Photosynthesis is the name for the process that occurs within green plants, algae and some bacteria, by which energy from sunlight is converted into energy for the plant. The energy that is produced for the plant by this process is called glucose. The plant often produces more than it needs, so the extra energy gets stored in its leaves, roots and fruit, which may then be consumed by other organisms, in search of a source of energy.
In every green part of the plant, from leaves to stem, there are tens of thousands of plant cells. Each plant cell has 40 to 50 chloroplasts, which are structures found only in plant cells. The space within the chloroplast is divided into disk-shaped compartments called thylakoids. Within the thylakoid membrane is a chemical called chlorophyll, which absorbs and traps the sun's light for use in the process of photosynthesis. Photosynthesis occurs in two stages, called the light-dependent stage, and the light-independent stage.
In the light dependent stage, chlorophyll traps light from the sun and converts it into two molecules called nicotinamide adenine dinucleotide phosphate (NADPH) and adenosine triphosphate (ATP). Certain wavelengths of light, such as blue and red, are best for exciting the electrons within the chlorophyll and setting this process of trapping the light into motion. Green light is the only light in the spectrum that cannot be absorbed by chlorophyll, so it bounces off the plant. This reflective action results in the green color in plants using chlorophyll to produce energy.
The light independent stage occurs in an ongoing chemical cycle. Molecules used at the beginning of the cycle must be replaced in the end of the cycle, for the cycle to continue. The molecule NADPH created in the light-dependent stage combines with carbon dioxide to create sugar molecules with three carbons, which later combine to form starch and sugar for the plant.