Amylases are enzymes within bacteria that break down the polysaccharide starch into the monosaccharide glucose. Starch is an abundant carbon supply in nature, but it is too large to pass through bacterial semipermeable membranes. Some bacteria use amylase hydrolysis as a means of breaking down the polysaccharide starch into monosaccharides and disaccharides capable of transcending the cell membrane. Once inside the cell, these sugars are degraded by by microbial enzymes, releasing carbon and energy. Once an unknown bacterium is isolated and diluted in liquified agar medium, starch degradation by amylase can be ascertained. Using aseptic technique, starch agar plates are inocculated with bacteria by scratching the inocculating needle across the plate. After an incubation time of 48 hours, the plate is flooded with iodine. Iodine changes color from a deep purple to brown in the presence of starch. Clear areas around growth indicate the use of amylase enzymes to utilize the polysaccharide starch, a positive amylase test. Absence of a clear area means that the bacteria was not able to break down the large starch molecules, and lack of growth indicates microbial starvation.