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.
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Endocytosis is a term used to describe a process of active transport that facilitates the movement of particles such as molecules and parts of a cell or the whole cell into a cell.The best scenario for the process occurs when a cell needs to pass/transport molecules that are large and cannot move through the membrane passively.