The mitochondria is believed to be important in controlling the supply of oxygen available for making light in fireflies. An increased rate of respiration decreases the intracellular oxygen concentration which reduces the amount available for light production. The mitochondria of the photocyte exists near the perimeter of the cell while the peroxisome is typically found closer to the middle of the cell. It is worth noting that not all bioluminescence in the firefly light organ occurs in the granules of the photocyte. Some fluorescent protein has been found to exist in the posterior region of the organ.