Cellular Respiration And the Lord God formed man from the slime of the earth; and breathed into his face the breath of life, and man became a living soul. Genesis 2:7 Introduction Note: This experiment will require two days to complete. Cellular respiration refers to the process by which eukaryotic cells convert chemical energy existing in organic molecules (such as glucose) into an energy form which can be used by the cell. Adenosine triphosphate (ATP) is the energy form used in most cellular processes. The overall formula for cellular respiration is: Today, we wish to investigate levels of cellular respiration being performed in beans. Although we use beans as a food, they are also seeds that begin cellular respiration upon germination. Germination is the budding of a seed when exposed to the proper conditions after having remained dormant for some period. Beans and other seeds store glucose specifically for the developing bud and plant embryo. The ideal temperature range for pea seed germination is between 10 o C and 30 o C (50 o F and 86 o F). Reviewing the chemical equation above, how could we examine cellular respiration in germinating beans? The strategy could involve measuring the disappearance of either glucose or oxygen as they were being consumed by beans over a certain time. Or, one could measure the production of CO2, H2O or ATP by the beans over a time. In today s experiment, we will determine respiration by detecting CO2 production in germinating beans and comparing it to respiration in non-germinating beans. A liquid ph indicator made from red cabbage leaves will be used to test the production of CO2. As CO2 gas is produced from cellular respiration, it reacts with the water vapor in the air, forming carbonic acid and acidic conditions. The red cabbage ph indicator changes color as the ph conditions change from neutral to acidic or basic. If we place the red cabbage liquid ph indicator along with the beans in a closed system, we should be able to evaluate the levels of CO2 production. Learning Objectives: Compare CO 2 production between germinating and non-germinating beans Relate production of CO 2 to cellular respiration Safety Although the red cabbage liquid ph indicator is not caustic, wear gloves when handling as a good laboratory practice and since some may be sensitive to the juice. The red cabbage liquid will stain clothing and some countertops. Wear appropriate clothing and clean spills immediately. 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 1
Materials Required: From Biology Kit Student Supplied Test tubes Beans, dried, any small variety Test tube rack Red cabbage, a few leaves Graduated cylinders (10 and 100 ml) Cotton balls (3) Pipette Distilled water, 2 cups (NOT TAP WATER) Beaker Plastic wrap Measuring cups 3 household items to test (lemon juice or vinegar; hand or dish soap; window or kitchen cleaner) Clear glasses or plastic cups, small (2) Straw Experiment Preparation Day 1 1. Prepare Beans Place 10 beans on a paper towel for 24 hours Place 10 beans in a glass covered with distilled water for 24 hours It is advisable to pre-soak 2-3 extra beans Beans that float will not germinate and should not be used Keep both in a warm place (between 70 o F and 86 o F) and undisturbed for 24 hours 2. Prepare Red Cabbage Liquid ph Indicator Cut several leaves of a red cabbage into small pieces and place in a pan Cover cabbage with 2 cups of Distilled Water (NOT TAP WATER) Bring the mixture in pan to gentle boil and steep the leaves for about 10 minutes Filter the leaves from the liquid with a kitchen strainer Retain the liquid this will be the Red Cabbage Liquid ph Indicator Some of the liquid will be used in Steps 3 and 4 below Store the remainder in an air-tight container in the refrigerator for the Day 2 experiment Discard the leaves Liquid should be a neutral blueish color 3. Use Red Cabbage Liquid ph Indicator to Detect CO2 Measure 50 ml into each of two small, clear glasses or plastic cups Label one cup Control and one CO 2 Breathing Exp. In Table 1, record the starting colors, ph and acidity levels of the ph Indicator in each cup Take a straw and exhale into the cup labeled CO 2 Breathing Exp. Do not drink the indicator, but blow INTO it Continue to blow into the solution for 10 minutes, or until a color change is evident Pour 5 ml of this solution into a test in order to visualize the color better Pour 5 ml of the Control solution into a second test tube Compare and Contrast Record the colors of the Control and CO 2 Breathing Exp. solutions in Table 1 Note, the Control has not been treated, so there should be no change Using the chart, identify the approximate ph and acidity level of the Control solution and record in Table 1 Identify the approximate ph and acidity level of the CO 2 Breathing Exp. solution and record in Table 1 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 2
