This false-coloured scanning electron micrograph (SEM) shows a diatom frustule. Diatoms are unicellular organisms and a major group of algae. 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. Diatoms are one of the most common types of phytoplankton, and their communities are often used to measure environmental conditions such as water quality.
How is the frustule formed?
A frustule is composed of two halves, known as thecae. As the diatom divides, each daughter cell retains one theca of the original frustule and produces one new theca. As the diatom prepares to separate, the newly formed nucleus and the pre-existing nucleus each move to the side of the diatom where the new hypotheca (lower half) will be formed. A vesicle known as the silica deposition vesicle forms near the plasma membrane. This forms the centre of the pattern, and silica deposition can continue outward from that point until the frustule is produced.
Why does it look like a radiation symbol?
Anne Weston explains: “In fact, the question here should be ‘Why does a radiation symbol look like a diatom?’ because the diatom would have existed long before the radiation symbol was designed or even thought of! There are thousands of species of diatoms, and this particular type just happens to have this unique and interesting structure.”
The 12th Wellcome Image Awards were announced on 20 June 2012, recognising the creators of the most informative, striking and technically excellent images among recent acquisitions to Wellcome Images, as chosen by a panel of judges.