BIOLOGY Volume 1 - A Guide to General Biology - 2004

7. AUTOTROPHIC NUTRITION

7.3. The Importance of Photosynthesis

Almost all life on Earth depends, directly or indirectly (as in the case of animals), upon Photosynthesis. The process provides sources of carbon and energy that are accessible to living organisms; in addition, it releases oxygen, which is vital for aerobic forms of life. Humanity is also dependent on photosynthesis, as we rely on fossil fuels that have accumulated over millions of years.

Of the total solar radiation directed toward the Earth, about half reaches its surface, while the rest is absorbed, reflected, or scattered in the atmosphere. Of the radiation reaching the Earth, only about 50% is capable of driving photosynthesis and, by rough estimates, roughly 0.2% is utilized by plants for synthesis (about 0.5% of the energy that actually reaches a leaf). This small fraction of available energy essentially sustains all life on Earth. About 40% of all photosynthesis is carried out by microscopic Algae—phytoplankton—living in the oceans.