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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.
For example, in carboxysomes, ribulose-1,5-bisphosphate, bicarbonate, and phosphoglycerate must cross the shell, while carbon dioxide and oxygen diffusion is apparently limited. [ 50 ] [ 51 ] Similarly, for the PDU BMC, the shell must be permeable to propanediol, propanol, propionyl-phosphate, and potentially also vitamin B12, but it is clear ...
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 of the shell in the multi-chambered species. Foraminiferal tests are usually made of calcite, a form of calcium carbonate (CaCO
Foraminifera (/ f ə ˌ r æ m ə ˈ n ɪ f ə r ə / fə-RAM-ə-NIH-fə-rə; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of Rhizarian protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly an external shell (called a "test") of diverse forms and materials.
The biogenic formation of calcium carbonate structures is the result of a combination of biological and physical processes such as genetics, cellular activity, crystal competition, growth in confined spaces, and self-organization processes. The composition of these structures, and the mechanisms involved in building them, are highly diverse.
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]
Protists such as diatoms and radiolaria have intricate, glass-like shells made of silica that are hard and protective, and serve as a barrier to prevent water loss. 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 ...
The soluble component of the shell matrix acts to inhibit crystallization when in its soluble form, but when it attaches to an insoluble substrate, it permits the nucleation of crystals. By switching from a dissolved to an attached form and back again, the proteins can produce bursts of growth, producing the brick-wall structure of the shell. [2]
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