Part B

Measuring Respiration Rates

10. On the paper beneath the capillary tubes, mark the position of one end of each drop of colored water. Note the time. Repeat this procedure every 5 min for 20 min. If respiration is rapid, you may have to reposition the drops as you did in Step 9. In which direction would you expect a drop to move if respiration in the volumeter tube were causing it to move?

11. Remove the paper from the ring stand and use a ruler to measure the distance moved by the drops during each time interval. If you repositioned any drops in Step 10, be sure to add this adjustment when you measure the distances. Enter the measurements in the "Uncorrected" columns in your data table.

12. ^ Clean up your materials and wash your hands before leaving the lab.

Analysis and Conclusions

1. No respiration should have occurred in the control volumeter, which contained only beads. Therefore, any movement of the drop in the control volumeter must have been caused by changes in the temperature of the volumeter jar or the air pressure in the classroom. Since these changes would have affected all three volumeters to the same extent, you must subtract the distance you measured for the control volumeter from the distances you measured for the other two volumeters. Do this calculation for each time interval, and enter the results in the "Corrected" columns in your data table.

2. Each capillary tube has a capacity of 0.063 mL between each 1 cm mark on the tube. Use this information to calculate the volume of O2 consumed by the germinating and nongerminating seeds during each time interval. Enter these results in your data table.

3. Prepare a graph to show the volume of O2 consumed versus time; use different symbols or colors to distinguish the points for the germinating seeds from those for the nongerminating seeds. Make sure each point represents the cumulative volume of O2 consumed. For example, the point plotted for the 15-20 min interval should represent the volume consumed during that interval plus the volume consumed during all of the preceding intervals. Draw the best-fit line through the points for each group of seeds. From the slope of this line, calculate the average rate of respiration in milliliters of O2 per minute for both groups of seeds.

4. Which group of seeds had the higher average rate of respiration? What is the significance of this difference in terms of a seed's ability to survive for long periods?

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