BIO 204 Week2 Process of Photosynthesis

Photosynthesis Process





Photosynthesis Process

The process of photosynthesis needs water, carbon dioxide as well as sunlight to produce oxygen and glucose. The plant acquires the carbon dioxide through their leaves. In essence, the leaves have minute holes that are known as stomata that are the entrance through which carbon dioxide passes through (Cakmak&Yazici, 2010). Besides, the plants also have the chlorophyll molecules that help in absorbing energy that is in form of sun light. The roots help in absorbing water from the soil that serves an important part in the photosynthesis process. Oxygen is critical in the breathing process since people have to inhale it. It then helps in the respiration process, which are one of the processes that keep man alive. Glucose serves as a nutrient in most plants. It helps in giving energy to man; hence, he or she can engage in productive activities in the society. The following equation demonstrates the photosynthesis process.

6CO2 + 6H2O ——> C6H12O6 + 6O2

Absorption spectra occur when the pigments are absorbing light into the molecules. The leaf fails to absorb the green light appropriately; hence, when it absorbs the white light it shines and reflects green rays on the leaves that end up giving it the green color instead. Most plant pigment cannot exceed wavelength of 700 nm (Chen& Blankenship, 2011). Often, violet and blue tend to have the shortest wavelengths while red has less energy and longest wavelengths. The pigments end up reflecting the wavelength that they cannot absorb; hence, they retain the color of that wavelength. Hence, the reason some are red in color since they reflect the red wavelength they can absorb because they are the longest.

ATP and glucose are the two molecules that serve the purpose of carrying energy. Glucose comprises of a molecule (C6H12O6) that carries energy used by the cells. It is carried in the blood and flows through in the capillaries in huge numbers. ATP stores energy in the three phosphate molecules it has. It releases the energy when the phosphates break the bond between the phosphate groups instead. After releasing the energy, it turns to ADP but it can regain the energy from respiration to bind the phosphate groups (Melis, 2013).

The light reaction depends on the presence of light to manufacture food in the end. The process takes place in the chloroplast’s thylakoids that have a large surface area critical to the absorption of light. The light reaction stage helps in manufacturing ATP and NADP that are later used in the Calvin cycle. The process entails two photosystems that have chlorophyll and other important molecules. The first that is photosystem II often absorbs light that does not exceed 680 nm (P680) wavelengths (Hall et al, 2013). Photosystem I absorbs a wavelength of about 700 nm (P700). The chlorophyll molecules in the chloroplasts help in absorbing more light for the plant. When one molecule of P680 loses electrons, it goes to a higher energy level and becomes a positively charged molecule. Despite the molecule losing electrons, photolysis provides electrons for stabilizing the molecule. In essence, photolysis entails the process where light splits water. The oxygen from photosystem serves as an enzyme that helps in the oxidation of the water. Based on the reaction 2H2O 4 H+ + 4e- + O2, the Hydrogen ions then diffuse into the thylakoid. When the Hydrogen ions enter the chloroplast, it turns the ADP + Pi to ATP {Appendix 1}. In summary, the electrons leaving the PSII are all positively charged. The electrons then become less stable and weak thereby diffusing to chlorophyll in the photosystem I (PSI). In P700, they are also raised to higher energy level as well. The scenario makes them electron acceptors in the end. The electrons then pass to the NADP. Both ATP and NADP serve as raw materials for the Calvin Cycle stage.

The Calvin Cycle does not solely depend on light to produce food for the plant. The raw materials used in the stages are products of the light stages; hence, there is no need for light again. It entails three stages that include fixation, reduction, as well as regeneration. In general, the Calvin Cycle involves reactions that help in converting compounds that include carbon dioxide into glucose.

The fixation process depends on a number of components to “fix” CO2 from the inorganic to organic state. First, it needs the ribulose bisphosphate carboxylase (RuBisCO), which as an enzyme as well as ribulose bisphosphate (RuBP) that provides three molecules for the process. In fact, RuBP has five atoms from carbon and two phosphates (Melis, 2013). RuBisCO serves the purpose of catalyzing the reaction between RuBP and CO2. The reaction of one CO2 molecule and one RuBP molecule amounts to two molecules of 3-phosphoglyceric acid (3-PGA). The second stage that is the reduction stage entails the 3-PGA gaining more electrons. The products of the light stage which are ATP and NADPH serves the purpose of converting the 3-PGA to glyceraldehyde 3-phosphate (G3P). ATP turns to ADP while NADPH converts to NADP since they have lost energy. However, they gain more electrons from the nearby operations that use light instead. Lastly, the regeneration stage uses one G3P molecule in creating other crucial compounds that the plant needs. Given that G3P had three molecules, the process occurs in three cycles as well. Besides, each cycle has two G3Ps thereby amounting to six G3Ps. The process uses only one molecule while the five remaining regenerate RuBP.

6CO2 + 6H2O ——> C6H12O6 + 6O2

In the Calvin Cycle, CO2 is the only product used since it serves as a raw material in the fixation stage. First, the name fixation arises from the fact that CO2 is fixed to the organic form from the inorganic molecules. In the fixation stage, the reaction between RuBP and CO2 needs the presence of RuBisCO that serves as a catalyzer. The reaction leads to the 3-phosphoglyceric acid (3-PGA) in the end (Hall et al, 2013). In the light reaction, water is influential based on the products from photolysis. The process entails sunlight splitting water to Oxygen, electrons and Hydrogen ions. The hydrogen ions in question turn ADP + Pi to ATP. The positively charged electrons, on the other hand, help in reducing NADP. The two are then passed to Calvin cycle where they serve as raw materials. The oxygen is produced in the Light reaction during photolysis. Based on the process (2H2O 4 H+ + 4e- + O2) sunlight splits water to Hydrogen ions, electrons and Oxygen. In the Calvin Cycle, a reaction between ATP and CO2 creates glucose in the photosynthesis (Hall et al, 2013).


Cakmak, I., &Yazici, A. M. (2010). Magnesium: a forgotten element in crop production. Better Crops, 94(2), 23-25.

Chen, M., & Blankenship, R. E. (2011). Expanding the solar spectrum used by photosynthesis. Trends in plant science, 16(8), 427-431.

Hall, D. O., Scurlock, J. M. O., Bolhar-Nordenkampf, H. R., Leegood, R. C., & Long, S. P. (Eds.). (2013). Photosynthesis and production in a changing environment: a field and laboratory manual. Springer Science & Business Media.

Melis, A. (2013). Carbon partitioning in photosynthesis. Current opinion in chemical biology, 17(3), 453-456.

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