siliceous cell walls

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Diatoms and silica

Silica is arguably the most important part of diatom biology and ecology. The weight of silica influences the cell's float/sink equilibrium, and influences cell size and accumulation of photosynthetic storage products. Silica also allows for rigid, elaborate cell shapes. Diatom tests are preserved and compacted on the sea floor due to the presence of silica; therefore, it is the key to all the paleontological and industrial uses of diatomaceous earth and deep-sea cores.

In life, diatoms accumulate silica, (SiO₂) as a structural element in their cell walls. The silica need of a diatom may be so great relative to the silica concentration of seawater, that it restricts diatom growth. Furthermore, because solid silica is more dense than seawater, it tends to make diatoms sink into the depths - a true Hades for these organisms, dependent on light in the surface waters for photosynthesis and life.

It is important to realize that silica is one component of a successful organism. Diatoms have evolved a whole host of features that go along with the weight of silica tests to place the cells at the most advantageous position available, both physically in the water and in an evolutionary sense.

Given these limitations, it is perhaps surprising that diatoms have survived evolutionary processes for 100 million years. The limitations of silica might just be a hold-over from their early evolutionary development, a time when conditions in the sea were different or the environment was somehow less selective. But most likely, such limitations may have other very significant advantages that benefit the diatom in life. There has been a great deal of speculation of late as to why diatoms accumulate silica in their cell walls, or from another angle, why a proto-diatom should have been evolutionarily successful.

In reality, the maintenance of a siliceous cell wall is probably due to a combination of some or all of these factors.

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