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Cellular Respiration vs. Photosynthesis

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Robin Crawford

on 28 November 2012

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Transcript of Cellular Respiration vs. Photosynthesis

Cellular Respiration vs. Photosynthesis Similarities Differences The Relationship Between the Processes Works Cited There are a number of similarities between these two series of reactions such as their equations, transformation of energy, exchange of gases, the Eletron Transport Chain and Chemiosmosis, and the theory of endosymbiosis. Just as there are similarities between cellular respiration and photosynthesis, there are also differences. These differences can include the stage requirements, the use of organic compounds, presence of chlorophyll, and times able to occur. Between photosynthesis and cellular respiration there is what is called an inverse relationship. The two reactions are, as a matter of fact, exact opposites of one another. As stated earlier, the products of one become the reactants to fuel the other. They work in conjunction with each other in that manner. With one process always using the waste products of the other as its reactants and in the end producing the reactants for the second, there is always an abundance of the reactants for either cellular process. Bailey, R. (2011, October 19). www.about.com. Retrieved from http://biology.about.com/od/plantbiology/a/aa050605a.htm

Bailey, R. (2009, February 15). Retrieved from http://biology.about.com/od/cellularprocesses/a/cellrespiration.htm

Bratcher, R. (n.d.). ehow.com. Retrieved from http://www.ehow.com/info_7887257_similarities-between-cell-respiration-photosynthesis.html

manisha. (apri). differences.com. Retrieved from http://www.differencebetween.net/science/difference-between-cellular-respiration-and-photosynthesis/

