Chlorophyll, the green pigment (coloring matter) found in all food-making organisms. Together with light, water, and air, chlorophyll makes it possible for plants, through the process of photosynthesis, to make food.

Chlorophyll is formed only when there is light. Plants kept in darkness for a time become white and waxy. Chlorophyll, which is formed in leaves, stems, and other parts of plants, is located in cell bodies called chloroplasts. In a leaf, the chloroplasts accumulate usually in the upper cells, giving the surface a greener color than the underparts. The reds and other brilliant hues of autumn foliage result when the amount of chlorophyll decreases and other pigments are revealed.

Chlorophyll is a very complex substance containing carbon, hydrogen, magnesium, nitrogen, and oxygen. It is insoluble in water, but readily soluble in alcohol, chloroform, or ether. There are about 10 different kinds of chlorophyll—designated as chlorophyll a, b, c, and so on—differing somewhat in their chemical structure.

Chlorophyll has many commercial uses. For such uses it is extracted from plant material and purified. It is used, for example, to color soaps, oils, cosmetics, medicines, liquors, and candies. Chlorophyll is also used as a sensitizer for color film and as a source of phytol, an alcohol used in the synthesis of vitamins E and K.