Cellular Respiration

In this experiment, you will measure the rate of cellular respiration for germinating seeds by measuring the rate of exchange for oxygen. As oxygen is consumed to provide energy, germinating seeds release carbon dioxide. This carbon dioxide is absorbed by potassium carbonate and thus the overall gaseous pressure of the respirometer will be reduced.

The experimental hypothesis is that germinating seeds will show a greater rate of respiration than control glass beads. Additionally, that at higher temperatures, the rate of cellular respiration in the seeds will increase. The null hypotheses are that both glass beads and germinating seeds will display a similar rate of cellular respiration and that temperature has no effect on respiration.

To set up the control, first remove the plunger from a prepared microrespirometer and label it with a CR or CH respectively, depending on whether it is the control room temperature or heated treatment. Add the glass microbeads to each of the microrespirometers up to the 0.5 milliliter mark, and push the plunger in the syringe to the one milliliter mark. Place three to four washers onto the flared end of each microrespirometer to weigh them down while in the water bath.

The microrespirometer will sit capillary tube end up. Finally, set these control devices to the side for the time being. To set up the experimental seated respirometers, remove the plunger from a prepared microrespirometer and label it with ER or EH respectively, depending on whether it is the experimental room temperature or heated treatment.

Measure 0.5 milliliters of germinating seeds into the tuberculin syringe of the microrespirometer. Then, push the syringe to the one milliliter mark. Place three to four washers onto the flared end of each microrespirometer to weigh them down while in the water bath.

To use the microrespirometers, carefully press the CR and ER microrespirometers into the room temperature water bath. The entire syringe should be submerged, but the capillary tubes should be entirely exposed. Remove water from the bath until this position is achieved.

Be sure the top of the capillary tube is open. Perform the same procedure for the CH and EH microrespirometers to set up the higher temperature experimental group. Wait five minutes before moving on to allow the temperature in the microrespirometers to equalize with the water bath.

Add a single drop of manometer fluid to the top of each of the four capillary tubes which seals the microrespirometer chambers. If the chambers are working properly, the manometer fluid will be sucked into the capillary chamber. Use the plunger set in the bath to suck the manometer fluid into the capillary.

Stop when the fluid is about halfway down the capillary tube. It is very important that the microrespirometers are not disturbed once added to the bath. Do not bump the table or insert or remove anything to or from the water bath once the chambers have been sealed and equalized.

Always mark the bottom edge of the manometer fluid that is closer to the chamber. This represents time point zero. Set a timer to sound in five minutes.

After five minutes, create a new mark where the manometer fluid is on each microrespirometer. Repeat every five minutes until 25 minutes has passed or until the manometer fluid has traveled the entire length of the capillary tube. Then remove the respirometers from the water baths.

Measure the distance between each of the marks and record them in table one next to the correct time point. During clean up, manometers should either be deconstructed to be reused or disposed of in the trash. To analyze the data you collected, first plot the data points in graph one with the x-axis as time and the y-axis as the distance the manometer moved, representing oxygen consumption.

Calculate the slope of each line using this equation. Record these values for each microrespirometer in table two. This value represents the amount of cellular respiration that took place over the course of the experiment.

Plot the respiration rates as a bar graph. When you examine this alongside your plot of oxygen consumption, how do your results fit with the hypotheses? Do you see a difference in respiration rate between the control beads and the germinating seeds?

Did increasing the temperature have any effect on the respiration rate?