Use the remainder of the Control solution in Step 4 Discard the CO 2 Breathing Exp. sample after recording the colors in Table 1 4. Use Red Cabbage Liquid ph Indicator to test ph Place 3 ml of red cabbage ph indicator in each of 3 test tubes In one test tube, use the dropper to place 3 drops of lemon juice (or vinegar or soda) Mix well Read approximate ph and acidity level using the chart Record in Table 2 Note beside table which substance was actually used In another test tube, place 5 drops of liquid dish soap or hand soap; mix, read ph and record In the last test tube, place 1 ml of glass cleaner or kitchen cleaner; mix, read ph and record 5. Answer Data and Analysis Questions 1-5 in preparation for Day 2 Experiment Day 2 6. Remove the Red Cabbage Liquid ph Indicator from the refrigerator and bring to room temperature 7. Carefully, drain excess water from the soaked beans Take care handling the soaked beans since they are fragile 8. Prepare 3 test tubes Place 3 ml of Red Cabbage ph Indicator in each test tube Place a cotton ball in each test tube just above the water line In the Control Test Tube: Simply cover with a piece of plastic wrap In the Dry Beans Test Tube: Place 10 dry beans and cover with plastic wrap In the Soaked Beans Test Tube: Place 10 pre-soaked beans and cover with plastic wrap Note: You do not need to use all 10 beans in the test tube. But, make sure there are the same number of beans in the Dry Beans and Soaked Beans test tubes. 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 3
9. Record Time 0 Information Record the color of each solution in Table 3 Use the ph chart to record the starting ph Place the test tube rack in a warm area in which it will not be disturbed Although not required, you may wish to take a starting photo to compare starting colors to final results 10. Record Information at 1-Hour Intervals Set a timer, and record the following at 1-hour intervals until there are 4-hours of data Color of solution ph of solution Note: If the color falls in between two colors, you may give it a decimal value For example, a color between red and dark pink may be given a ph value of 1.5 11. Perform Data Analysis and Conclusions Clean labware and lab area Put everything in its proper place 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 4
Lab Report for: Control CO2 Breathing Exp. Table 1 CO 2 Breathing Experiment Color of Solution Before Breathing Color of Solution After Breathing ph Acidic, Basic, or Neutral? Table 2 ph Solution ph Neutral, Acidic or Basic? Lemon juice/vinegar Hand/dish soap Window/kitchen cleaner Time 0 hr 1 hr 2 hr 3 hr 4 hr Table 3 CO 2 Production in Seeds Control Dry Beans Pre-Soaked Beans Color ph Color ph Color ph 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 5
DAY 1 QUESTIONS 1. The ph of a solution is a measure of how much acid or base is in that solution. When you tested household materials: a. Which solution(s) had a low ph? b. Which solution(s) had a high ph? c. Which solution(s) was/were acidic? d. Which solution(s) was/were basic? e. Which solution(s) was/were close to neutral? 2. What is a ph Indicator and why is it used in experiments? 3. What gas is produced as a waste product of cellular respiration? What gas is exhaled by the lungs as a waste product? 4. CO2 breathing experiment: a. When CO2 is bubbled into a watery solution, what gas is it converted into? b. When this new gas is in solution does it make the solution acid, neutral or basic? c. Did your results in Table 1 confirm or counter your answer in b? Explain using your data from Table 1 5. If germinating seeds do undergo cellular respiration, what changes would you expect to see in the ph indicator solution? (Hint: Recall the results of the CO2 breathing experiment.) DAY 2 QUESTIONS 6. In comparing the solution in the Control to the solution in the Dry Beans test tube: a. Was there a color change? b. What does this change, or lack of change indicate? Explain your answer. c. Do dry beans undergo cellular respiration? Support your answer using your data. 7. In comparing the solution in the Control to the solution in the Pre-Soaked Beans test tube: a. Was there a color change? b. What does this change, or lack of change indicate? Explain your answer. c. Do pre-soaked beans undergo cellular respiration? Support your answer using your data. 8. Experimental Design: a. In this experiment, we tested for the production of a chemical so that we could evaluate cellular respiration. What was this chemical? b. What solution did we use in order to detect this chemical? c. How did this solution detect this chemical? 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 6
9. In a few sentences, write a conclusion statement regarding cellular respiration in dry beans vs. beans that had been pre-soaked. Make sure to include at least the following words (not necessarily in this order): Control, dry beans, germinating beans, pre-soaked (or soaked) beans, CO2, ph, ph indicator. 10. This experiment was performed at room temperature. What do you expect would the results would be if the same experiment was performed in a greenhouse with tropical temperatures? Explain. 11. A student performs the Cellular Respiration Experiment and obtains the results shown in the figure below. Answer the following: a. What is the purpose of the Control test tube? b. Should there be any change in the Control from Time 0 to Four Hours? Explain. c. Is the experiment valid? Can the results of the Soaked Beans be read and evaluated at Four Hours? Explain. d. What could account for a color change in the Control? e. Why is having a Control not only useful, but necessary? 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 7