Leaf
A leaf is a plant's principal organ of photosynthesis, the process by which sunlight is used to form foods from carbon dioxide and water. Leaves also help in the process of transpiration, or the loss of water vapor from a plant.
A leaf is a plant's principal organ of photosynthesis, the process by which sunlight is used to form foods from carbon dioxide and water. Leaves also help in the process of transpiration, or the loss of water vapor from a plant.
Leaves in autumn
Leaves are green in summer because they contain the pigment chlorophyll, which absorbs all the wavelengths of sunlight except for green (sunlight or white light comprises all the colors of the visible spectrum: red, orange, yellow, green, blue, indigo, and violet). In addition to chlorophyll, leaves contain carotenoid pigments, which appear orange-yellow. In autumn, plants create a barrier of special cells, called the abscission layer, at the base of the petiole. Moisture and nutrients from the plant are cut off and the leaf begins to die. Chlorophyll is very unstable and begins to break down quickly. The carotenoid pigments, which are more stable, remain in the leaf after the chlorophyll has faded, giving the plant a vibrant yellow or gold appearance.
The red autumn color of certain plants comes from a purple-red pigment known as anthocyanin Unlike carotenoids, anthocyanins are not present in a leaf during the summer. They are produced only after a leaf starts to die. During the autumn cycle of warm days and cool nights, sugars remaining in the leaf undergo a chemical reaction, producing anthocyanins.
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