How Long Does Photosynthesis Take?

The strength of light available to the plant affects the photosynthesis process. The light-dependent stage of photosynthesis can take place only when there is enough light available for the plant to absorb. When there is not enough light, pigments such as chlorophyll cannot absorb enough light energy to create adenosine triphosphate, also known as ATP. ATP is a chemical used by the plant to store energy, and is a necessary component in the second phase of photosynthesis, which is called the light-independent phase. For this reason, while photosynthesis can begin only during daylight, once the ATP has been created, the process can complete at any time that the appropriate amount of water and carbon dioxide is available.

Photosynthesis requires a certain amount of carbon dioxide in order to be successful. The amount of carbon dioxide available in the atmosphere lessens at higher elevations, which slows the photosynthesis process. At extremely high elevations, a lack of carbon dioxide can prevent the process entirely. In addition to carbon dioxide, the plant also requires water for the chemical reaction that creates sugar. Each molecule of sugar produced by the plant requires six molecules of water. The water molecules provide hydrogen, leaving the remaining oxygen as a waste product. If the amount of water available is not enough to complete the process, photosynthesis stops until more water is available.

Although the rate of photosynthesis differs between plant species and environmental factors, it is possible to determine the exact rate of photosynthesis of a particular plant. In an experiment conducted at the University of Colorado, the rate of photosynthesis accomplished by deciduous tree leaves was tested. In this experiment, it was determined that the leaves tested processed 44.14 ppm (parts per million) of carbon dioxide gas in each minute of photosynthesis for every gram of leaf surface.