Which substance is most likely to increase in the rods of the retina when the light is turned on?

Photons activate rhodopsin to become metarhodopsin II in the rods of the retina, which means that exposure to light decreases the concentration of rhodopsin and increases the concentration of metarhodopsin II, also called activated rhodopsin. Metarhodopsin II leads to a decrease in cGMP through a series of biochemical reactions cAMP levels are unchanged. Vitamin A levels are not likely to change with exposure to light