Cell Respiration Laboratory PSI Biology

Transcription

1 Cell Respiration Laboratory PSI Biology Name Objective Students will understand the relationship between temperature, pressure, and gas volume and will predict the effect of temperature and germination state of peas on the rate of cell respiration. Materials Each student will need an apron, gloves, and safety goggles. Each group will need the following: 50 dry peas 50 germinating peas 100 plastic (pea-sized) beads 3 Glass vials with metal washers glued on for weight 3 #3 one-hole rubber stoppers 3 1 ml graduated pipets Absorbant cotton Nonabsorbant cotton 1 plastic tray 1 water bath 1 bucket of ice 1 100ml graduated cylinder 1 thermometer Paper towels Marking pen Masking tape Stopwatch or clock with second hand Water Other materials that can be shared: Dropper bottle containing 15% KOH Sealant Time Requirements: Pre-lab prep (For teachers): See teacher notes for pre-lab procedures Lab activity: min. Procedure 1. Take the temperature of the room temperature water bath and record it in Table Label 3 pieces of paper towel as follows: 1a, 2a, 3a. These numbers will correspond to the respirometers with the same numbers. 3. Fill the graduated cylinder with 50 ml of water. 4. Place 25 germinating peas into the water in the graduated cylinder and record the total volume of peas and water inside the cylinder in Table Subtract the initial 50 ml from the final total volume. This is the volume of the germinating peas. Record this value in Table 1 for Respirometer 1a. 6. Pour out the water from the graduated cylinder and place the germinating peas onto the paper towel labeled 1a. 7. Fill the graduated cylinder with 50 ml of water again.

2 8. Place 25 dry peas into the water in the graduated cylinder. Drop plastic beads into the graduated cylinder until the total volume equals the final volume from step 4. This is to make sure that the volume of germinating peas in respirometer 1a and the volume of peas and beads in respirometer 2a are the same. 9. Pour out the water and place the dry peas and plastic beads onto paper towel 2a. 10. Fill the graduated cylinder with 50 ml of water again. 11. Add plastic beads to the water in the graduated cylinder until the total volume equals the final volume from steps 4 and Empty out the water and place the beads on the paper towel labeled 3a. 13. Assemble the respirometers. Label the glass vials 1a, 2a, and 3a. Insert the non-tapered end of one pipet into the upper surface of a rubber stopper. Put a layer of sealant around the junction between the pipet and the rubber stopper. Make sure that there is a weight attached to the vial. Repeat this to make two more respirometers. 14. Place a piece of absorbent cotton in the bottom of each of the vials. Push the cotton firmly into the bottom of the vial. 15. Saturate the cotton in the vials with a few drops of KOH. Make sure you use the same number of drops of KOH in each vial. Do not let the KOH drip onto the sides of the vial. Caution: KOH is caustic. Avoid direct skin contact. Make sure you are wearing gloves, aprons, and goggles when performing this step. 16. Place a piece of nonabsorbent cotton on top of the saturated cotton in each vial and push each piece of cotton to the bottom of each vial. 17. Add the peas, peas and beads, or beads to the appropriate respirometer by placing them on top of the cotton. 18. Place the stoppers on each vial and make sure they are on tight to prevent any leaks. 19. Place a strip of masking tape across the narrow width of the water bath about 2/3 of the way from one end and make sure the tape is anchored firmly on the outside of the pan. The tape will support the respirometers during the equilibration period. 20. Place the three respirometers into the room temperature water bath with the pipets resting o the masking tape. Start timing for a total of 7 minutes. This is the equilibration period. 21. At the end of the equilibration period, completely submerge each respirometer in the water bath. It is normal for some water to enter the pipet but if it should stop quickly. If it doesn t, you need to check for leaks. You should be able to read the volume on the pipets without moving the respirometers. 22. Once the respirometers are submerged, begin timing for 3 minutes. After the 3 minute calibration period, note the position of the water in each pipet and record this in Table 2. This is Time Take further readings at 5, 10, 15, and 20 minutes and record the values in Table Remove the respirometers from the water bath, empty them, rinse them, and dry them thoroughly as you will be reusing them. 25. Add ice to the water bath to lower the temperature to 10 0 C. Periodically check the temperature to be sure it remains constant throughout the experiment. Add ice as necessary to ensure the temperature remains at 10 0 C. 26. Repeat steps 2 through 23 with the remaining peas and beads except that the paper towels and respirometers will now be labeled 1b, 2b, and 3b. Record the data you collect from these respirometers in the appropriate places in Table Calculate the Δ Volume in the pipet at each time interval and record these values in Table 2. To do this, subtract the reading at Time 0 from the reading at each of the subsequent times for each respirometer. 28. Calculate the corrected Δ Volume by subtracting the corresponding correction factor (room temperature or 10 0 C) from the Δ Volume for each respirometer. The correction factor will be found in Table 2. You will plot these data on a graph illustrating oxygen consumption in germinating peas.

