Photosynthesis Earth's atmosphere, and supplies all of the organic compounds and most of the energy necessary for life on Earth. Although photosynthesis is performed differently by different species, the process always begins when energy from light is absorbed by proteins called reaction centres that contain green chlorophyll pigments. In plants, these proteins are held inside organelles called chloroplasts, which are most abundant in leaf cells, while in bacteria they are embedded in the plasma membrane. In these light-dependent reactions, some energy is used to strip electrons from suitable substances, such as water, producing oxygen gas. The hydrogen freed by the splitting
Photosynthesis water, and the availability of suitable temperatures for carrying out photosynthesis. The process of photosynthesis provides the main input of free energy into the biosphere, and is one of four main ways in which radiation is important for plant life. The radiation climate within plant communities is extremely variable, with both time and space. In the early 20th century, Frederick Blackman and Gabrielle Matthaei investigated the effects of light intensity (irradiance) and temperature on the rate of carbon assimilation. These two experiments illustrate several important points: First, it is known that, in general, photochemical reactions are not affected by temperature.