Rough Draft of Diatom Lesson Script
1. Diatoms are plant life. They are a kind of single cell, eukaryotic photosynthetic algae. Diatoms are found in almost every aquatic environment on Earth. They are plentiful in the ocean, ponds, lakes, rivers, swamps, and even moist soils. Any where there is moisture, there are sure to be diatoms.
2. Diatoms have a hard, durable skeleton made of silica, or silicon, called a frustule. Diatoms are nnon-motil, meaning they do not move on their own, but depend on the action of waves, current, upwellings, and other hydrodynamic forces for movement. Some species of diatoms can creep along by using a form of slug-like locomotion, secreting a mucus-like substance from a groove, or raphe, on their underside.
3. Because they are photosynthetic, they live in waters that allow for the penetration of light. Diatoms are rarely found below 600 feet. This is called the photic zone, or the area where there is enough lightfor plants to carry out photosynthesis.
4. Diatoms are tiny. Most range from 20 to 200 mircons in length or diameter. The largest diatoms are only 2 millimeters long.
5. Most diatoms live solitary lives, floating along, tossed by wind and wave, using the energy in sunlight to drive their metabolic processes. Some are colonial, attaching themselves to one another by mucous-like filaments, not unlike a spider’s web.
6. Diatoms can exist in large numbers, so large that sediments found at the bottom of some bodies of water are made up of nothing but the shells, or frustules, of dead diatoms.
7. These sediments can be mined for use in tootpaste, paints, and filtering materials (like diatomaceous earth, used in pool filters) .
8. The first known examples of diatoms are from the Jurassic Period, from about 200 to 145 million years ago, however ,scientists believe diatoms existed before this time, they just have not yet been discovered.
9. The oldest well preserved diatoms are from the Cretaceous Period, form about 145 to 65 million years ago. Because there are so many different forms of diatoms dated in these two eras, scientists believe diatoms have a long evolutionary history .
10. Diatoms are divided up into two orders; Centrales and Pennales.
11. The face of the diatom frustules, or shells, are covered with pores, processes, spines, hyaine areas, and other distinct features. It is these structures that are used to classify diatoms.
12. The long history of ditoms make them useful in many areas of paleological study. Paleoceanography, in particular, makes use of diatoms for determining or extraploating a wide variety of data.
13. Because diatoms have very speficic environmental tolerances; certain species live within certain parameters in terms of salinity, temperature, deoth, light conditions, etc. These characteristics are used to created paleoreconstructions of environments long vanished.
14. Diatoms have been studied since the late eighteenth century, however the first real advances in the field came in the early nineteenth century when diatoms came under the lenses of the much improved tools of the time.
15. The study of diatoms is a branch of phycology, and phycologists specializing in diatoms are called diatomists.
16. Diatoms have been well studied both in their natural habitat and in cultures by biologists and there is therefore a wealth of knowledge on their biology and ecology.
17. Diatoms are easily prepared for veiwing using a light microscope. Wet samples can be smeared onto a slide for immediate examination.
18. Plant matter may obscure detail of the frustule so this is removed using hydrogen peroxide.
19. A small amount of hydrochloric acid may be added to remove any calcium carbonate and the sample is then rinsed in distilled water.
20. The sample is then dilluted and spread onto coverslips, dried and mounted on slides. Because the refractive indices of water and silica are very similar, a mounting medium with a higher refractive index is used in order to increase the contrast.
21. The living tissue of diatoms consists of a cytoplasmic layer that lines the interior of the frustule and surrounds a large central vacuole, within the cytoplasmic layer there is a diploid nucleus and several pigment-bearing plastids (the site of photosyntheseis).
22. The diatom frustule is often compared to a pill-box with a larger upper valve, or shell, called the epitheca and a smaller lower valve, known as the hypotheca.
23. Many diatoms hve shells that are different, top and bottom. This is called heterovalvate. This is most obvious in Achnanthaceae diatoms, where one shell half has a raphe, or large groove used in locomotion, and the other does not,
24. When a diatom cell divides, each new cell takes its epitheca from the valve of the parent frustule, and within ten to twenty minutes builds its own hypotheca; this process may occur between one and eight times per day.
25. How fast diatoms reproduce depends in part on how much dissolved silica there is in the water. This also affect how how large diatoms can grow.
26. Recently, diatoms have come to the attention of scientists trying to develop new types of nanotechnology.
27. Diatom nanotechnology, a new interdisciplinary area, has spawned collaborations in biology, biochemistry, biotechnology, physics, chemistry, material science and engineering.
28. Diatom cells repeatedly and reliably manufacture valves of shapes and sizes, potentially allowing diatoms to manufacture micro- or nano-scale structures which may be of use in a range of devices, including: optical systems, semiconductor nanolithography; and even using diatom valves as vehicles for drug delivery.
29. Diatoms that produce shells of particular shapes and sizes could be artificially evolved in the laboratory, and then used in cultures to mass produce nanoscale components.
30. Recent progress in diatom based nanotechnology research include advances in biomineralization, biophotonics, photoluminescence, microfluidics, compustat domestication, multiscale porosity, silica sequestering of proteins, detection of trace gases, controlled drug delivery and computer design.
31. Diatoms might be the first organisms that fulfill the promise of a wide scale, organic, commercial production of nanotechnology.
32. In addition to fulfilling a critical role in the web of life on the planet, acting as a kind of paloloogical recording device, having commerical value, and offering great promise for nanotechnologies, diatoms are also, quite simply, beautiful.
33. Their frustules come in a variety of shapes and sizes, and their skeletal structures have inspired sculptors, photographers, and other artists to create works based on their fantastic forms.
34. To learn more about diatoms visit these sites: