Calcium is a chemical element with symbol Ca and atomic number 20. Calcium is a soft gray Group 2 alkaline earth metal, fifth-most-abundant element by mass in the Earth's crust. The ion Ca2+ is also the fifth-most-abundant dissolved ion in seawater by both molarity and mass, after sodium, chloride, magnesium, and sulfate.[5] Free calcium metal is too reactive to occur in nature. Calcium is produced in supernova nucleosynthesis.
In biochemistry, two biopolymers are antiparallel if<span> they run </span>parallel<span> to each other but with opposite alignments. An example is the two complementary strands of a </span>DNA<span>double helix, which run in opposite directions alongside each other.</span>
It provided people with 1 of their most basic needs, a dependable supply of food
