1. A single-celled aquatic alga with a hard silica shell, found in freshwater and marine environments.
Usage: biology; commonly studied in schools

Examples

• Diatoms are microscopic organisms that form the base of many aquatic food chains.
• Under a microscope, the intricate glass-like shells of diatoms are beautiful to observe.
• Diatoms produce about half of the oxygen in Earth's atmosphere.
• Scientists use diatoms to assess water quality in lakes and rivers.
• The fossilized shells of ancient diatoms form deposits called diatomaceous earth.
• Diatoms contain chlorophyll and perform photosynthesis to produce their own food.