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Photosynthesis (/ ˌ f oʊ t ə ˈ s ɪ n θ ə s ɪ s / FOH-tə-SINTH-ə-sis) [1] is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabolism.
Food energy is chemical energy that animals (including humans) derive from their food to sustain their metabolism, including their muscular activity. [ 1 ] Most animals derive most of their energy from aerobic respiration , namely combining the carbohydrates , fats , and proteins with oxygen from air or dissolved in water . [ 2 ]
In the process of photosynthesis, the phosphorylation of ADP to form ATP using the energy of sunlight is called photophosphorylation. Cyclic photophosphorylation occurs in both aerobic and anaerobic conditions, driven by the main primary source of energy available to living organisms, which is sunlight.
The ATP generated in this process is made by substrate-level phosphorylation, which does not require oxygen. Fermentation is less efficient at using the energy from glucose: only 2 ATP are produced per glucose, compared to the 38 ATP per glucose nominally produced by aerobic respiration. Glycolytic ATP, however, is produced more quickly.
Typically, the complete breakdown of one molecule of glucose by aerobic respiration (i.e. involving glycolysis, the citric-acid cycle and oxidative phosphorylation, the last providing the most energy) is usually about 30–32 molecules of ATP. [16] Oxidation of one gram of carbohydrate yields approximately 4 kcal of energy. [3]
Bioenergetic systems are metabolic processes that relate to the flow of energy in living organisms. Those processes convert energy into adenosine triphosphate (ATP), which is the form suitable for muscular activity. There are two main forms of synthesis of ATP: aerobic, which uses oxygen from the bloodstream, and anaerobic, which does not.
Photoautotrophs are organisms that can utilize light energy from sunlight and elements (such as carbon) from inorganic compounds to produce organic materials needed to sustain their own metabolism (i.e. autotrophy). Such biological activities are known as photosynthesis, and examples of such organisms include plants, algae and cyanobacteria.
The following is a breakdown of the energetics of the photosynthesis process from Photosynthesis by Hall and Rao: [6]. Starting with the solar spectrum falling on a leaf, 47% lost due to photons outside the 400–700 nm active range (chlorophyll uses photons between 400 and 700 nm, extracting the energy of one 700 nm photon from each one)