Introduction
Cellular energetics are types of ways in which cells, whether eukaryotes or prokaryotes, obtain energy to drive functions in a cell. Cellular respiration is one type, for eukaryotes, that uses reactants like sugar, such as glucose, and oxygen to create products of carbon dioxide, water, and energy in the form of ATP (Urry et al 2020). The purpose of this process is to create energy for the cell’s functions, water for the body, and carbon dioxide that is useful in the role of photosynthesis. Photosynthesis is an autotroph’s way of creating oxygen and energy by using the reactants, carbon dioxide, light energy, and water (Urry et al 2020) Autotrophs are organisms that obtain organic food molecules without eating other organisms or substances derived from other organisms while heterotrophs use organic food molecules. This circle of reactants and products between cellular respiration and photosynthesis is a necessity for energy creation.
Cellular respiration does not only have to use glucose but can use a means of many sugars. Glucose is found in common foods, therefore is used as the example. Glucose, galactose, and fructose are all monosaccharides, while lactose and sucrose are disaccharides, and honey is a polysaccharide (Urry et al 2020). Some sugars are used more readily by yeast than others. This illustrates enzyme regulation call induction. This process occurs when the cells of yeast, usually grown in the presence of one type of sugar, experience the absence of the food it usually encounters. If it is fed an alternative energy source for which the cells maintain no enzymes, it takes some time for the yeast to induce expression of genes for the new enzymes it needs. You can tell this is happening if you observe a lag time in respiration while the yeast is involved in producing sufficient enzyme for there to be an increase in respiration time.
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Since photosynthesis does not use sugars as an energy source, another mean has to be used. Plants are often found in the outdoors as is light. This light energy can be, and often is, produced by the sun. Photosynthesis can be divided into two sets of reactions: light dependent and light independent. Light dependent reactions are nearly instantaneous and captures the light to use for an autotroph’s own chemical energy. Light independent is slower but uses electron and protons from NADPH to reduce carbon dioxide and uses that ATP energy to form new bonds (Urry et al 2020). A visible spectrum is the primary part of electromagnetic spectrum because it’s the only part seen by the human eye. It includes electromagnetic radiation whose wavelength is between 400 nanometers and 700 nanometers. Visible light from the sun appears white, however, it is made up of wavelengths of light, known as colors. The various wavelengths in sunlight are not all used the same in photosynthesis. Photosynthetic organisms contain light-absorbing molecules called pigments, found in chlorophyll. It absorbs certain wavelengths of visible light, while reflecting others. The set of wavelengths absorbed by a pigment is its absorption (Urry et al 2020). Chlorophyll-b best absorbs blue light and chlorophyll-a best absorbs red light.
Cellular respiration is split into three steps. Glycolysis is the process of breaking down sugars to two three-carbon pyruvates. Sugar is broken using two ATP. Some sugars accept phosphates more readily than others. Adenosine triphosphate (ATP). is most often the source of the phosphate group. It has a net gain of 2 ATP and 2 NADH (Urry et al 2020). Glycolysis is regulated by phosphofructokinase. This is a kinase enzyme that phosphorylates fructose 6-phosphate in glycolysis (Urry et al 2020). If oxygen was present the Krebs cycle could be carried out. This second step is where 2 acetyl CoA, a 4 carbon acceptor molecule that powers the cycle, 8 NAD+ and 2 FAD that will become electron carrier molecules, and 2 ADP + P that will become 2 ATP, and 6 O2 that provide necessary oxygen, making the Krebs cycle aerobic. The Krebs cycle is regulated by the concentration of ATP and NADH. The electron transport chain is the following step if oxygen is present. The ETC uses 10 NADH electron carrier molecules 2 from Glycolysis, 8 from the Krebs Cycle, 2 FADH (from the Krebs Cycle), plus the 6 oxygen atoms from the original glucose molecule, and, most importantly, 34 ADP to P that are waiting to be combined by the ATP synthase (an enzyme that makes ATP) (Urry et al 2020). The electrons from the electron carrier molecules go down the electron transport chain and the H+ ions from the electron carrier molecules to go across the inner membrane through active transport, then they charge back out through facilitated diffusion through the ATP synthase (Urry et al 2020). The ETC is regulated by levels of ADP and ATP, and many other enzymes are subject to regulation.
