Mr. Barker's Biology Class - Home
Cellular Respiration LabBackground InformationAll life on earth ultimately depends upon the sun for energy. Photosynthesis in plants traps energy from the sun by formation of covalent bonds in complex organic compounds, such as glucose. Organisms release this stored energy by the breakdown of glucose, using a set of enzymatic reactions involving many steps. Breakdown of glucose can occur in the presence of oxygen (aerobically), or in the absence of oxygen (anaerobically). Energy released by the breakdown of glucose is stored in the high energy phosphate bonds of adenosine triphosphate (ATP). Aerobic respiration yields the most energy for organisms, with every mole of glucose producing about 32-40 moles of ATP. Under anaerobic conditions, only 2 moles of ATP are produced. Cellular respiration is the breakdown of organic compounds, resulting in the release of energy. The oxidative breakdown of glucose during cellular respiration produces the energy needed for life in living organisms, as given in equation 1:C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + 32-40 ATPCarbon dioxide (CO2) a by-product of cellular respiration, is required for trapping the energy of the sun by photosynthesis. Photosynthesis results in the formation of glucose, oxygen, and water, as shown in equation 2:6 CO2 + 6 H2O + Sunlight → C6H12O6 + 6 O2The free energy content in the terminal phosphate bond of ATP is 7.3 kCal per mole of ATP. Assuming the synthesis of 38 moles of ATP per mole of glucose broken down during aerobic respiration, a total of 277.4 kCal of energy is stored in the high energy bonds of ATP. This represents about 40.4% of the total free energy released during the breakdown of one mole of glucose. The rest of the energy is lost as heat. Some of this is used to maintain a constant body temperature.This experiment is designed to measure oxygen consumed by germinating peas and non-germinating peas. To measure consumed oxygen, the ideal gas law (equation 3) will be utilized:PV=nRTP = the pressure of the gas, R = the gas constant (a fixed value), V = the volume of the gas, T = the temperature of the gas, n = the number of molecules of the gas.In equation 3, R is always constant. If the pressure of the system (P) and the temperature of the system (T) remain constant, the volume occupied by the gas is directly proportional to the number of molecules of gas.During this experiment, a respirometer will be used to measure the volume of oxygen, and therefore the number of molecules of oxygen, consumed by the peas during cellular respiration. The CO2 released through respiration (see equation 1) is removed from the system by potassium hydroxide (KOH), as shown in equation 4. Therefore the amount of CO2 Gas released does not factor into the analysis and measurement of the amount of oxygen consumed.CO2 + 2KOH → K2CO3 (solid) + H2OThe number of oxygen molecules consumed during respiration by the peas will be directly related to the decrease in the volume occupied by the gas within the respirometer. The water in the pipet will move toward the region of lower pressure, which is created within the respirometer due to oxygen consumption. This assumes constant volume and pressure of the system. The control vial containing the glass beads will be used to measure any change in water volume due to alterations of temperature and pressure. The data will be corrected to reflect these external influences on the respirometer. Experiment ObjectiveThe students will observe cell respiration of germinating and non-germinating peas using respirometers.Materials: Each group will use…3 corks with pipets3 vials with weights glued on the bottomAbsorbent cottonKOH solutionNonabsorbent cotton100 mL graduated cylinderWaterGlass beads20 Germinated peas20 non-germinated peas (2 halves = 1 pea)TrayTape MethodsDetermine the volume of germinated peas:Fill a 100 mL graduated cylinder with 50 mL of water.Add the 25 germinated peas to the cylinder and measure the increase in volume. The difference represents the volume of peas.Volume of water and peas _____________ - 50 mL = ______________ Volume of peasPlace the peas on a paper towel.Determine the volume of non-germinated peas:Fill a 100mL graduated cylinder with 50 mL of water.Add 25 non-germinated peas to the cylinder.Add glass beads to the graduated cylinder until the volume of the water matches the volume recorded for the water and germinated peas.Place peas and glass beads on a paper towel.Determine the volume of glass beads:Fill the 100 