Diatom, << DY uh tom, >> is a microscopic, single-celled organism (living thing). Diatoms are found in the ocean, in freshwater lakes, rivers, and streams, and on moist soil. In water, diatoms live attached to rocks, sand, or plants, or they may float freely. Diatoms are probably best known as part of the mass of drifting organisms in oceans called plankton.
Diatoms belong to a group of simple plantlike organisms called algae. Like green plants, diatoms can live and grow using only sunlight, water, carbon dioxide, and certain minerals.
Diatom cells contain both green and yellow-orange pigments that enable them to trap the sun’s energy. This combination of pigments gives diatoms a golden-brown color. For this reason, they are sometimes called golden-brown algae.
Diatoms differ from other algae in that their cells are enclosed in a hard, glasslike shell made of opal. The shell, also called the frustule, consists of two parts that fit one inside the other, like a box with its lid. Most diatoms are either circular or oblong in shape. Diatoms usually multiply through cell division–that is, one cell divides into two cells. After a diatom cell divides, each new cell retains one part of the parent shell and builds a new part to fit into it. Some diatoms stay linked after cell division, forming chain- or ribbon-shaped colonies.
Scientists believe that there are many thousands of species (kinds) of diatoms. Scientists identify species by examining the shells.
Planktonic diatoms are especially plentiful in certain regions of the oceans, where they serve as an important source of food for fish and other marine animals. When diatoms die, their hard shells remain intact. Eventually the shells sink to the bottom of the sea. Over thousands of years, the layer of diatom shells may become very deep. On land, the accumulation of diatom shells from ancient seabeds is mined as diatomaceous earth, also called diatomite. This substance is used as a polishing powder, abrasive, insulator, or filter. It is also used as a filler in paints and in rubber and plastic products.
