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In biology, a test is the hard shell of some spherical marine animals and protists, notably sea urchins and microorganisms such as testate foraminiferans, radiolarians, and testate amoebae. The term is also applied to the covering of scale insects. The related Latin term testa is used for the hard seed coat of plant seeds.
The BMC shell appears icosahedral [26] or quasi-icosahedral, and is formed by (pseudo)hexameric and pentameric protein subunits. [27] Structures of intact shells have been determined for three functionally distinct: BMC types, carboxysomes, [28] the GRM2 organelles involved in choline catabolism [29] and a metabolosome of unknown function.
These shells, often called tests, can be single-chambered or have multiple interconnected chambers; the cellular machinery is contained within the shell. So important is the test to the biology of foraminifera that it provides the scientific name of the group— foraminifera , Latin for "hole bearers", referring to the pores connecting chambers ...
In other fields, the term "artificial cell" can refer to any compartment that somewhat resembles a biological cell in size or structure, but is synthetically made, or even fully made from non-biological components. The term "artificial cell" is also used for structures with direct applications such as compartments for drug delivery.
Foraminifera typically produce a test, or shell, which can have either one or multiple chambers, some becoming quite elaborate in structure. [8] These shells are commonly made of calcium carbonate (CaCO 3) or agglutinated sediment particles. Over 50,000 species are recognized, both living (6,700–10,000) [9] [10] and fossil (40,000).
The shells have small pores that allow for gas exchange and nutrient uptake. Coccolithophores and foraminifera also have hard protective shells, but the shells are made of calcium carbonate. These shells can help with buoyancy, allowing the organisms to float in the water column and move around more easily.
The molluscs are calcareous organisms, as are the calcareous sponges , that have spicules which are made of calcium carbonate. [1] Additionally, reef-building corals, or Scleractinia, are calcareous organisms that form their rigid skeletal structure through the precipitation of aragonite (i.e., a polymorph of calcium carbonate). [2]
The mollusc shell is a biogenic composite material that has been the subject of much interest in materials science because of its unusual properties and its model character for biomineralization. Molluscan shells consist of 95–99% calcium carbonate by weight, while an organic component makes up the remaining 1–5%.