Plankton; a diatom frustule

Plankton; colour-enhanced image of a fractured diatom frustule. The frustule is the complex silicon cell wall that acts as a skeleton to support the single-celled diatom. In this image only the frustule and none of the cell contents remain. Diatoms have chloroplasts and can use sunlight to produce food. They are a major component of plankton in both fresh and salt water.