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Marine Botany
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Monterey
Bay Flora
Methods PHYCOLOGICAL SOCIETY OF AMERICA |
Diatoms and DragDrag is any force that acts in a direction opposite the direction of motion. In other words, drag forces slow things down. This is true for the space shuttle entering out atmosphere, your car when you let off the accelerator, and diatoms sinking in the oceanic water column. In still seawater, diatoms sink because of their heavy silica tests. But they can't sink forever, because if they fall below the critical depth, they won't survive. The cells rely on turbulent eddies to elevate them near the surface again. We can imagine a timer starting every time a diatom returns to the surface: it has to catch another upward minicurrent before time, or sunlight, runs out. Drag forces are very important to diatoms because they slow down the cells' sinking speed. By increasing the drag force it feels, a diatom can stay above the critical depth longer; it gets more time on its clock. Drag forces also let diatoms ride father when upbound currents hit them. Drag cells are increased whenever cells increase their surface area. Many morphological features of diatoms, including cell shape and areolae, increase drag. Setae are a great way to keep afloat, because they increase surface area so much and they aren't very heavy. Even forming colonies with other cells, increasing the surface area of the whole group, may help to keep diatoms in sunlit surface waters. Photo Gallery
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