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Photosynthesis, is a food-making process that occurs in green plants. Photosynthesis is the chief function of leaves. The word photosynthesis means putting together with light. Green plants use energy from light to combine carbon dioxide and water to make food. All our food comes from this important energy-converting activity of green plants. Light energy is converted to chemical energy and is stored in the food that is made by green plants. Animals eat the plants, and we eat animal products as well as plants. The light used in photosynthesis is absorbed by a green pigment called chlorophyll. Each food-making cell in a plant leaf contains chlorophyll in small bodies called chloroplasts. In chloroplasts, light energy causes water drawn from the soil to split into molecules of hydrogen and oxygen. In a series of complicated steps, the hydrogen combines with carbon dioxide from the air, forming a simple sugar. Oxygen from the water molecules is given off in the process. From sugar--together with nitrogen, sulfur, and phosphorus from the soil--green plants can make starch, fat, protein, vitamins, and other complex compounds essential for life. Photosynthesis provides the chemical energy needed to produce these compounds. Certain bacteria and algae can also capture light energy and use it to make food. For example, photosynthetic bacteria contain chlorophyll in tiny bodies called chromatophores. In chromatophores, compounds other than water are combined with carbon dioxide to form sugar. No oxygen is released.Green plants convert carbon dioxide and water into food and oxygen. Plants and animals, in turn, "burn" the food by combining it with oxygen to release energy for growth and other activities of life. This process, which is called respiration, is the reverse of photosynthesis. Oxygen is used up and carbon dioxide and water are given off. Plants then use the carbon dioxide and water to produce more food and oxygen. The cycle of photosynthesis and respiration maintains the earth's natural balance of carbon dioxide and oxygen. Chlorophyll is the green pigment in plants that absorbs light energy for use in photosynthesis. Chlorophyll also is found in simple organisms called algae and in some bacteria. Most plant cells do not produce chlorophyll unless the plant is exposed to light. This is why plants kept away from light are white or yellow rather than green. Chlorophyll is located in disk-shaped membranes called thylakoids within cells. In most plants, thylakoids are contained in tiny cell bodies called chloroplasts. The chloroplasts in the leaves of plants carry out all the essential processes of photosynthesis. Light energy absorbed by chlorophyll is channeled to specialized reaction centers in the thylakoids. The reaction centers, along with electron-carrier molecules, convert the light energy to chemical energy. Oxygen is released in the process. Chemical energy is needed for taking carbon dioxide from the air, eventually leading to the production of sugars and such other food substances as starch, fat, protein, and vitamins. There are several forms of chlorophyll. The most common forms in plants are chlorophyll a and chlorophyll b. They absorb most of the long wavelengths (red rays) and the short wavelengths (blue-violet rays) of visible light. They absorb the middle wavelengths (green rays) least effectively. Some bacteria, like plants, make their own food by photosynthesis. These bacteria have special chlorophylls that can absorb longer wavelengths called infrared rays, which lie beyond the visible light spectrum. When dried, chlorophyll looks like blue or green-black powder.