Diatoms Eukaryotic algae Common type of phytoplankton Unicellular or colonies Primary producers in the food chain Over 200 genera of living diatoms, and approximately 100,000 species Found in freshwater and marine environments

Diatom cells are contained within a unique silica cell wall called frustules, comprising two separate shells –two shells overlap one other like the two halves of a petri dish Silica is made in the cell and then extruded to the cell exterior and added to the wall.

Reproduction When a diatom divides to produce two daughter cells, each cell keeps one of the two halves and grows a smaller half within it. After each division cycle the average size of diatom cells in the population gets smaller. When a certain minimum size is reached, they reverse this decline by expanding in size to give rise to a much larger cell –Caused by sexual reproduction.

Ecology Diatoms produce an estimated 20% to 25% photosynthesis on the planet A major food resource for marine and freshwater microorganisms and animal larvae A major source of atmospheric oxygen.

Nanotechnology The deposition of silica by diatoms may also prove to be of utility to nanotechnology Diatom cells manufacture different shapes and sizes, potentially allowing diatoms to manufacture micro- or nano-scale structures which may be of use in a range of devices, including drug delivery