Photochemistry Essay Example

  • Category:
    Chemistry
  • Document type:
    Coursework
  • Level:
    Undergraduate
  • Page:
    1
  • Words:
    585

Photochemistry of photosynthesis

When visible or ultraviolet light is absorbed by a molecule, it introduces energy that is enough to break or reorganizes covalent bonds. There are two important principles of photochemistry. The first law states that a compound must absorb light first before any photochemical reaction take place. The second law states that for every photon of light that is absorbed by a chemical system, only one molecule is activated for the chemical reaction.

Photosynthesis is a process in which plants convert light energy into chemical energy that is used to fuel plant activities. The energy is then stored in carbohydrates molecules like sugars. There are 3 processes involved in photosynthesis. The first process is production of oxygen through the removal of hydrogen atoms from H20, the second process is the transfer of hydrogen from the stage 1 intermediate to stage 3 intermediate, and lastly is the conversion of carbon dioxide into carbohydrates. There are photosynthesis reactions that depend on light and those that do not depend on light. The light is absorbed by use of pigment chlorophyll which is green in color. In the process of photosynthesis, CO2 is converted into sugar through a process called carbon fixation, this is an endothermic redox reaction, which means energy is required to drive this process and electrons are required to convert CO2 into carbohydrates. The general equation of photosynthesis is 2n CO2 + 2n DH2 + photons → nO)22(CH + 2n DO. CO2 + electron donor + light energy → carbohydrate + oxidized electron donor.

There are two stages in which photosynthesis takes place, light depend and light reaction stage. The process takes place in chloroplast. When light strike the chlorophyll pigment, it absorbs one photon of light and loses one electron. The electron lost is passed to modified chlorophyll called pheophytin, pheophytin the passes it to quinone molecule, this will begin the flow of electrons that will lead to the reduction of NADP to NADPH. The lost molecule in the chlorophyll will be regained from water through a process known as photolysis. The equation of light reactions in green plants is 2 H2O + 2 NADP+ + 3 ADP + 3 Pi + light → 2 NADPH + 2 H+ + 3 ATP + O2.

The reactions that depend on light take place in thylakoid membranes of chloroplasts; energy from light is used to synthesis ATP and NADPH. The reactions that depend on light are in two forms, cyclic and non-cyclic reaction. In these reactions, light photons are captured by light harvesting antenna complexes of photo system II of chlorophyll. The two differs in that non-cyclic only generates ATP and reduced NADP is not created. In the reactions that do not depend on light, enzymes called RuBisCO captures carbon dioxide from atmosphere and through a process that require NADPH known as Calvin-Benson Cycle, 3 carbon sugars are released which will combine later to form sucrose and starch. The equation for this reaction therefore is 3 CO2 + 9 ATP + 6 NADPH + 6 H+ → C3H6O3-phosphate + 9 ADP + 8 Pi + 6 NADP+ + 3 H2O.

References

Symposium on Chlorophyll Organization and Energy Transfer in Photosynthesis, Wolstenholme,

G. E. W., FitzSimons, D. W., & Ciba Foundation. (1979). Chlorophyll organization and energy transfer in photosynthesis. Amsterdam: Excerpta Medica.

McCally, J., Rogers, C. W., Youngdahl, K., Stone House Productions., New York Botanical

Garden., & Schlessinger Media. (2006). Photosynthesis. Wynnewood, PA: Schlessinger Media.

Bowen, E. J. (1946). The chemical aspects of light. Oxford: Clarendon Press.