There are two types of cellular respiration aerobic, with oxygen, and anaerobic, without oxygen. Fermentation is a way to create ATP without oxygen. It is completed as the second phase in cellular respiration if no oxygen is present. The pyruvate, products of glycolysis, decides where to go after glycolysis, the first step, dependent upon if oxygen is present. In yeast, the extra reactions make alcohol, while in your muscles, they make lactic acid. In fermentation, the pyruvate made in glycolysis does not continue through oxidation and the citric acid cycle, and the electron transport chain does not run. Because the electron transport chain isn't functional, the NADH made in glycolysis cannot drop its electrons off there to turn back into NAD+. The purpose of the extra reactions in fermentation, then, is to regenerate the electron carrier NAD+ from the NADH produced in glycolysis. The extra reactions accomplish this by letting NADH drop its electrons off with an organic molecule (such as pyruvate, the end product of glycolysis). This drop-off allows glycolysis to keep running by ensuring a steady supply of NAD+.
The first step of photosynthesis, also known as the light dependent take place in the thylakoid membrane and requires light energy. Chlorophylls absorb this light energy in photosystem I and photosystem II, which is converted into chemical energy through the formation of two compounds, ATP and NADH, which is created in the ETC. In this process, water molecules are also converted to oxygen gas. The Calvin Cycle, also called the light independent reaction, takes place in the stroma and does not directly require light. Instead, the Calvin cycle uses ATP and NADH from the light-dependent reactions to fix carbon dioxide and produce three-carbon sugars that combine to form glucose.
Sugars are simple carbohydrates. They are occasionally referred to as saccharides, which come in two forms: monosaccharides and disaccharides. Monosaccharides have the chemical formula C6H12O6 while Disaccharides have the chemical formula C12H22O11 (Urry et al 2020. These are not the only two configurations that exist. The multiple configurations of atoms are called isomers. Isomers of saccharides are necessary due to organisms have evolved enzymes to create the energy in each form. Some organisms, including yeast, are better at getting at some forms of sugar than other forms because of the enzymes that they can use (Urry et al 2020). The monosaccharides will have a high cellular respiration rate because the monosaccharides can break down faster due to its mass being smaller. On the other side of energy creation methods, photosynthesis will be processed faster with red and blue filters due to these mirroring the wavelengths.
Purpose and Methods
Two experiments were completed with similar procedures. Experiment one used 7 large test tubes, 7 rubber stoppers, 7 graduated pipettes, sugar solutions (glucose, fructose, lactose, galactose, sucrose, honey, and water), and 70 mL active yeast (University et al 2018). The primary experiment began by collecting and stirring the stock yeast culture. This released any air bubbles present. Next, 10 mL of the yeast was pipetted into each of the seven large-diameter test tubes and then capped the tubes with their own rubber stopper and pipette, making sure to mark the initial point on a table. Following this, a set volume of the sugar solutions was added to the 6 separate test tubes. The seventh test tube was filled with distilled water, rather than a sugar solution to act as a control. Each tube was filled approximately ¼ below the rim of the tube. Once the solutions were presented in the pipettes, a record was taken for the starting volume. After 5, ten-minute intervals, an observation was taken, to track the rate at which O2 was created. In this experiment the controls were the yeast used. The independent variable in the initial experiment was the sugar solution used. The dependent variable was the amount of carbon dioxide produce or another way of phrasing it is, the rate of fermentation.
