In the lab the relative volume of O2 consumed by germinating and non-germinating peas at room temperature and 10°C was determined. The central purpose was to find the affect of germination and temperature on the rate of cellular respiration. The results indicated that the respirometers that contained germinated peas had a greater rate of cellular respiration compared to those with non-germinating and showed that cellular respiration was faster at 10°C. The experiment demonstrated the affect of environmental factors on cellular respiration.
The general questions for the lab involve the affect of environmental factors such as temperature and germination of seeds on cellular respiration. The experiment was performed to discover the affects of temperature and germination on the pea, Pisum Savitum during respiration. The hypothesis predicted says the rate of cellular respiration would be greater in germinating peas verses in non-germinating peas because the dormancy of the non- germinating seeds would result in less oxygen consumed. The prediction for the affect of temperature on cellular respiration says that hotter the temperature, the faster the rate of consumption because as the temperature increases the molecules will move more slowly causing the interactions to be more frequent producing more CO2
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Cellular Respiration is a key way that a cell gains energy. Organic compounds release energy in cellular respiration using O2. This takes place in the mitochondria of a cell. Energy of food molecules is freed and made into ATP. Fats, Proteins, and Carbohydrates are all sources of fuels. Glycolysis, the Krebs Cycle, and oxidative phosphorylation are the three metabolic processes that make up cellular respiration. When O2 is not present, respiration occurs in only glycolysis and fermentation. In glycolysis, glucose breaks into two pyruvates producing two ATP molecules and two NADH molecules. Next is the Krebs cycle where a bundle of chemical energy is produced. The pyruvate is transferred into the mitochondria where it loses carbon dioxide forming acetyl-CoA. This molecule is oxidized to carbon dioxide releasing chemical energy and staying in the form of FADH2, NADH, and ATP. Then the energy stored in NAD+ and FAD is released. The released energy is ATP. In cells lacking oxygen, pyruvate is oxidized by fermentation after glycolysis. Fermentation regenerates NAD+ by oxidizing the NADH produced in glycolysis. About 36-38 molecules of ATP are generated by glucose in aerobic respiration compared to only two in anaerobic respiration. Cells control reaction rates in response to changes in metabolic needs. When their products are sufficient in supply anabolic pathways are shut off. Feedback inhibition is the most common mechanism. Glycolysis and the Krebs cycle are controlled by regulating enzyme activity at certain points. The third step of glycolysis is a key point in catabolism which is catalyzed by a key enzyme called phosphofructokanse. As its concentration rises, it slows down glycolysis. As the rate of glycolysis slows the Krebs cycle also slows since the supply of acetyl-CoA is reduced. ADP and AMP are allosteric activators for phosphofructokinase so when their concentrations (relative to ATP) the enzyme speeds up glycolysis which speeds up the Krebs cycle.
This experiment involved seeds that were living but also dormant. A seed is dormant if it is in a state where it is prevented from germinating in all conditions. The non-germinating seeds we used were dormant. Germination begins when warmth and moisture conditions are favorable. Most seeds contain a plant embryo and an initial food supply which are protected by a seed coat. Environmental condition ns such as gases, temperature, light, and mechanical restrictions which are usually favorable for germination do not germinate a dormant seed. In the experiment, germination will begin when the seeds are soaked. The enzymes begin to use to stored food supply to make ATP which increases the rate of cellular respiration. The complete oxidation of glucose is shown in the equation by this equation: C6H12O6 ïƒ 6CO2 +6H2O +686 kilocalories of energy/mole of glucose oxidized. Oxygen is required for this energy releasing process to occur. Cellular respiration can be determined by the consumption of O2, the production of CO2, and the release of energy during cellular respiration. In this experiment, the relative volume of O2 consumed by germinating and non germinating peas will be measured.
The apparatus used in the experiment can be explained by gas laws. PV=nRT is the general gas law. P stands for the pressure of the gas. V stands for the volume of the gas. N stands for the number of molecules of gas. R stands for the gas constant. T is the temperature of the gas (K). The law suggests four concepts about gases. The first law states that if the pressure and temperature are kept constant, then the volume of the gas is directly proportional to the number of molecules of the gas. The second states that the pressure and molecules of gas are proportionate if the temperature and volume are unchanged. The third states if the amount of gas molecules and the temperature remain constant, then the pressure is inversely relative to the volume. The fourth is if the temperature changes and gas molecules are kept constant, then either the pressure, volume, or both will change in direct proportion to the temperature. Both gases and fluids flow from areas of high pressure to regions of low pressure. In the experiment, potassium hydroxide will remove the CO2 formed during cellular respiration. This will form solid potassium carbonate (K2CO3) shown by CO2 + 2KOH ïƒ K2CO3 +H2O. Because CO2 is removed, the change in the volume of gas in the respirometers will be directly related to the amount of oxygen consumed. In the experiment apparatus, if H2O temperature and volume remain constant, the water will move toward the region with lower pressure. Oxygen is consumed during respiration. Its volume is reduced, because the CO2 produced is being converted to a solid. The net result is decrease in gas volume within the tube and a related decrease in pressure in the tube. The vial with glass beads alone will show any changes in volume due to pressure, atmospheric, or temperature changes. A respirometer measures the rate of exchange of either carbon dioxide or oxygen. It is used to determine the rate of respiration for a living organism.