Science prof online. In (2012). Retrieved from http://www.scienceprofonline.com/metabolism/electron-transport-chain-cellular-respiration.html Let's begin with a brief overview of each Cellular Respiration The equation for cellular respiration is C6H12O6 + O2 = CO2 + H20 + energy All living beings need to get their energy from somewhere. Cellular respiration is used by eukaryotic cells, prokaryotic cells, and by animals. It is, in simple terms, a process whose purpose is to harvest energy from food brought into the person or cell's system. Because it breaks down this food to eventually create energy, called ATP, it is called a catabolic pathway, which literally means to break down. The entire process of cellular respiration can be broken down into three separate stages: Gycolysis (meaning splitting sugars), the Citric Acid Cycle, and the Electron Transport Chain. Glycolysis: Here, the six carbon sugar molecule glucose is split into two three carbon sugar molecules. This initial break down consumes two molecules of ATP and produces two pyruvate (the three carbon sugars), and two high energy eletron carriers called NADH. Glycolysis should also be noted to be able to occur with or without oxygen. Citric Acid Cycle: This stage of cellular respiration is also commonly called the Krebs Cycle. This cycle takes the pyruvate molecules from glycolysis and converts them into a different compound called acetyl CoA. Then by threading this new compound through a series or several steps the cycle produces several NAD (the oxidized form of NADH) molecules, FAD (another high energy electron carrier) and two direct ATP molecules. The NAD and FAD are then reduced in the following few steps so that their reduced forms NADH and FADH2 may carry the electrons onto the next part of cellular respiration. Lastly, it should be noted that the Citric Acid Cycle only takes place in the presence of oxygen but does not directly use it. Electron Transport Chain: This is the only part of cellular respiration that directly requires oxygen. This part of cellular respiration consists of a 'chain' of electron carriers in the mitochondrial membrane of the cell. To be brief, this chain oxidizes the electron carriers NADH and FADH2 that were produced in the Citric Acid Cycle and transfer their electrons to the carrier proteins in the mitochondrial membrane. This carrier protein passes the electrons through the integral proteins embedded in the membrane where they undergo oxidizing reactions. These reactions push H+ ions out and into the mitochondrial intermembrane space where they form a concentration gradient. The final electron carrier, O2, then undergoes ATP synthase and allows the H+ ions to return into the mitochondria, which is where they want to go, through the enzyme ATP synthase. This movement creates a proton motive force and helps to bond ADP molecules with the Pi molecules inside the enzyme to create ATP which can then be used in the organism's daily activities. Photosynthesis The equation for photosynthesis is CO2 + H2O +energy = C6H12O6 + O2 Photosynthesis is the process of taking in the sun's energy and converting it into chemical energy to be stored away in the form of glucose. There are two stages in photosynthesis. They are known as Light Reactions, and Dark Reactions. The Light Reactions. The Light Reactions take place in the thylakoid membrane of the cell's chloroplast. The Dark reactions, while they can take place both in the presence and absence of light, take place in the stroma. Light Reactions: They consist of a something similar to the Electron Transport Chain from Cellular Respiration that is called Chemiosmosis. It is another transport system made of integral proteins with an ATP synthase at the end. The integral proteins for this system are called Photosystem 1 (PS1) and Photosystem 2 (PS2). They are named for the order of their discover, however, not their order in the reactions. This chain of reactions begins when a photon of light strikes the pigment molecules on PS2. This photon energizes the photosystem's electrons, to the wavelength P680. This electron is then transferred to the electron carrier PQ which carries it over to a peripheral protein called the cytochrome complex. However, in order to replace the electron lost on PS2, a water molecule is split into 2 H+ ions, 2 electrons and an O2 molecule. The electrons are taken up by PS2. Moving on, the electron that was being carried by PQ has now reached the cytochrome complex which then passes the electron off to the second electron carrier PC. This carrier takes the electron over to PS1. By this time the electron is no longer in a high energy state and needs more energy to continue onward. This is when a second light photon hits a pigment molecule on PS1 and re-energizes the electron to the wavelength P700. An NADP electron carrier is introduced here and is reduced to NADPH when it receives the electrons. The NADP then passes them off to the ATP synthase which works in much the same way as it did in cellular respiration. Dark Reactions: This consists of the Calvin Cycle; it is very similar in process to the Citric Acid Cycle. The Calvin Cycle can be broken down into three stages: fixation, reduction and regeneration. It begins with the enzyme Rubisco and three 5-carbon RuBP molecules. By drawing in three CO2 molecules and stealing the carbons from them, releasing the O2 back into the environment, the Rubisco enzyme fixates those carbon to the three 5-carbon RuBP. The resulting six carbon molecule is unstable and almost immediately splits into six chains of three carbon 3-PGA. This is called the reduction stage now, as 6ATP molecules and 6NADPH come in and are oxidized to ADP+Pi and NADP to provide the energy needed to convert the 6 chains of 3-PGA to 6 chains of G3P, a slightly different molecule. One of these G3P chains leaves to become energy for the body while the remaining five are to be rearranged to recreate the 3 chains of 5 carbon RuBP from the beginning. It does this by taking the 3 carbons and phosphate group from one G3P and 2 carbons and the phosphate group from a second G3P. These are bonded together to create one chain of five carbon RuBP. That bonding process happens a second time to create the second chain. The leftovers from this process are as follows: five carbons and a single phosphate. However, two phosphates are needed to create a chain of RuBP. It gets this final phosphate from the ADP+Pi molecules formed earlier during the reduction phase. As a result the the Calvin cycle can reproduce its three chains of five carbon RuBP and 3ADP+2Pi molecules. Equations: The similarity between the equations is quite obvious by just looking. They are exact opposites of one another. Cellular respiration uses glucose and oxygen as reactants and makes CO2 and water as products. Photosynthesis uses those products from cellular respiration as its reactants and in turn produces glucose and oxygen- the reactants needed for cellular respiration. Energy Transformation: Both Cellular Respiration and Photosynthesis need to transform energy into different forms in order for their reactions to initially take place and continue onward. Cellular respiration transforms the energy rich molecule gluscose into ATP- an energy source that it can directly use for bodily functions. This ATP gets primarily used in the cell for one of two functions: glycolysis, and the oxidation of pyruvic acid. Photosynthesis does much the same thing when converting light energy eventually into glucose in the two phases known as the Light Reactions and the Calvin Cycle. Gas Exchange: This is a basic component of both cellular respiration and photosynthesis. Without the exchange of gases that takes place in both, these life-giving reactions would not be able to take place. Both processes intake a gas at the beginning. For cellular respiration this gas is O2. For photosynthesis it is CO2. Organisms that use cellular respiration, such as humans, use that oxygen to kick-start and propel the reactions of cellular respiration, especially those occurring during the Electron Transport Chain. At the end of the reaction carbon dioxide is released as a product. Photosynthesis uses that CO2 to propel its own reactions, primarily in the Calvin cycle where it is a required reactant. Oxygen is then released at the end as a product. E.T.C vs Chemiosmosis: They are two very similar processes that take place in cellular respiration and photosynthesis. Both consist of integral and peripheral proteins across either the mitochondrial or thylakoid membranes that work to move electrons through the carrier proteins and create a concentration gradient on one side of the membrane. These concentration gradients both aide create a proton motive force to aide in the production of ATP via ATP synthase. Endosymbiotic Organisms: Both the chloroplast of a plant and the mitochondria of an animal are very important organelles in their respective cells. They play large roles in the processes of photosynthesis and cellular respiration. These organelles, according to endosymbiosis theory are quite likely the remnants of very simple cells that were eaten by more complex cells but were not digested, instead taking root in the complex cell where they are of use by synthesizing energy for the cell to use in much more efficient ways that what could have been used before. Stage Requirements: Both cellular respiration and photosynthesis occur in stages. Cellular respiration occurs over the course of glycolysis, the citric acid cycle and the electron transport chain. Photosynthesis occurs through light reactions (chemiosmosis) and dark reactions (the Calvin cycle). But the requirements to get these stages started are different for each cellular process. The difference lies where you begin sorting the stages. The stages of cellular respiration can be divided based on which ones do require oxygen, and which ones do not. Photosynthesis can be sorted in a similar way but must be split based on which ones require light in order to begin and be completed, and which ones can occur independent of a light source. Organic Compounds: This second difference can be seen in the usage of organic compounds between the two cellular processes. In cellular respiration these organic compounds are used to free up energy for cellular use. In photosynthesis these compounds are used instead for the storage of energy. Chlorophyll: This is a very evident difference between the two processes. In photosynthesis chlorophyll is required in order to help the photosystems absorb the initial light photons so that it can begin synthesizing energy. Cellular respiration does not have this requirement for chlorophyll in order to begin its string of reactions. Times Occurring: In photosynthesis there are times when one reaction, the light dependent reactions, cannot occur. Because they rely on light to take place, and there are times when light just is not available, those reactions will not be able to happen. Cellular respiration on the other hand has no requirement for light. As a result it can occur at any time and place so long as there is a source of oxygen. And to reward you for reading through all that, here's a cute little song I found on youtube about the relationship between cellular respiration and photosynthesis.
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