Cellular respiration is the process that cells use to break down glucose; this releases energy that is used to produce ATP. Cellular respiration involves a series of enzyme-catalysed reactions.
The equation below shows the complete oxidation of glucose during aerobic cellular respiration. Oxygen is required for this energy-releasing process to occur.
C6H12O6 + 6O2 –> 6CO2 + 6H2O + 686 kilocalories of energy/mole of glucose oxidized
By studying the equation above, you will notice there are three ways cellular respiration could be measured. One could measure the:
1.Consumption of O2
2. Production of CO2
3. Release of energy during cellular respiration1
In this experiment the relative rate of CO2 production will be measured. Bromthymol blue (BTB) is an indicator that turns yellow in the presence of an acid. Since CO2 combines with H2O to produce carbonic acid, BTB can be used to detect the presence of CO2.
Since exercising requires more energy than resting, the effect of the cellular respiration of exercise on CO2 production will be tested; the time it takes BTB to turn from blue to yellow will be measured after different time increments of exercising. Since increasing time increment of exercise should require more energy, it is expected that the rate of CO2 production will increase; therefore the time it takes for BTB to change color will decrease.
Research Question: What is the effect on increasing time of exercise on the rate of CO2 production?
The independent variable is time spent exercising
The different levels of the independent variable are 30 seconds, 60 seconds and 90 seconds
The dependent variable is the time taken to change BTB color
The controlled variables include type of exercise, volume of BTB, straw length, color gauged, same timer per test subject, same test subject per trial.
27 test tubes
87 mL of BTB
27 1-mL plastic pipettes
27 10-mL graduated cylinders +/- .1ml
27 straws cut to a length of 10.0 cm +/- .05 cm
27 Lab aprons
27 pair of Safety goggles
1. Have the human test subject rest by sitting in a chair for at least 30 seconds
2. Use a 1-mL plastic pipette to place BTB into a 10-mL graduated cylinder until the BTB reaches the 1-mL mark. Pour the BTB into a test tube.
3. Have the test subject exercise for 30 seconds by doing jumping jacks.
4. Immediately have the test subject exhale normally through the straw into the test tube containing BTB (without immersing the straw in the BTB) and simultaneously start the timer. Record the time in seconds that it takes for the BTB to start to change color. Discard the BTB in the sink and rinse out the test tube thoroughly.
5. Repeat steps 1-4 2 more times, increasing the exercise jumping jacks by
30 seconds each time.
6. Repeat steps 1-5 with 23 more test subjects.
7. To keep controlled variables constant, assign counter to count out loud, measure the same amount/ volume of BTB out, Cut straw length same 27 times.
Class Data Combined
Time taken to change BTB color (seconds)
Time spent exercising Increment One 30 seconds
(+/- .001 seconds)
Time spent exercising Increment Two 60 Seconds (+/- .001 seconds)
Time spent exercising Increment Three 90 seconds
(+/- .001 seconds)
Type of Exercise
Straw Length (+/- .05 cm)
Amount of BTB (+/- .1ml)
The effect of increasing time of exercise increased CO2 production an indicator of increased cellular respiration. This can be observed through noting the time taken for BTB to change color as the time doing jumping jacks increased. As duration of exercise increased, the average time taken for BTB to change color decreased. This is visible because the average time for increment one of 30 seconds was 35.38 seconds while increment two of 60 seconds was lower at 29.69 seconds and finally increment three of 90 seconds was the lowest at 20.68 seconds.
Given there was such a large spread of data and standard deviation was calculated to clarify the distribution of data and also to identify whether any of it overlapped. The error bars appearing on the graph overlap between time increments one of 30 seconds and time increment two of 60 seconds well into each other’s bars showing that while their averages suggest that the two increments are fundamentally different. The spread of data around their mean shows that in fact they are not bring into question the design of this experiment. Overall the graph showed a consistent decline from increment one to increment three backing the assertion that increasing time of exercise also increases CO2 as shown by the faster BTB color change.
Since the error bars between increment one and increment three however did not overlap a t-test was performed in order to identify whether the difference between the two increments was significantly different. Results showed that using alpha level of .05 the average time taken to change the color of BTB of increment one is significantly different from the average time taken to change the color of BTB of increment three. Suggesting that if yet another increment of time was added it would produce even faster color changes of BTB. Although the increased rate of CO2 production does not immediately decrease the time taken for BTB to change color, it does eventually.
The primary source of error comes from the lack of clarity within the procedure. Since time constraints did not allow for enough time to wait until the color of BTB changed into a complete yellow the procedure was modified to any kind of color change. The BTB was dark in color and data was collected with many different subjects with varying degrees of eye sight proficiency and different definitions of what constitutes a color change. This source of error throws off the average of each increment by an unknown amount and gives an explanation as to why the standard deviation is high among all three increments. However because each persons definition was kept consistent between each increment while accuracy is thrown off greatly, precision is still relatively maintained. Additionally procedural error came from step 4 of the procedure where the straw was instructed to be placed in the test tube but not immersed in the BTB. Without full immersion in the BTB it affected the rate at which CO2 reached the BTB which has untold affects on the rate of color change. This failure throws off accuracy because it affects how much of the CO2 actually reached the BTB but also throws off precision because not everyone held the straw the same distance from the BTB and so the amount of CO2 to reach the BTB varies.
In order to improve the lab and prevent error while also remaining within time constraints the procedure should be modified with at least two changes. First a formal method for identifying when a color change has actually occurred should be introduced into the lab. This method would first exhibit a quick demonstration of the original color of BTB and then a sample run through of procedure until the BTB changes from a dark blue to a dark green so that everyone can observe what a change in color looks like. While the BTB may become a different color before its change to dark green, throwing off accuracy slightly, precision will be maintained minimizing error. Second, the straw length should be increased to a point where it will be allowed to immerse into the BTB fluid. This would allow whatever CO2 is produced by the user to sufficiently reach the BTB and would allow the rate of color change to be accurately gauged. Furthermore with the modification of straw length a formal method for breathing should be developed so that way the subject does not accidentally inhale BTB. This method would involve simple inhaling via the nose and then exhaling via the mouth.