Through the process of photosynthesis, sun light is absorbed by plants and converted into chemical energy. Using that chemical energy, the plants are then able to absorb carbon dioxide from the atmosphere and turn it into food for themselves. A beneficial byproduct of that food production is oxygen, which humans need in order to breathe. Photosynthesis will occur in plants, algaes, and different species of bacteria, and organisms that can perform photosynthesis are referred to as photoautotrophs, meaning they can create their own food. Photosynthesis is vital to life on Earth as it helps maintain normal levels of oxygen in the air which is necessary for survival of most species.
Sun and Light
Light from the sun is actually energy, and is advantageous to the Earth in several ways. One of the most important ways is through photosynthesis. Plants absorb the red and blue wavelengths of light energy, and reflect the green wavelength. This is why plants appear to be green; that is the color not being absorbed by the plants.
In leafy plants, the process of photosynthesis occurs largely in the leaves. Because of this, all the necessary ingredients need to be present in the leaves for the reaction to take place. Carbon dioxide is absorbed into the leaves from the air, water is routed from the roots to the leaves, and sunlight is absorbed into the leaves through chlorophyll. Chlorophyll is a green pigment inside plant cells called chloroplasts - which also have several other structures within them. Chloroplasts are important because they are where photosynthesis takes place.
Photosynthesis and all associated reactions take place at the molecular level. These microscopic reactions involve several molecules aside from chlorophyll. Some of the other molecules are water (H2O), carbon dioxide (CO2), oxygen (O2), and glucose (C6H12O6). All of the components are necessary and the absence of any one of them causes the entire process to fail. For example, if there is no water available to the plant roots, they will begin to turn brown and die, effectively stopping photosynthesis. Oxygen and glucose are not used in photosynthesis, but are byproducts of the reaction. Oxygen is released into the air, and glucose is stored inside the plant cells.
Light and Dark Reactions
Photosynthesis is not an immediate process. The entire chain of events will not occur as soon as the sunlight hits the leaves. Some of it will actually occur in darkness when there is no visible sunlight. Photosynthesis is split into two separate parts referred to light dependent and light independent reactions. The light dependent reaction happens when sunlight is captured and used to begin the process, resulting in the creation of a molecule known as ATP. ATP is a free energy containing molecule and is produced through a chain of steps starting when chlorophyll absorbs light energy. The light independent reaction creates glucose through the Calvin cycle, which uses the ATP and carbon dioxide to make sugar. Dark or light independent reactions occur in the stroma of the plant.
What is photosynthesis? - Very detailed information about the process, with good pictures and diagrams.
Where's the beef? - A good site exploring the relationship between respiration and photosynthesis with some pictures and animations.
Evolution – Historical article from a researcher at NASA exploring when photosynthesis first developed on Earth.
The Carbon Cycle – A look at photosynthesis from a different angle. Explore the process through the lens of the movement of carbon.
Melvin Calvin – History of the scientist that unraveled the mystery of photosynthesis, with pictures and information on his early research.
Photosynthesis and Applications – An incredible amount of information about the process, with good pictures and diagrams to increase understanding.
The Photosynthetic Process – A research tool, broken down into a linked table of contents, that covers everything from bacteria to algae.
Animations – Very informative computer animated videos showing the process of photosynthesis. There are two, one for land based plants and one for marine life.
Arizona State University – Homepage for the Center for Bioenergy and Photosynthesis at ASU, which carries out all manner of research into photosynthesis.
Chemistry – Exploring photosynthesis from a chemical standpoint, there are lots of diagrams and formulas here.