Photosynthesis is the process used by plants, algae and certain bacteria to harness energy from sunlight into chemical energy. It is one example of how people and plants are dependent on each other in sustaining life. Photosynthesis happens when water is absorbed by the roots of green plants and is carried to the leaves by the xylem, and carbon dioxide is obtained from air that enters the leaves through the stomata and diffuses to the cells containing chlorophyll. The green pigment chlorophyll is uniquely capable of converting the active energy of light into a latent form that can be stored (in food) and used when needed. Photosynthesis provides us with most of the oxygen we need in order to breathe. We, in turn, exhale the carbon dioxide needed by plants. Plants are also crucial to human life because we rely on them as a source of food for ourselves and for the animals that we eat. There are two types of photosynthetic processes: oxygenic photosynthesis and anoxygenic photosynthesis. Oxygenic photosynthesis is the most common and is seen in plants, algae and cyanobacteria. On the other hand, anoxygenic photosynthesis uses electron donors other than water. The process typically occurs in bacteria such as purple bacteria and green sulfur bacteria. Plants make simple sugar by photosynthesis. It all happens in a fraction of a second. Water gets split into hydrogen and oxygen. The hydrogen is combined chemically with carbon dioxide to produce simple sugar. This dissolves easily in water and hence is transported to all parts of the plant. Oxygen is given off as a by-product. Thus, plants take in CO2 and gives out oxygen during photosynthesis reaction. Sun shines each day and does not charge us any money for the light it gives us. The light falling on Earth is very clean and will be there for a very long time as long as the Sun lasts. In addition to the current applications, Photosynthesis-based technology could also include using the concept of efficient “energy capture” to our artificial systems just as plants have been doing: thousands of chlorophyll a molecules (antenna) serving one center where the process occurs efficiently; the use of compounds, produced by plants, in triggering reactions that kill cancer cells; and the use of photosynthetic organisms in cleaning of aqueous surface environments (lakes, etc). An excellent example is in the use of cyanobacteria that literally eat up the nitrates from ground water and clear it for us. The opportunities that photosynthesis-based technology provides us are enormous. This process is extremely important for life on earth as it provides the oxygen that all other life depends on.