Lab 5 Cellular Respiration by Kris Layher


Lab 5 Cellular Respiration

Cellular respiration is the procedure of changing the chemical energy of organic molecules into a type that can be used by organisms. Glucose may be oxidized completely if an adequate amount of oxygen is present.

Equation For Cellular Respiration

C6H12O6 + 6O2 -> 6CO2 + 6H2O + energy

Carbon dioxide is formed as oxygen is used. The pressure due to C02 might cancel out any change due to the consumption of oxygen. To get rid of this problem, a chemical will be added that will selectively take out C02. Potassium hydroxide will chemically react with carbon dioxide by the following equation:

C02 + 2 KOH -> K2CO3+ H20

A respirometer is the system used to measure cellular respiration. Pressure changes in the respirometer are directly relative to a change in the amount of gas in the respirometer, as long as the volume and the temperature of the respirometer do not change. To judge the consumption of oxygen in two different respirometers you must reach equilibrium in both respirometers.

A number of physical laws relating to gases are important to the understanding of how the equipment that you will use in this exercise works. The laws are summarized in general gas law that states: PV = nRT Where:
P–the pressure of the gas
V–the volume of the gas
n–the number of molecules of gas
R–the gas constant
T= the temperature of the gas

In this experiment, the rate of cellular respiration in the germinating peas, in both water baths, will be much higher than that of the beads and non-germinating peas. The cooler temperatures in the other water bath should cause the rate to be much slower in all three respirometers.

A Water bath, thermometer, masking tape, washers, beads, germinating peas, non-germinating peas, beakers, graduated cylinder, ice, paper, and pencil are needed for this lab.

Begin the experiment by setting up two water baths, one at room temperature and the other at 10 degrees Celsius. Next, find the volume of germinating peas, non- germinating peas and bead, and beads alone. Repeat these steps for another set of peas and beads. Assemble the six respirometers, placing enough KOH pellets to cover the bottoms of the respirometers. Put non-absorbent cotton balls in each respirometer above the KOH pellets and then add the peas and beads.  Place one set of respirometers in the room temperature water bath and the other set into the 10 degree water bath. Slightly elevate the respirometers, supporting them with masking tape, for 5 minutes while they equilibrate. Then lower the respirometers into the water bath and take a  reading at 5, 10, 15, 20, 25, and 30 minute time intervals. Record the data into the table.

1. In this activity, you are investigating both the effect of germination versus non-germination and warm temperature versus cold temperature on
respiration rate. Germinating peas should consume more oxygen than non-germinating peas. Peas germinating at warm temperatures should consume more oxygen than peas germinating at cold temperatures.
2. This activity uses a number of controls. Identify at least three of the control, and describe the purpose of each control.
Water baths held at constant temperature
Volume of KOH is the equal in every tube
Equilibration time is identical for all respirometers

3. Graph the results from the corrected difference column for the germinating peas and dry peas at both room temperature and 10 degrees Celsius.

4. Describe and explain the relationship between the amount of oxygen consumed and time. The amount of oxygen consumed was greatest in germinating peas in warm water. The oxygen consumption increased over time in germinating peas.
5. Complete the following table:

6. Why is it necessary to correct the readings from the peas with the readings from the beads?
To show the actual rate at which cellular respiration occurs in the peas. The beads were the control variable.
7. Explain the effect of germination (versus non-germination) on peas seed respiration.
Germination, the seeds are growing and need to respirate to grow.
8.Explain the results shown in the sample graph in your lab manual. As the temperature increased, enzymes denatured so germination was inhibited.
9. What is the purpose of KOH in this experiment?
KOH pellets absorb carbon dioxide and form an insoluble precipitate
10. Why did the vial have to be completely sealed around the stopper?
The stopper at the top of the vial had to be completely sealed so that no gas could leak out of the vial and so that no water would be able to enter into the vial.
11. If you used the same experimental design to compare the rates of respiration of a 25 g reptile and a 25 g mammal, at 100 degrees Celsius, what results would you expect? Explain your reasoning.
I would expect the respiration to be higher in the mammal since they are warm blooded.
12. If respiration in a small mammal were studied at both room temperature 21 degrees Celsius and 10 degrees Celsius, what results would you predict? Explain your reasoning.
Respiration would be higher at 21 degrees because the animal would have to keep his body temperature up.
13. Explain why water moved into the respirometer pipettes.
While the peas underwent cellular respiration, they consumed oxygen and released carbon dioxide. The carbon dioxide reacted with the KOH resulting in a decrease in the volume of gas in the pipette and the vial. Because the pipette tip was exposed to the water bath, water moved into the pipette.
13. Design an experiment to examine the rates of cellular respiration in peas that have been germinating for 0, 24, 48 and 72 hours. What results would you expect? Why?
Set up four respirometers which have one of the following-Seeds that have not begun to germinate; Seeds that have been germinating for one day; Seeds that have been germinating for two days; Seeds that have been germinating for three days. It is expected that there will be no oxygen used by the seeds that have not germinated yet. The seeds that had been germinating for three days would consume the most oxygen.

Error Analysis:
The seals on the respirators may not have been completely air-tight. The use of KOH pellets, instead of liquid, may have caused errors in the carbon dioxide absorbed.  The temperature may have been slightly off in the water baths.

Oxygen consumption in the respirometers with germinating peas was greater than that in respirometers with non-germinating peas. Respiration rate was also affected by temperature. Respiration occurred at a faster rate in the respirometers in the warm water bath.