Experiment two used four large colored test tubes (red, blue, green, and yellow), an uncolored test tube, 10 mM sodium bicarbonate (pH 7), a strong light source (powered lamp), rubber stoppers with graduated pipettes, and Elodea stalks (University et al 2018). Five large diameter test tubes were filled nearly to the top with sodium bicarbonate, approximately ¼ inch below the rims of the test tubes. A stalk of Elodea was added to each test tube. A pipetted rubber stopper was placed on top of each to cap the liquid. A small amount of solution was transfer up the pipette once the stopper was properly placed. Next, a mark was made to recall the initial place of the sodium bicarbonate in the pipette. The solution over spilled, therefore, a transfer of excess had to be completed until the pipette read at or below 1/3 of the pipette’s entire length. The test tubes were set equal distance from a light source. Every ten minutes, a record was done of the volume the pipette read. The control in this experiment includes the sodium bicarbonate, the stalks of elodea, and the light source. The independent variable is the filters. The dependent variable in experiment two is the oxygen gas or the rate of photosynthesis.
Discussion
The cellular energetics are complex when seen up close, however, when allowing it to be seen through experiments breaks it apart and shows the basics. The hypothesis is the monosaccharides will have a high cellular respiration rate because the monosaccharides can break down faster due to its mass being smaller as seen by the chemical formula, C6H12O6. Yeast is best at digesting glucose and fructose because it is a monosaccharide, both sharing the chemical formula, C6H12O6. Photosynthesis proceeded faster with red and blue filters due to these mirroring the wavelengths. The wavelengths depict exactly what the hypothesis and the experiment did. The red and blue filters created the fast rate of photosynthesis due to the wavelengths. Results may not depict hypothesis due to human error, however, this one followed. Such human error for the second experiment can include the test tubes were hand painted and the light behind was created synthetically.
Dieting is important and has a substantial impact on cellular metabolic processes that sustain life. Chemical energy is stored in the foods we eat through sugars known as carbohydrates, protein, and fats (Foster 2019). Many autotrophs that undergo photosynthesis create glucose that can be consumed by heterotrophs for energy. A diet full of fruits and vegetables is beneficial to one’s health. Without these types of food an increased risk of cardiovascular disease, digestive disorders and types of cancer (Tremblay). Those carbohydrates are broken down through cellular respiration to make energy in the form of ATP (Foster 2019). Glucose is split into two pyruvate using two ATP, however when NAD+ is oxidized to NADH two ATP are formed. Those two ATP and NADH are delivered to the final step. However, the two pyruvates are oxidized creating two acetyl CoA. During the pyruvate oxidation, two additional NADH are created and shipped to the final step, as well as two CO2. The acetyl CoA is used as an enzyme to catalyze the Krebs cycle. Eight NADH and two FADH2 are sent to the final step, the electron transport chain, and four CO2 and two ATP are created for cell use. The twelve NADH and two FADH2 help shuffle protons down the ETC to the top of the ATP synthase (Tremblay). ADP and the protons are combined and sent through to create approximately 32 ATP. Certain products are marketed as dietary supplements however are causing more harm to the body (Tremblay). Dinitrophenol, DNP, is one of these products and can cause substantial weight loss (DeSimone, et al. 2011). This is due to the drug increasing production of cellular respiration and the rate of CO2 produced. DNP disrupts the electron transport chain by altering the proton gradient causing ATP to be low. The human body pulls energy from the bodies previously made fats as an energy source. Glycolysis continues however, creating an abundance of pyruvate which makes acetyl CoA. Acetyl CoA is responsible for breaking the fats for energy (DeSimone, et al. 2011). Just because something is marketed as a diet does not mean it is healthy for the body.
Bibliography
- DeSimone, S. M., & Prud’homme-Généreux, A. (n.d.). 2011. Wrestling with Weight Loss: The Dangers of a Weight-Loss Drug. Retrieved from http://sciencecases.lib.buffalo.edu/cs/files/dnp.pdf.
- Foster CR, Lee KW. 2017. The role of protein structure in Alzheimer’s disease. Journal of the Brain 208(17): 82-92
- Tremblay, S. (n.d.). Food Sources of ATP. Retrieved from https://www.livestrong.com/article/359257-food-sources-of-atp/.
- University, E. T., Miller, H., Foster, C., Jones, T., Wagner, A., & Yampolsky, L., (2018). Biology 1111: biology for science majors laboratory i.: Kendall Hunt
- Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & Campbell, N. A. (2020). Campbell biology in focus (third). Hoboken, NJ: Pearson.
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