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:
http://www.bgsu.edu/departments/biology/facilities/algae/index.html
http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopyuk.org.uk/mag/wimsmall/smal1.html
http://www.euronet.nl/users/janpar/virtual/diatoms.html
http://www.ucl.ac.uk/GeolSci/micropal/diatom.html
http://earthguide.ucsd.edu/diatom/d3a.html