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Unformatted text preview: (SiO 2 ). The diatom cell wall is perforated by numerous small openings. When diatoms reproduce asexually, each received one old valve. The new valve fits inside the old one; therefore, the new diatom is smaller than the original one. Once the shells reach a certain size the diatom reproduces sexually and restores its size, allowing the asexual reproduction cycle to begin anew. Diatoms secrete a silicon dioxide shell (called a frustule) that forms the fossil deposits known as diatomaceous earth , which is used in filters and as abrasives in polishing compounds. Diatoms divide into two groups,the pennaleans with bilateral symmetry and elongated shape, and another, the centraleans, with radial symmetry and a rotund shape. Certain diatoms also are important indicators of water quality, while others are useful fossils for age-dating Quaternary deposits. ....
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- Fall '10
- Biology, Diatom, diatoms, numerous unicellular algae