Photosynthesis article provided by the Britannica Encyclopedia
The process by which green plants and certain other organisms transform light energy into chemical energy. During photosynthesis in green plants, light energy is captured and used to convert water, carbon dioxide, and minerals into oxygen and energy-rich organic compounds.
It would be impossible to overestimate the importance of photosynthesis in the maintenance of life on Earth. If photosynthesis ceased, there would soon be little food or other organic matter on Earth. Most organisms would disappear, and in time the Earth's atmosphere would become nearly devoid of gaseous oxygen. The only organisms able to exist under such conditions would be the chemosynthetic bacteria, which can utilize the chemical energy of certain inorganic compounds and thus are not dependent on the conversion of light energy.
Photosynthesis also is responsible for the "fossil fuels" (i.e., coal, oil, and gas) that power industrial society. In past ages, green plants and small organisms that fed on plants increased faster than they were consumed, and their remains were deposited in the Earth's crust by sedimentation and other geological processes. There, protected from oxidation, these organic remains were slowly converted to fossil fuels. These fuels not only provide much of the energy used in factories, homes, and transportation, but they also serve as the raw material for plastics and other synthetic products. Unfortunately, modern civilization is using up in a few centuries the excess of photosynthetic production accumulated over millions of years.
Requirements for food, materials, and energy in a world where human population is rapidly growing have created a need to increase both the amount of photosynthesis and the efficiency of converting photosynthetic output into products useful to people. One response to these needs--the so-called "Green Revolution"--has achieved enormous improvements in agricultural yield through the use of chemical fertilizers, pest and plant disease control, plant breeding, and mechanized tilling, harvesting, and crop processing. This effort has limited severe famines to a few areas of the world despite rapid population growth, but it has not eliminated widespread malnutrition.
A second agricultural revolution, based on plant genetic engineering, may lead to increases in plant productivity and thereby partially alleviate malnutrition. Since the 1970s, molecular biologists have possessed the means to manipulate a plant's genetic material (DNA) to achieve improvements in disease and drought resistance, product yield and quality, frost hardiness, and other desirable properties. In the future, such genetic engineering may result in improvements in the process of photosynthesis.
Britannica has more info and pictures .