Photosynthesis refers to the process by which plants and other organisms as photosynthetic bacterias convert light from the sun into chemical energy that they use for survival. The energy released is vital for the functioning of the plants and the support of life on earth. For photosynthesis to take place, there are four basic factors that must be fulfilled. These include carbon dioxide, water, sunlight, and chlorophyll. Therefore, the process of photosynthesis helps remove carbon dioxide from the atmosphere. One of the byproducts of the process of photosynthesis is oxygen, a vital gas for the survival of animals on earth.
All organisms that are capable of photosynthesizing are called photoautotrophs. In algae, cyanobacteria, and plants the process of photosynthesis mainly produces oxygen and is thus referred to as oxygen photosynthesis. However, there are some bacterial that use carbon dioxide during photosynthesis but do not release oxygen. Such photosynthesis is called anoxygenic photosynthesis.
In oxygen photosynthesis, the photoautotrophs reduce CO2 to a carbohydrate and removes an electron from water (H2 O) leading to production of oxygen (O2). In this case, water is oxidized in the multisubunit protein in the photosynthetic membrane by the photosystem II reaction. Research has shown that the function and structure of the photosystem II in certain bacterias, algae, and plants is similar. The common equation is therefore as follows;
In general, the photosynthesis equation is 2n CO2 + photons + 2n DH2 → 2(CH2O)n + 2n DO i.e.
Carbon dioxide + light energy + electron donor carbohydrate + oxidized electron donor
In the oxygenic photosynthesis would thus be
Water + carbon dioxide + light energy Oxygen +carbohydrate + water i.e.
2n CO2 + photons + 4n H2O → 2(CH2O)n + 2n H2O+ 2n O2
It involves the use of the carbon dioxide during the process of the photosynthesis. However, the photoautotrophic bacteria are incapable of extracting an electron from water and hence cannot lead to production of oxygen as byproduct.
Basically, there are two stages of photosynthesis; light-dependent stage and light-independent stage.
Light dependent stage of photosynthesis
This occurs during the light reactions. During this stage, a molecule of pigment chlorophyll (The green matter) absorbs a proton and at the same time losses an electron. The electron lost passes through pheophytin, and then to a Quinone molecule leading to a flow of electrons down the electro transport chain reducing the NADP to NADPH. The result is a creation of a proton gradient that activates the formation of ATP. The chlorophyll molecule regains the electron lost from a water molecule. The process is referred to as photolysis. Photolysis leads to the formation of a dioxygen (O2). This process is summarized in the equation below
2 H2O + 2 NADP+ + 3 ADP + 3 Pi + light → 2 NADPH + 2 H+ + 3 ATP + O2
In summary, the light-dependent stage in plants takes place in the thylakoid membranes of the chloroplasts. It uses light to synthesis the ATP and the NADPH.
Light-independent reactions (dark stage)
During this stage, the enzyme Rubisco capture carbon dioxide from the atmosphere using the NADPH produced in the light stage. The process releases three-carbon sugars that combine to form starch and sucrose. The process is summarized below;
3 CO2 + 9 ATP + 6 NADPH + 6 H+ → C3H6O3-phosphate + 9 ADP + 8 Pi + 6 NADP+ + 3 H2O
The process involves simply a fixation of carbon dioxide that produces carbohydrates.
Significance of photosynthesis
The process supports life in two main ways. First, it produces of food, and secondly production of oxygen, both of which a vital for survival. It also helps in reducing global warming and climate change by using the excess carbon dioxide from the atmosphere.
John Whitmarsh and Govindjee (n.d) The photosynthetic process. Retrieved from http://www.life.illinois.edu/govindjee/paper/gov.html on 7th May, 2014.