Cellular respiration and photosynthesis are closely related, a relationship that enables life to go on. According to Hopkins et al., (2006) the reactants of one process are the products of another. Looking at the cellular respirations equation, it is the exact opposite of photosynthesis.
Photosynthesis: 6CO2 + 6H2O-C6H12O6+6O2
Cellular Respiration: C6H12O6+6O2-6CO2+6H2O
Photosynthesis is responsible for making glucose. The glucose is later used in cellular respiration in making ATP. The glucose is converted to carbon dioxide that is required during the process of photosynthesis. Water on the other hand is broken down in the process of photosynthesis. At the same time, during cellular respiration, hydrogen is combined with oxygen to form water. The process of photosynthesis needs carbon dioxide later releasing oxygen. On the other hand, Hopkins et al., (2006) state that cellular respiration needs oxygen but releases carbon dioxide. Oxygen release is used by living organisms such as human beings for cellular respiration.
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Breathed oxygen is taken through the blood stream to the various cells of the body. In the body cells, cellular respiration takes place and the process takes place in the existence of oxygen. It thus means that lack of oxygen will result in less production of ATP. The two processes are critical parts of the carbon process/cycle (Hopkins et al., 2006). It is the passageway that enables the recycle of carbon. As cellular respiration produces CO2 in the atmosphere, photosynthesis takes on CO2 from the environment. The give-and-take process of cellular respiration and photosynthesis in the atmosphere assist in stabilizing carbon dioxide and oxygen.
Stages of Photosynthesis
There are two stages of photosynthesis; light reactions and Calvin cycle
In stage I, also known as light reactions water helps in changing light energy to chemical energy and oxygen is released as waste. Energy produced is stored in NADPH and ATP. NADHP and ATP are energy carrying molecules that have the role of driving the processing of new carbohydrate particles. According to Hopkins et al., (2006) the stage occurs in the chloroplast especially in the thylakoid membrane. Light reaching the membrane meets two significant parts called photosystems, PSI and PSII. Every PS comprises of a Light-Harvesting Complex and Reaction Center Complex. The reaction center complex comprises of an electron acceptor molecule, chlorophyll, and proteins. The light harvesting complex comprises of several carotenoids, chlorophyll B, chlorophyll, and proteins.
In stage II or the Calvin Cycle carbon produced from CO2 uses chemical energy in NADPH and ATP to process glucose.
The Calvin Cycle occurs in the external parts of the thylakoid membrane, a fluid substance called stroma. The stage comprises of three precise steps; CO2 fixation, RuBp formation, and reduction in organic contents to create G3P (Hopkins et al., 2006). During carbon fixation, CO2 molecule gets incorporated in an organic substance. The organic substance merges with RubP, a 5 carbon sugar. The resulting amalgamation occurs with the assistance of Rubisco, a protein. The formed 6 carbon molecule is broken into a 3 carbon molecule. By the use of NADPH and ATP, the resulting organic molecule turns into G3P, the resulting photosynthesis product. According to Hopkins et al., (2006) the resulting product is actually the foundation of all carbohydrates and is a 3 carbon sugar. Every cycle identified needs 3 carbon dioxide molecule in addition to three RuBp molecules summing up to a total of eighteen carbons. Every G3P molecule is made up of three carbons, making a total of six G3P molecules resulting from the cycle spins. However, only one net gain of G3P is achieved as the remaining substances are used up by ATP to revamp RuBP. Thus, creating 1 molecule requires six carbon dioxide molecules, 6 RuBP, NADPH, and 18 ATP’s.
The two stages take place in the Chloroplast. These are organelles present in the cells of algae and plants.
Cellular Respiration
Cellular respiration includes the totals of all numerous biochemical means which eukaryotic organisms apply in extracting energy from food particles mostly glucose. Hopkins et al., (2006) maintain that the entire cellular respiration procedure entails four major steps that include; Glycolysis that take place in all living organisms, the eukaryotic and prokaryotic, the bridge reaction that prepares for aerobic respiration, and finally, electron transport chain and the Krebs process. The last two stages depend on oxygen occurring in the mitochondria.
According to Hopkins et al., (2006) the above mentioned steps do not take place at the same rate. They also do not set reactions at the same rate. For example, during a cellular respiration, the Krebs cycle may be undertaking a different stage while the bridge reaction is setting up a different reaction at a totally different speed within the same organism. At the same time, during glycolysis, muscle cells expectation would be that intense anaerobic exercise is underway occurring on an oxygen deficiency. However, the phases of aerobic respiration do not increase unless a physical activity is undertaken at an aerobic force level.
