Effect of Light on Photosynthesis

Photosynthesis is the process by which sunlight is captured by chloroplasts within plant cells and turned into energy. This energy is used to help the plant grow roots, leaves, flowers and fruit. Photosynthesis is an extremely important process because plant tissues serve as the bottom of every food chain on earth. The process of photosynthesis is dictated by a number of factors, one of which is light.

Light Intensity

The intensity of light can affect the process of photosynthesis. Brighter light causes more light to hit the surface of a plant or algae, which increases the rate of photosynthesis. Thus, there tend to be higher rates of photosynthesis in climates with a lot of sun compared to areas that are predominantly cloudy. That is why algae and other organisms that photosynthesize must live in the upper layers of the water, where sufficient light penetrates.

Light Wavelengths

The rate of photosynthesis is also affected by the wavelength of the light that is present. Visible light contains wavelengths that vary in length from about 400nm (nanometers) to 700nm. Pigments in plant cells vary in the wavelengths of light they absorb and reflect. Chlorophyll, for instance, is one of the main pigments necessary for photosynthesis. It reflects green light (which is why leaves appear green to us) and absorbs wavelengths of light that are red and blue. Plants grown in red light, therefore, grow much better than plants grown in green light.

Exposure Duration

The length of time a plant is exposed to light can have an impact on photosynthesis. Although photosynthesis can occur in the dark, reactions that occur in the daylight are much more efficient. Thus, plants in areas of the world having long photoperiods undergo high rates of photosynthesis relatively speaking. Plants in Alaska, for instance, can grow very large in the summertime when the amount of sunlight during a given day is high. Plants in the tropics, which receive a lot of light year round (e.g., the rain forest), grow very large as well.

Dark Reactions

Photosynthesis can occur in the dark, through a series of what are known as "dark reactions." However, dark reactions in photosynthesis are less efficient and will result in slower growth of the plant.

Other Factors

Regardless of the quality of light present, at some point the rate of photosynthesis becomes less dependent on the intensity of light when it is limited by some other factor (e.g., the amount of nutrients available for the plant).

[joebowden]

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