How Photosynthesis Works
Photosynthesis is one of the most important chemical processes in life
A direct connection exists between quantum physics, light and life. It is called photosynthesis and it is essential to almost all life on Earth. There are organisms that exist outside of the photosynthesis loop, but they are comparatively few and rare in comparison to the biomass dependant on photosynthesis.
Photosynthesis is a chemical process that is triggered by a fundamental law of physics; the photoelectric effect. As everything is made up of atoms and sub-atomic particles, it is little wonder that chloroplasts and chlorophyll in plants utilize an important factor in quantum physics. What is a wonder is that evolution occurred to exploit the photoelectric effect as a source of energy. The fact that most leaves reflect the green wavelength of light should tell us something. The same leaves absorb the blue and red wavelengths of light which just happen to be the types of wavelengths that will trigger hydrogen to lose an electron. These wavelengths are 656.28 nanometers for hydrogen red alpha and 486.13 nanometers for hydrogen blue beta. Hydrogen atoms will absorb and release only light in the blue, ultraviolet and the red end of the electromagnetic spectrum. Once the photon of the correct wavelength contacts the electron shell of the water molecule, it ionizes the molecule and breaks it down in a process called reduction, releasing oxygen molecule and the free radical hydrogen proton is then captured by a carbon dioxide molecule in the process of being converted to sugar. There are four discrete stages in the process of photosynthesis. The first one has been described and this is the stage where high energy molecules are assembled. This is called the Light Reaction stage of photosynthesis.
The process of absorbing certain wavelengths also tells us why photosynthesis is only about six percent efficient. All other wavelengths are either reflected or pass through. This is consistent with the photoelectric effect. Oxygen and carbon, which also play a part in photosynthesis, have many more wavelengths that can be emitted and absorbed. The process of photosynthesis uses only one percent of the electromagnetic spectrum and two percent of the visible electromagnetic spectrum.
The next stage is light independent and it is called the Calvin-Bensen cycle or the Dark Reactions. In this stage, the high energy molecules help to chemically reduce carbon dioxide. This is necessary in order to create the precursors to carbohydrates. During the Light Reaction phase, the pigment chlorophyll absorbs a photon and loses an electron. This electron is passed to a modified form of chlorophyll called pheophytin, which then passes the electron to a quinone molecule, which allows the start of a flow of electrons down an electron transport chain that leads to the ultimate reduction of NADP to NADPH (Nicotinamide adenine dinucleotide phosphate). A proton gradient is created across the chloroplast membrane. The dissipation of the proton is used by ATP synthesis to make ATP (adenosine triphosphate). The chlorophyll molecule regains an electron by taking it from water and releasing an oxygen molecule (O2). The common equation for the chemical reaction of photosynthesis is;
6 CO2 + 12 H2O + photons → C6H12O6 + 6 O2 + 6 H2O
which can also be written as;
carbon dioxide + water + light energy → glucose + oxygen + water
The light independent part requires carbon dioxide, which is captured from the atmosphere. The enzyme, Ribulose-1,5-bisphosphate carboxylase/oxygenase catalyzes the first cycle of carbon fixation. This step is crucial in the manufacture of sucrose, an energy molecule necessary for the fueling of biological processes. This is part of the Calvin Bensen Cycle and three types of molecules are made to make carbon based sugars and starches. This particular protein is considered the most important one on Earth and it is found in all plants and animals. The manufacture of carbohydrates is necessary in the production of cellulose that figures so importantly in cell walls.
The final phase is carbon fixation and the export of stable chemical products to the rest of the cell or for transport to other cells in a complex organism like a tree. These chemical products are used for the growth of new cells, the repair of existing ones or for the eventual production of seeds to propegate the next generation. These final reactions take a millisecond to a second to complete..
Most plants are photoautotrophs, which mean that they can synthesize food directly from inorganic compounds using the parts of the electromagnetic spectrum to drive the process. Water is used as the reducing agent in order to provide the energy to drive the whole process. Thus most light driven plants literally use appropriate photons to drive the whole process of life. These plants are everything from algae, cyanobacteria, annual plants and perannuals such as trees and shrubs.
Chlorophyll is contained in organelles which the plant moves to the light source of sunward side of the leaf. The cells in the interior tissues of a leaf, called the mesophyll, can contain between 450,000 and 800,000 chloroplasts for every square millimeter of leaf. This maximizes the potential for the capture of photons and for the creation of the surplus of energy required for the creation of sugars, starches and the eventual creation of protiens. Photosynthesis is affected by the quantity of light, the temperature and the availability of trace elements that assist in plant growth and the production of chlorophyll. There are many complex processes involved in turning light into useful protiens and starches, but the foundation is light of specific wavelengths that causes electron emission.
Stern, Kingsley R., Shelley Jansky, James E Bidlack, 2003. Introductory Plant Biology. McGraw Hill. ISBN 0-07-290941-2
Video depiction of photosynthesis
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