3 Table 1 Final volume (ml) Initial volume (ml) Volume of germinating peas (Final Initial, ml.) Temperature of Water Calculation of Germinating Pea Volume Respirometer 1a Respirometer 1b Table 2 Calculation of Oxygen Consumption in Germinating Pea Seeds at Room Temperature and 10 0 C Respirometer 3a: Room Temperature, Beads only (To obtain correction factor) Time interval (min): (Reading Time 0) = Room Temp. correction factor Respirometer 1a: Room Temperature, Germinating Peas (Δ Volume Room Temp. Correction factor) Respirometer 2a: Room Temperature, Dry Peas (Δ Volume Room Temp. Correction factor) Respirometer 3b: 10 0 C, Beads Only (to obtain correction factor) Time interval (min): (Reading Time 0) = 10 0 C correction factor Respirometer 1b: 10 0 C, Germinating Peas (Δ Volume 10 0 C Correction factor)

4 Respirometer 2b: 10 0 C, Dry Peas (Δ Volume 10 0 C Correction factor) Graphing Using the data from the tables, graph the rate of oxygen consumption by the germinated peas and dry peas at room temperature and at 10 0 C. Plot the dependent variable on the Y axis and the independent variable on the X axis. Label each axis and be sure to include the proper units. Don t forget to title your graph. You should have four separate lines on your graph so don t forget to label the lines appropriately or to include a legend. Analysis 1. What was the purpose of using the beads in the experiment? Why did you use the beads only readings for the correction factors? 2. In this experiment, you studied the relationship between temperature, pressure, and gas volume. You should recall that this is the ideal gas law PV = nrt where P = gas pressure, V = gas volume; n = number of gas molecules; R = gas constant; and T = gas temperature (in Kelvin). Identify each part of the ideal gas law with regards to the respirometers. Why did the water move down the pipets in your respirometers?

5 3. If temperature continues to rise, at a certain point we would expect the rate of cell respiration to decline. Why do you think this happens? 4. What do you think would happen to your rate of cell respiration if the environmental temperature dropped to 5 0 C? Why? 5. What do you think would happen to a snake s rate of cell respiration if the environmental temperature dropped to 5 0 C? Why?

6 Teacher notes: Pre-Lab Prep: Two days before the lab, place ½ of the peas to be used in a shallow pan and completely cover the peas with warm water. Cover the pan loosely to prevent the peas from drying out. Allow the peas to soak overnight. The following morning, drain the water from the peas. Saturate several pieces of paper towel with water and wring out the excess. Wrap the soaked peas in the wet paper towels and place them back into the shallow pan. Once again, loosely cover the pan. Let the peas germinate until you are ready to begin the lab activity. Check the paper towels periodically to ensure that they are not drying out. If they are, moisten them again. The day before the lab, fill one shallow pan per group with water and allow them to come to room temperature overnight.