Materials and methods
100 mL graduated cylinder
20 dried peas
20 germinating peas
Six vials with fastened stoppers and pipettes
-Carolina Biological Potassium Hydroxide 15% 150 mL for KOH 2006
Piece of paper
-Item No: SC2020
-Capacity: 200 X 0.01g
-Power: +6 to 12 VDC 70m A max
-Battery req: 1 av alkaline
Dry Peas, 1 lb.-
manufacturer: Carolina Biological
model # 158863
AP Biology Lab 5: Cellular Respiration Lab Activity
manufacturer: Ward’s Natural Science
model # 36 V 7104
Begin by setting up a 10°C bath to allow time for the temperature of the water to adjust. Add ice and an ice pack to attain a temperature of 10°C. Then fill 50mL of water into a 100mL graduated cylinder. Put 20 germinating peas in the cylinder and measure how much water was displaced. The quantity of H2O moved should equal the peas’ volume. Record the volume of the 20 peas. Then remove the peas and place them on to a paper towel. Fill the graduate cylinder with 50 mL. Drop 20 non-germinating. Put in glass beads until a volume equal to the germinating peas’ volume is reached. Take out the peas and put them on to a paper towel. Then fill the graduated cylinder with fifty mL of H2O. Drop glass beads until a volume equal to the volume of the germinating peas is reached. Then take out these peas and put them on a paper towel. Then put together three respirometers. Get three vials attached with a pipette and stopper. For each vial, put a tiny piece of cotton and put five drops or until moistened onto cotton of 15% KOH. On the top of each KOH-soaked absorbent cotton, place a small wad of nonabsorbent cotton. Then, place the first three sets of beads into the first thee vials. Place in the fitted stopper. Put a weighted collar on every end of the vial. Then place the first three vials into the 10°C water bath. Make sure that the pipettes did not touch the H2O for the seven minute equilibration. After seven minutes, submerge the three respirometers into the baths, covering them complete with water. Place a sheet of paper underneath to make the amount of water entering the pipette easier to see and measure. Position the pipettes to ensure they can be read clearly. Let the respirometers equilibrate for three additional minutes and then record the initial position of H2O in every pipette. Check the temperature in both baths and record them. In 5 minute intervals up to 20 minutes take measurements of the water’s position in each pipette and record the data.
The results showed a general trend of increase in the concentrated difference of the peas. Most of the results accurately showed the affect of germination and temperature on cellular respiration. The rate of the Germinating Peas was the quickest. The group data for the non-germinating peas was not accurate because the amount of oxygen was reduced (Graph 1). However; the group data for the germinating peas showed a linear trend of increase. Because the temperatures varied we corrected the differences in volume that were due to temperature instability rather than the rate of respiration by finding the corrected difference. Corrected difference was found by subtracting the change in the transition of H2O into the vial with glass beads from the experimental vials, held at the equal temperature. Therefore our results showed an accurate affect of temperature.
The Results supported the hypothesis predicting the affect of germination on the rate of respiration. The respirometers with germinating seeds had a faster rate of cellular respiration in both room and 10°C temperature compared to the respirometers containing non-germinating seeds (Table 15). The non-germinating peas took in less O2 compared to those germinated which can be seen by Graph 1 and 2, causing cellular respiration to occur more slowly. This happened because germinated seeds need more oxygen to continue to survive and grow even though germinated and non- germinated seeds are both alive. In the lab, the carbon dioxide made by cellular respiration was removed by Potassium Hydroxide which created Potassium Carbohydrate. The difference in the volume of gases in the respirometers was proportional to the quantity of oxygen consumed due to the oxygen being removed. What was predicted of the affect on temperature on respiration did not occur. The rate of respiration was not higher at room temperature compared to at 10°C. This may be due to the peas being adapted to harvesting. Peas are a cool weathering crop, so they do not harvest best at hotter temperatures. The peas therefore are adapted to cooler temperature accounting for the rate of cellular respiration being higher in 10°C.
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There were possible errors that may have occurred in the experiment. Any of the respirometers could have leaked due to the seals not being completely air tight causing gas to escape. The amount of cotton in each vial was an estimate which could have affected the transformation of CO2 into a solid. The peas came in contact with the KOH which may have affected the transformation of CO2 into a solid. Moving the vials and putting your hands in the water could have caused contamination. The timing for the five minute timer intervals and equilibration period may have had errors affection the amount of oxygen consumed. Improvements in the lab could be made by taping the respirometers onto the bath to prevent movement. Also by having more ice and also crushing the ice instead of using cubes to help keep the water temperature more constant. Some extensions for the lab could be to measure the rate of cellular respiration with different types of peas. Also the affect of other environmental factors such as light intensity and pH could be tested. This lab effectively showed affect of temperature and germination on cellular respiration using the pea, Pisum Sativum.
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