plant growth & development
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Photosynthesis
One of the major differences between plants and animals is plants' ability to manufacture their own food. This process is called photosynthesis,which literally means "to put together with light." To produce food, a plant requires energy from the sun, carbon dioxide from the air, and water from the soil. During photosynthesis, it splits carbon dioxide into carbon and oxygen, adds water, and forms carbohydrates (starches and sugars). Oxygen is a by-product.The formula for photosynthesis can be written as follows:
or
6 CO2 + 6 H20 + Energy => C6H1206 + 6 02
After producing carbohydrates, a plant either uses them as energy, stores them, or builds them into complex energy compounds such as oils and proteins. All of these food products are called photosynthates. The plant uses them when light is limited, or transports them to its roots or developing fruits.
Photosynthesis occurs only in the mesophyll layers of plant leaves and, in some instances, in mesophyll cells in the stem. Mesophyll cells are sandwiched between the leaf's upper and lower epidermis and contain numerous chloroplasts ( Figure 12), where photosynthesis takes place. Chloroplasts are incredibly small. One square millimeter, about the size of a period on a page, would contain 400,000 chloroplasts.
Chlorophyll, the pigment that makes leaves green, is found in the chloroplasts. It is responsible for trapping light energy from the sun. Often chloroplasts are arranged perpendicular to incoming sun rays so they can absorb maximum sunlight. If any of the ingredients for photosynthesis--light, water, and carbon dioxide--is lacking, photosynthesis stops. If any factor is absent for a long period of time, a plant will die. Each of these factors is described below.
