David Huang!
AP Biology!
November 29, 2013!
Rate of Cellular Respiration:!
Germinated vs. Non-Germinated!
10°C vs. Room Temperature!
Introduction:!
!
The main focus of the lab was to measure and record the respiration of peas, both
germinated and non-germinated, and the effect of temperature on the peas. Cellular respiration is
the process in which cells consume oxygen and glucose to produce energy along with the by
products of carbon dioxide and water. In this experiment we will measure the rate of cellular
respiration among the peas by looking at the decrease in volume of the respirometer. Though in
cellular respiration, there will be a release of carbon dioxide it will be eliminated with the use of
potassium hydroxide (KOH). The chemical equation of the process can be modelled as: CO2 + 2
KOH —> K2CO3 + H2O. The resulting product of the reaction is a solid which will not decrease or
increase the volume in the respirometer. With oxygen levels decreasing in the respirometer there
will consequently be a decrease in the overall volume thus drawing the water through the pipet.
Therefore, the further the water is drawn into the pipet, the more the cells are respiring as they are
using up the oxygen. !
!
Materials: !
-
!
Room-temperature water bath
Container of ice
Water
Non- germinating peas
Respirometers
Absorbent cotton balls
15% potassium hydroxide (KOH) solution
Forceps
Stopwatch or timer!
- Cold water bath (starting at 10°C)!
- Paper!
- Germinating peas!
- Glass beads!
- Graduated tube!
- Non-absorbent cotton!
- Dropping pipets!
- Thermometers!
Procedure:!
!
The 10°C temperature water bath can be obtained by putting ice into a room temperature
water bath until the temperature is achieved. When both water baths have reached the desired
temperatures, a sheet of paper must be placed into the bath for easier reading of the pipets. Three
respirometers will be needed for each of the water baths. The respirometers can be assembled by
placing an absorbent cotton ball at the bottom of each respirometer vial. The cotton balls will then
be saturated with 2ml of potassium hydroxide (KOH). After having done so, non-absorbent cotton
must be applied onto the absorbent cotton as to prevent any contamination. 25 germinating peas,
25 dry peas and beads**, and beads will then be added to each of the three respirometers
measured as vial 1, 2, and 3, respectively. With the contents inside the vials, the stopper, with a
pipet inserted into it, can then be fitted onto the respirometer vial. !
!
Before the pipets can be submerged into the water baths, they must have a period to reach
equilibrium. To do this, the pipets must be partially submerged in the water baths with the tip of the
pipet out of the water. After five minutes of this, the pipets can then be submerged. Recordings of
the pipets can then be taken every 5 minutes up to 20 minutes. Be sure not to touch the pipets or
the water bath in general as this can disturb the pressure of the vials causing falsified data. !
!
** To determine the number of glass beads needed to be added to the dry peas and respirometer 3
,the volume of the 25 germinated peas must first be determined (this can be done so by adding the
peas into a graduated cylinder of water and calculate the volume displaced, the result will be the
volume of the germinated peas). !
!
!
Tables: !
Table 1-1 (above), Shows the volume of the pipets at the given times when submerged in a room
temperature water bath. The V change in volume and the corrected delta V is = delta V - delta V of
respirometer 3. !
Table 1-2 (above), Shows the volume of the pipets at the given times when submerged in a colder
temperature water bath.!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
Analysis of Results:!
1. Write two hypotheses that this experiment is designed to test.!
1. If the temperature is maintained at room temperature, the rate of cellular respiration will be
greater than that of the cooler temperature.!
2. If the peas are germinated before the experiement, the rate of cellular respiration will be
greater than the other two (i.e. peas and beads, and beads only).
2. In this experiment, you measured the change in volume of the gas inside the respirometers. The
general gas law describes the state of a gas under given conditions. !
!
pV = nRT!
Using the general gas law and your experience in this lab, give the variables that had to be
controlled for your data to be valid. State the controls used for each variable and any means used
to correct for the influence of a variable(s). !
!
For the data to be valid the time given for the pipets, in both the cold and room temperature
bath, had to be the same which was around five minutes, the intervals that the data was recorded
must also be constant which were 5 minute intervals until 20 minutes, the starting volume of the
respirometers had to be the same (all of the volumes were equal to that of the germinated peas
volume), the amount of potassium hydroxide (KOH) dripped onto the cotton was also kept constant
for each of the respirometers. To deal with the carbon dioxide emissions, KOH was added to cotton
pads so that it could convert the carbon dioxide into a solid state (K2CO3). !
!
3. Which of the respirometers (1, 2, or 3) serves as a negative control? Explain your answer.!
!
Respirometer 3, the one filled with only the glass beads, served as the negative control of
the experiment. In this respirometer, there could have been no factor that could cause the oxygen
capacity or volume to change in the respirometer; thus, it allowed us to confirm that the
preparations of the respirometers were correct and that there were no other factors that could
affect the experiment in an unforeseen way since there were glass beads added to the nongerminated peas vial. !
!
4. In reference to the general gas law, and assuming your control measures worked, a change to
which of the variables led to the observed change in volume (Corrected delta V in Tables 1 and 2)?
Explain your answer. !
!
The change in volume, or rather the decrease of it, was caused by the respiring of the
peas. When the peas undergo cellular respiration it releases carbon dioxide and consumes
oxygen. However, in this experiment the carbon dioxide is converted to a solid via the potassium
hydroxide; thus, there’s only a decrease in oxygen which leads to the overall decrease of volume in
the respirometers. !
!
5. Using your graph and data tables, summarise your findings, comparing results from
respirometers 1 and 2, and results obtained at room temperature vs. results at colder temperature.
Speculate as to the cause(s) of any differences between the treatments.!
!
Respirometer 1, which contained germinated peas, had a higher respiration rate in both the
warmer (room temperature) and the colder temperature when compared to respirometer 2. The
reason for this is because germinated peas are growing while the dry peas are inactive and
therefore do not undergo cellular respiration as rapidly. When comparing the results of the cooler
temperature bath and the warmer temperature bath, it was found out that peas respire more in
cooler temperature— mind you this is an anomaly and ultimately a mistake in the data or the
procedures. In theory, the peas should have respired more at room temperature because the peas’
enzymes that aid in the process of cellular respiration is the most productive at room temperatures
rather than 10°C. !
!
!
!
!
!
!
!
Conclusion:!
!
The data that was obtained was quite different than what was expected mostly because the
data was incorrect. For example, it is highly unlikely that the glass beads will consumed oxygen.
Our data, however, showed that it did. This is most likely caused from human error. When reading
the pipet for the volumes, one of the group members had touched the pipet which could have
caused water to flow into the pipet due to pressure change. Another error that needs to be
addressed is the increase in volume for respirometer 2 that was submerged in the cold bath
between 15 minutes to 20 minutes (this can be seen from the graph). Perhaps this was also
caused from human error. A strange observation was that the peas respired more rapidly at cooler
temperatures than at warmer temperatures which is not supposed to happen. To address these
issues for experiments in the future we must make sure whoever is taking the readings for the
pipets must not touch them. Furthermore, we will include more test groups as to see if the peas
really do respire at cooler temperatures. Aside from all these flaws in the experiment, it was true
that the germinated peas did respire more rapidly that the non-germinated peas. To this end, there
will need to be improvements in the procedures of the experiment next time as to assure a more
accurate data set. !