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.
Artificial reefs and reef restoration. What is a reef? For review, a reef is a bar of sand, rock, coral, or similar material lying below the surface of a body of water. Most people immediately think coral reef when they hear the word reef, but there are many other types of reef. The below images show an oyster reef and a coral reef.