Sunlight is one of the two most important climatic factors for ecosystems, according to experts from the University of Illinois Extension. Exposure to sunlight also helps humans synthesize vitamin D, which helps the muscular, skeletal and nervous systems work properly.
Some species produce their own food by converting energy from sunlight into organic compounds, according to About.com. The amount of light a plant receives has a direct effect on the growth of the plant, while the duration of exposure to sunlight affects the behavior of insects and animals in an ecosystem. Sunlight also plays an important role in regulating the temperature of an ecosystem.
Humans synthesize vitamin D when they are exposed to the short ultraviolet rays in sunlight. The number of UVB photons absorbed by the skin dictates how much vitamin D is synthesized. Clothing, the use of sunscreen and the amount of melanin in the skin all have an effect on the number of photons absorbed. The body initially produces a form of vitamin D called vitamin D-3, but some of it is converted into 25-hydroxyvitamin D by the liver, kidneys and other tissues. The human body uses vitamin D to transmit nerve impulses from the muscles, maintain normal phosphorus and calcium levels, and build strong bones.