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Phylum Chrysophyta - (SiO 2 The diatom cell wall is...

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Phylum Chrysophyta This group of freshwater, marine, and terrestrial algae includes the golden algae. Although most members of this group are autotrophs, the vast majority of them can become heterotrophs when light levels are low. Food is stored as oils, and photosynthetic pigments include chlorophyll a and c and yellow carotenoid pigments. This phylum includes several distinct groups, some of which may be removed to other phyla in the future, such as the silicoflagellates and yellow-green algae. Phylum Bacillarophyta: Diatoms live in glass houses Some classifications include this phylum in the chrysophytes. Diatoms are the most numerous unicellular algae in the oceans. They are extremely numerous and an important source of food and O 2 for heterotrophs in aquatic systems. Examples of the various types of diatoms are shown in Figure 20. Diatoms have a cell wall comnprised of two halves technically referred to as valves. These valves are mostly made of silica
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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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Phylum Chrysophyta - (SiO 2 The diatom cell wall is...

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