Leaves are one of the places where plants build up starch to store energy. After removing a leaf and boiling it in alcohol to clear the green color, you add potassium iodide drops to reveal how much starch is inside. The darker the purple color, the more starch the leaf contains.

Photosynthesis uses carbon dioxide to build sugar and starch inside leaves — but does more carbon dioxide mean more starch? This experiment tests that link by sealing geranium plants in bags with different carbon dioxide levels. After a day in sunlight, you boil each leaf in alcohol to remove the green color, then add potassium iodide drops. The darker the purple, the more starch the leaf contains.

Plants pull carbon dioxide from the air and turn it into starch through photosynthesis. One experiment seals geranium plants in bags with different carbon dioxide levels to measure starch production. The leaf from the high-carbon-dioxide bag produces the darkest purple color when tested, showing it built the most starch.