The element silicon (Si) is used by all living organisms either in molecular processes or in the formation of the mineral silica. The mineral is found in single cell organisms (e.g. radiolarian, diatoms, dinoflagellates and algae) through molluscs (e.g. limpets) to higher plants and primitive animals such as sponges. It is formed from an environment that is undersaturated with respect to Si and under conditions of around neutral pH and low temperature, c. 4–40°C. The mineral can be formed both intra‐ or extracellularly and specific biochemicals involved with mineral deposition include lipids, proteins (including heavily posttranslationally modified proteins), long‐change polyamines and carbohydrates. Knowledge of the complete genome for some species is providing opportunities to uncover the precise mechanisms of element uptake, transport and deposition although much still remains to be understood.

Key Concepts:

  • Silicon is an essential element for many if not all organisms.

  • A range of biomolecules/biopolymers are used to control and regulate silica precipitation in the natural environment.

  • The presence of biogenic silica in an organism confers functional properties on that organism which may include structural/mechanical support and/or defence against biotic or abiotic environmental stresses.

  • Much remains to be understood in respect of how the element is transported, concentrated and spatially organised within organisms as well as the effect the presence of the element/mineral has on other cellular functions.

Keywords: silica; silicic acid; opal; biosilicification; silicatein; long chain polyamines; silaffin; secondary plant cell wall; diatoms; sponges

Figure 1.

Radiolarians. In comparison with organisms such as diatoms and choanoflagellates, much less is known concerning the formation of the skeletons of these organisms as they are much more difficult to culture in the laboratory. Organisms may be up to many hundreds of micrometres in diameter. Reproduced with the permission of the publisher from Haeckel E (1974) Art Forms in Nature. New York: Dover Publications. Originally published by Ernst Haeckel in Kunstformen der Natur (1899–1904).

Figure 2.

Sponge spicules. (a) Plagiotriaene, Geodia gibberosa Lamarck (length of spicule 850 μm). (b) Anamonaene, Tetilla sp. (length 620 μm). (c) Clad of same (width 4.3 μm). (d) Phyllotriaene, Racodiscula sp. (length 270 μm). (e) Protriaene, Tetilla sp. (thickness of main shaft 1.3 μm). (f) Dichotriaene, Penares sp. (across spicule 520 μm). (g) Triactine, Plakina sp. (each spine 20 μm in length). (h) Calthorps, Plakina sp. (spine length 43 μm). (i) Anatriaene, Tetilla serica (Lebwohl) (spicule thickness 4.3 μm). Note: cross‐sections of many sponge spicules show a central axial channel containing silicatein with the silica arranged in bands.

Figure 3.

Plant silica examples. (a) Silica cells from rice (Oryza sativa), 7 μm in diameter. (b) Silicified cell wall stomatal structures from the branches of Equisetum arvense (scale bar 20 μm). (c) Silica found inside the stem of Equisetum arvense (scale bar 100 nm).



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Perry CC (2003) Silicification: the processes by which organisms capture and mineralize silica. Reviews in Mineralogy and Geochemistry 54: 291–327.

Perry CC and Keeling‐Tucker T (2000) Biosilicification: the role of the organic matrix in structure control. Journal of Biological Inorganic Chemistry 5: 537–550.

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Perry, Carole C(May 2010) Silica. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0002079.pub2]