photosynthesis

Photosynthesis is the process plants use in order to make food from sunlight, carbon dioxide, and water. Chlorophyll in the leaves is most responsible for this process. In the spring and summer months, the chlorophyll is abundant and gives the leaves their green color. In the fall, the days become shorter and shorter and the UV index generally decreases. This causes the chlorophyll to decrease in number and therefore the green color fades. The fading of the green color allows other colors to apear on the leaves like yellow and orange, which are caused by different pigments in the leaf. Once winter rolls around, ther temerature, UV index, and daylight hours are too low for the leaves to survive so they die and fall off of the trees.