silicon Dioxide?
The statement that diatoms are unicellular algae that possess a cell wall made of silicon dioxide is true. Diatoms are indeed a fascinating group of unicellular photosynthetic algae, renowned for their unique cell walls which are composed of silica dioxide, similar to the composition of glass or quartz. These cell walls, which are also referred to as frustules, consist of two distinct halves that overlap like a shoebox and its lid. Diatoms exist primarily as individual cells, though some form colonies, and their structure allows them to float in the upper layers of water bodies to access sunlight for photosynthesis.
Unlike the majority of organisms which have cell walls made up of organic polysaccharides, the diatom's use of silica dioxide is relatively rare in biological terms. The intricately patterned and resistant nature of these silica shells contributes to their role in the sediment of aquatic environments after the diatom's death. Diatoms also require selenium and silica, elements which are not commonly needed by most plants or organisms.