|
|
|
| Current Issue |
|
|
| Resources |
|
|
|
The Littlest Greenhouse
| Article
# : |
16972 |
|
|
Section : |
NATURAL SCIENCE
|
| Issue
Date : |
4 / 1990 |
1,293 Words |
| Author
: |
Rex L. Lowe
Rex L. Lowe is professor of biology at Bowling Green State
University in Ohio. HIs research centers on the ecology of
diatoms. |
Plant? Animal? Or animated crystal? Diatoms - minute, single-celled jewels of the microbial world - posed and intriguing puzzle to early microscopists. In nearly every aquatic habitat that early explorers of things microbial examined with their compound light microscopes, they discovered a seemingly endless variety of organisms that did not seem to fit into the rigid nineteenth-century classifications of life. Although they possessed chlorophyll and a definite cell wall similar to plants, this wall was glassy and transparent. As many appeared to "crawl" about, they were initially classified as animals.
However, we should not be too harsh on early microscopists' judgment. It is difficult to discard ideas confirmed by centuries of observations in a world without microscopes. Modern schools of thought have either considered diatoms primitive, single-celled plants or put them into a kingdom known as Protista - a classification that serves as an "orphanage" for single-celled organisms that do not fit easily into the plant or animal kingdom.
Glass Jewels
Just why are diatoms and enigma to taxonomists? The most strikingly obvious trait exclusively shared by all diatoms is the nature of the cell wall, which is composed almost entirely of silicon dioxide, essentially glass. Like glass, it is colorless and transparent, allowing sunlight to stream into the cell. The cell wall of the diatom consists of two overlapping halves, mimicking a tiny glass box with a tight fitting lid. With its chloroplasts inside, the diatom cell is very much like a unicellular greenhouse.
Any child who has ever collected insects or tadpoles knows that living things cannot survive in a glass jar for very long unless holes are punched in the lid of that jar. All living things require exchange of gases and nutrients with the environment, and so it is with the diatoms living inside their minute glass cases. The diatom cell wall is adorned with numerous pits and pores that allow the living cell contents to interrelate with the environment. As sunlight streams through the transparent cell wall, nutrients diffuse through the pores and gases such as oxygen seep out. The distribution of the pores on the cell wall is very symmetric and pleasing to the human eye, and is specific for each species of diatom. In concert with the pleasing shapes of these glass "jewels," the symmetry of their ornamentation renders them among the most stunningly beautiful organisms under the
...
Read Full Article
Look for this article in Ask.com
|
|
