Diatom frustule Anne Weston, LRI, CRUKIt looks a radioactive hazard warning. In fact, this delicate assembly of triangles is a scanning electron micrograph of a diatom. Diatoms are single-cell organisms that are one of the most common types of phytoplanktons and play a major role in sustaining life on Earth. Although usually too small to be seen with the naked, phytoplankton form green blooms on the sea and convert sunlight and carbon dioxide into oxygen. They also provide food for a large number of aquatic species. Diatoms are encased within a hard cell wall made from silica, which is known as a frustule and is composed of two halves. Frustules have a variety of patterns, pores, spines and ridges, which are used to determine genera and species. The health of communities of phytoplankton is measured carefully by scientists because they provide useful indications of environmental conditions such as water quality

Photograph: Wellcome Images