In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.

When it interacts with ryanodine receptors, this element upregulates its own release, and this compound forms the cell plates of coccolithophores. Stimulation of Gq ("g-sub-q") opens a channel that allows for this ion's movement, and proteins that bind this ion have an EF hand motif. Cellular concentrations of this ion are regulated by IP3. Parafollicular cells of the (*) thyroid produce a compound that reduces the concentration of this ion in blood, and its intestinal absorption requires vitamin D. This ion interacts with Troponin to stimulate muscle contraction, and the lumens of sarcoplasmic reticula have high concentrations of this ion. For 10 points, name this divalent cation that is stored in bones.
Science

Lin and Shu proposed the density-wave theory to explain how the structure of these entities is sustained. The most accurate method for measuring the distances to distant ones uses a relation between their maximum rotational velocity and absolute magnitude, which is known as the Tully-Fisher method. They are generally blue because of their high content of old stars, and one type of them features arms that emanate from each end of a namesake structure. They have discs like the lenticular type, but contain much more angular momentum than the elliptical type. FTP name these galaxies, some of which are barred, including the Milky Way.
Science

A poem by this man claims that the title object is "a resounding haven where in great waves / My soul can drink the scent." This poet claims that the only thing "more ugly, more wicked, more filthy" than "crawling monsters" is ennui [ahn-wee] in a poem that calls the reader a hypocrite. This poet of "The Head of Hair" described a figure that will "nonchalantly chaperone a ship / across the bitter fathoms of the sea". A collection by this poet of "To the Reader" contains one poem that begins "Old Pluvius, month of rains" and another that begins "When the low heavy sky weighs like a lid", both of which are titled "Spleen". Name this poet whose work "The Albatross" is found, like all of his poems, in Les Fleurs du Mal [lay floor du mahl], or The Flowers of Evil.
Literature