Cellular Respiration Equation
The whole cellular respiration equation is dependent on one source to another. For instance, many authors and scientists prefer to add meaning full products and reactants. For instance, several sources leave out the electron carrier NADH/NAD+ and FAD2+/FADH2 (Hopkins et al., 2006). Otherwise the 6 carbon sugar molecule glucose I changed to CO2 and H2O in the presence of O2 to give thirty six to thirty eight molecules of ATP.
C6H12O6+6O2 – 6CO2+12H2O+36 ATP
Glycolysis
Glycolysis entails a process of a 10-enzyme catalyzed reaction. Glycolysis is the very first stage of cellular respiration. The phase is known as the metabolic pathway where glucose (C6H12O6) is converted to pyruvate (CH3COCOO-+H+). Energy produced in the stage is utilized in forming high energy ATP molecules (adenosine triphosphate) in addition to NADH also known as “reduced nicotinamide adenine dinucleotide) It is set on 10 reactions that do not need oxygen. Thus it takes place within every living organism (cell) (Hopkins et al., 2006). Prokaryotes also called “archaebacteris makes use of glycolysis entirely. On the other hand, aeukaryotes (that include plants, protists, fungi, and animals) utilize it as a table setter. According to Hopkins et al., (2006) the stage takes place within the cytoplasm. Also called the investment phase, 2 ATP are used up as in the process 2 phosphates add to the glucose derivative. Thereafter, it is split into 3-carbon parts (compounds). They are later moved into pyruvate, 2 NADH and 4 ATP to gain two ATP.
The Bridge Reaction
The Bridge reaction is a minor process but very critical. As the name suggests, it is just a bridge or transition to the remaining part of the cellular respiration process. The reaction takes place at the mitochondria whereby the molecules from the glycolysis are changed to 2 molecules that comprise of coenzyme A (acetyl CoA) together with the 2 molecules resulting from the carbon dioxide from the metabolic remains. At this stage, ATP is not produced (Hopkins et al., 2006). At this stage the reaction that entails oxidative decaboxylation within the respiration is an important processing stage whereby stringent anaerobic changes in the glycolysis in which two phases of aerobic respiration taking place within the mitochondria. The stage is also called pyryvate oxidation.
Two steps are involved in the bridge reaction; the decarboxylation and attachment to coenzyme molecule A. The resulting bridge reaction is;
2CH3C(=O)C(O)O-+2 CoA+2NAD+ - 2CH3C(+O)CoA+2NADH
The Krebs cycle
During the Krebs cycle, little energy is generated (only 2 ATP). However combining the 4 carbon molecule oxaloacetate and the 2-carbon molecule thereafter cycling the results by way of various transitions which lean the molecule to its oxaloacetate state, it produces 2-FADH2 and 8-NADH, which is an electron carrier (Hopkins et al., 2006). The resulting molecules are critical for the transportation of electron chain. The outcome entails as discussed above (carriers) are necessary for the next phase. During the process, 4 extra carbon dioxide molecules are released from the resulting waste.
The Electron Transport Chain
The Electron Transport Chain is the final and fourth stage. It is where majority of the energy is created. The electrons (carrier FADH2 and NADH) are extracted by the mitochondrial membrane molecules necessary for the oxidative phosphorylation process (Hopkins et al., 2006). Herein, an electrochemical gradient released by the FADH2 and NADH carriers are added to the phosphate molecules producing ATP. At this step, oxygen is very much required since it is the last electron acceptor along the production chain (Hopkins et al., 2006). It produces water, H2O. It is here that water is created within the cellular respiration. A total of thirty two to thirty four molecules are produced during this phase of cellular respiration. In total, thirty six to thirty eight ATP are generated here. That is; 2+2 + (32or 34) (Hopkins et al., 2006). This is the total sum of numerous biochemical processes employed by eukaryotic organisms in extracting energy from food particles, mostly glucose molecules.
Photosynthesis and cellular respiration are the essence of life. They provide the energy needed by living organisms to undertake all functions in life. Organisms that are single-celled however need very minimal energy and only live on fermentation and glucose. It is also a critical process is energy produced cannot be utilized unless kept in ATP. Cells within the living organism on the other hand depend on ATP to get the energy to undertake all their respective activities. Cellular respiration gives cells the protection they need to keep away from dangerous temperatures. On the other hand, photosynthesis is the source of all oxygen needed by organisms in the environment. The process also enables carbon cycle around the plants, oceans, animals, and earth thus contributing to the unique relationship between animals, humans, and plants. Finally, it serves as the principal energy course for most plants and trees, thus creating a unique relationship with cellular respiration.
Reference
Hopkins, W. G., Archer, M. D., Barber, J., Metzler, D. E., & Butler, M. (2006). Photosynthesis and Respiration. Retrieved from https://id.b-ok.org/book/648851/b3c10e/
