Introduction to Photosynthesis
Photosynthesis is the process by which plants convert solar energy into the life-sustaining chemical energy called ATP. Photosynthesis occurs in plants and some species of algae that are considered protozoans. Photosynthesis requires water and carbon dioxide to occur, and produces sugar and oxygen as a result. Oxygen is necessary for sustaining life on Earth and sugar is used for energy.
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Beginnings
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Photosynthesis begins in the ground. Plants' roots take in water and transport it up the stem to the leaves via special cells, called xylem cells. Photosynthesis occurs in the leaves. There is only one way for materials to enter and exit the leaves--through holes, called stomata, which are surrounded by guard cells.
Pigment & Structure
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Chlorophyll, the green pigment in plants, is the instigator of the photosynthetic process. The cellular membranes of plants contains proteins, called chloroplasts, without which light from the sun would be released as heat or fluorescence instead of triggering photosynthesis. Inside the chloroplasts are thylakoids, flat thin discs that stack together to form grana, the structures in which the light reaction chemicals reside.
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Chemical Formula
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The chemical formula for photosynthesis is six molecules of water obtained from the roots, added to six molecules of carbon dioxide obtained from the air. The molecular combination produces one molecule of sugar that is stored in the plant and six molecules of oxygen that are released into the air. The plants convert the sugar to ATP to use as energy and the process begins again.
Light Dependent Process
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Photosynthesis is a two-stage process. The first stage is light dependent. The light dependent stage occurs in the grana and requires direct sunlight. The light strikes the plant, putting the chlorophyll into a high-energy state. The resulting energy chemicals form covalent bonds of carbohydrates, and water is released. Carbon dioxide is taken from the atmosphere, a process called carbon fixation, and modified by the addition of a hydrogen molecule.
Light Independent Process
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As the name implies, the light independent process can occur in the dark and takes place in the stroma, or spaces between the grana layers. Carbon dioxide diffuses into cells; six carbon dioxide molecules begin a process called the Calvin Cycle, a series of enzymatic reactions that results in the formation of one glucose (sugar) molecule.
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