Controlled Crystal Symmetry

Biological Strategy

Calcareous sponge

AskNature Team

Image: Dmitry Grigoriev / Shutterstock / CC BY SA - Creative Commons Attribution + ShareAlike

Chemically Assemble Mineral Crystals

The vast majority of biochemical assembly and break down processes––even by the most complex organisms––occur within cells. In fact, cells are able to perform hundreds, even thousands, of chemical transformations at the same time under life-friendly conditions (ambient temperature and pressure in an aqueous environment). Within cells, organisms utilize organic compounds to facilitate the assembly of mineral crystals. For example, oysters utilize acidic proteins and sulfated polysaccharides to assemble layers of aragonite crystals.

Search this Function

Physically Assemble Structure

Living systems use physical materials to create structures to serve as protection, insulation, and other purposes. These structures can be internal (within or attached to the system itself), such as cell membranes, shells, and fur. They can also be external (detached), such as nests, burrows, cocoons, or webs. Because physical materials are limited and the energy required to gather and create new structures is costly, living systems must use both conservatively. Therefore, they optimize the structures’ size, weight, and density. For example, weaver birds use two types of vegetation to create their nests: strong, a few stiff fibers and numerous thin fibers. Combined, they make a strong, yet flexible, nest. An example of an internal structure is a bird’s bone. The bone is comprised of a mineral matrix assembled to create strong cross-supports and a tubular outer surface filled with air to minimize weight.

Search this Function

Modify Solubility (Dissolving, Emulsifying, Precipitating, Crystallizing)

Increasing or decreasing the solubility of chemical constituents is one way of managing a host of metabolic processes including material synthesis. For example, organisms that produce calciferous shells utilize dissolved calcium and carbonate ions, but when the time is right, they raise the pH to create alkaline conditions that trigger calcium carbonate to precipitate out of solution as an insoluble solid.

Search this Function

Chemically Assemble Inorganic Compounds

The vast majority of biochemical assembly and break down processes––even by the most complex organisms––occur within cells. In fact, cells are able to perform hundreds, even thousands, of chemical transformations at the same time under life-friendly conditions (ambient temperature and pressure in an aqueous environment). For example, coral polyps transform dissolved calcium and carbonate ions into crystalized calcium carbonate within the calicoblastic cells.

Search this Function

Sponges

Phylum Porifera (“pore-bearing”): Sponges

Sponges may seem simple, but there’s more to them than meets the eye. True, they don’t have nerves, muscles, or organs. But they do have unique, specialized cells that help them survive. Collar cells have long tails or flagella that line the inner sponge cavity and funnel water through the body. Sponges are filter feeders, taking in large amounts of water and trapping tiny particles to eat. They also have small spiky spicules made of silica or calcium carbonate that help them keep their structure. There are at least 5,000 known species of sponges living in aquatic systems, with 98% of them in the ocean.

Search this Living System

Crystals in glass sponges exhibit controlled growth due to biologically induced reduction in calcitic crystal symmetry.

“Organisms can exert a remarkable degree of control over crystal growth.
One way of achieving this is by the adsorption of specialized
macromolecules on specific planes of the growing crystals. With
continued growth of the crystal, the macromolecules are incorporated
inside the crystal bulk. Their presence does not change the crystal
structure, but creates discontinuities in the perfect lattice. Here we
study in detail three unusual cases of reduction in symmetry at the
level of crystal domain shapes, induced by this controlled
intercalation. We examined sponge spicules, which are single crystals
of Mg-bearing calcite. They were specifically chosen for this study,
because their morphologies do not reflect the hexagonal symmetry of
calcite. Their crystal textures (coherence lengths and angular spreads)
were characterized by high-resolution X-ray diffraction with
well-collimated synchrotron radiation. The results are compared to
analogous studies of synthetic calcite and Mg-bearing calcite. In all
the selected spicules reduction in symmetry is observed in the
coherence lengths among symmetry-related crystallographic directions.
The reconstructed shapes of the domains of perfect structure closely
match the specific spicule morphologies. The synthetic crystals show no
such reduction in symmetry. Although the manner by which such exquisite
control is achieved is not known, we envisage it involving a
combination of oriented nucleation with either physical or
stereochemically driven adsorption.”(Aizenberg et al. 1995:414)

Last Updated August 18, 2016

References

Journal article

Biologically Induced Reduction in Symmetry: A Study of Crystal Texture of Calcitic Sponge Spicules

Chemistry - A European Journal | 20/07/2007 | Joanna Aizenberg, Jonathan Hanson, Thomas F. Koetzle, Leslie Leiserowitz, Stephen Weiner, Lia Addadi

embedly preview

AskNature