mL graduated cylinder with 50 mL of water.Add glass beads until the volume matches the volume of the germinated peas and water.Place glass beads on a paper towels.Setting up the respirometers: Do the following for all of your vials, making them as similar as possible:Place a piece of absorbent cotton (approximately the size of a nickel) into the bottom of each vial- use the large plastic pipet to push it down if needed.Carefully pour 1-2 mL of 15% KOH solution onto the cotton, not allowing it to touch the side walls of the vials.Place a piece of non-absorbent cotton (same size as first piece of cotton) on top of the KOH and absorbent cotton to keep the KOH from touching the peas during the experiment.In each vial, place the following from your paper towels: Vial 1: Germinated peas, Vial 2: non-germinated peas and glass beads, and Vial 3: Glass beads Insert the cork with the pipet sticking up, make sure it is sealed. Only push on the cork portion, the pipet is glass and will break.Wrap a piece of parafilm around the seal so that no water can get into your apparatus.Running the experiment: Stick the vials in the water baths with the pipets resting on the masking tape stretched across the water bath to keep the pipets from going under water. Allow to sit for 5 minutes.While waiting, add a drop of food coloring into the tip of each pipet and place a piece of paper under the pipets in the water. Make a prediction on which peas will have a higher rate of oxygen consumption.Submerge the whole respirometer into the water and arrange them so you can read the markings on each pipet. Water in the bath will enter the pipets and travel a short distance. Once the water seems to stay in one place in the pipet, record your starting measurement. Then take recordings of the pipets every five minutes. Record all data on the data sheet.Cellular Respiration Lab Data SheetPrediction: ____________________________________________________________________TimeGlass Beads OnlyMinutesReadingDifference05101520TimeGerminating PeasMinutesReadingDifferenceCorrectedDifference05101520 TimeDry Peas and BeadsMinutesReadingDifferenceCorrected Difference05101520How to do calculations:Difference column = (initial reading at 0 minutes) – (reading at measured time)Corrected difference column = (Initial reading at 0 minutes – initial reading at X minutes) – (Initial bead reading at 0 minutes- initial bead reading at X minutesResultsGraph only the corrected data for your germinated peas and non-germinated peas. Place time in minutes on your x-axis and volume (mL O2 consumed) on the y-axis. Draw a straight best fit line through the data.Title: ______________________________________________________From the slope of the lines, determine the rate of oxygen consumption of germinating and non-germinating peas. Determine the slope of the lines over a middle section of each line by dividing the difference in the volume of oxygen consumed by the difference in time (ΔY/ΔX).SampleCalculationsRate (Volume of Oxygen Consumed/Time)Germinated PeasNon-germinated PeasLab Report InstructionsEach student will individually write a lab report that includes the following information by Friday December 2nd. This report must be typed and submitted through Schoology, no exceptions. If you need assistance, Mr. Barker will be staying after school Tuesday and Thursday this week or you can email him at barkerm@. Start sooner rather than later so you can get assistance if needed.TITLE AND AUTHORSThe title should describe the experiment and include what we were measuringName of author of the lab reportGroup members: Include the names of all students collaborating on the experimentINTRODUCTIONInclude the question your experiment is designed to answerInclude all relevant background information needed to understand your experimentInclude your prediction- phrase this as “my prediction is…”, this is going to be in the last paragraph of your introductionRESULTSData organized into data tables and a graph is presentAttend to titles, labels, units, and scalesThe graph should be made in excel or google sheets and pasted into your document.DISCUSSIONExplain your results. What data did you obtain? Be sure to state actual data values.Why did you get the results you did? Explain in terms of the question being investigated.Reflect on your prediction. Are your results expected? Explain any anomalies and indicate any errors.Explain how this experiment could be designed better to avoid error. ................
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