What biological function requires magnesium?

In plants Magnesium (Mg) is the central element in chlorophyll (the green pigment in plants). The chlorophyll molecule has a Magnesium ion electrically bounded in its center. Magnesium is responsible for the production of sugar in plants during the Photosynthesis and also for the transport of sugar for use by plant.

Answer: The biological function that requires Magnesium is the process that uses Sunlight to produce sugar in plants, or Photosynthesis.