Definition. The normal concentration of sodium in the blood plasma is 136-145 mM. Hyponatremia occurs when sodium falls below 130 mM. Plasma sodium levels of 125 mM or less are dangerous and can result in seizures and coma. Description. Sodium is an atom, or ion, that carries a single positive charge.
reef1. 1  a ridge of rocks or sand, often of coral debris, at or near the surface of the water. 2  Mining. a lode or vein.
A coral reef is made of thin layers of calcium carbonate. Coral polyps form a living mat over a calcium carbonate skeleton. Stony corals (or scleractinians) are the corals primarily responsible for laying the foundations of, and building up, reef structures.Massive reef structures are formed when each individual stony coral organismâor polypâsecretes a skeleton of calcium carbonate.Most stony corals have very small polyps, averaging one to three millimeters (0.04 to 0.12 inches) in diameter, but entire colonies can grow very large and weigh several tons.assive reef structures are formed when each individual stony coral organismâor polypâsecretes a skeleton of calcium carbonate. Most stony corals have very small polyps, averaging one to three millimeters (0.04 to 0.12 inches) in diameter, but entire colonies can grow very large and weigh several tons.