Oxygen Consumption in Cellular Respiration

Introduction 

Dormant seeds are seeds that are living but have a seed coat around them. They have all the supplies they need to process and have a metabolism, and they would be able to germinate if they were under the right conditions.1 Germination occurs when dormant seeds are placed in the right conditions to start to enlarge and open so roots start to protrude. Oxygen, water, temperature, and amount of light are all important factors for germination. For peas to germinate, they need a dark, warm environment after soaking in water. 

Cellular respiration is a metabolic process. Eventually, catabolic reactions are used to break down an organic molecule to release energy. Cellular respiration occurs through three stages: Glycolysis, the Krebs Cycle, and oxidation phosphoralation. Cellular respiration is aerobic, and glucose (C6H12O6) and oxygen (O2) go into the reaction, and through the process, carbon dioxide (CO2), water (H2O), and up to 38 ATP are produced. This means that during the process, the glucose is broken down and the oxygen is consumed. As this happens, carbon dioxide and water come out and energy is released into the cell. 

The general gas equation, otherwise known as the Ideal Gas Law, states:

PV=nRT

such that P is pressure, V is gas volume, n is the amount of gas molecules, R is the gas constant that remains the same and is measured in units of the other aspects, and T is temperature of the gas. The general gas equation is important because it shows that pressure and volume are inversely proportional in the molecules and temperature stays the same. Also, if the molecule number stays the same, but the temperature changes, the pressure and volume are directly proportional to temperature and one or both will change in the same direction.

A respirometer measures how much oxygen is used during cellular respiration. The basic concept is, as oxygen from the air in the respirometer will be consumed in the reaction; the volume of the oxygen gas decreases, and the pressure decreases as well. When the pressure decreases, water from outside the respirometer will proportionally come into the pipette, and if the amount entering is measured, then the amount of oxygen consumed is the same.

Potassium hydroxide solution reacts with carbon dioxide to form potassium carbonate. The carbon dioxide will be completely used in the reaction, so none will be left in the surroundings. In the experiment, the carbon dioxide that is produced will move towards the 15% KOH solution and will create the solid potassium carbonate. Therefore, any volume change is not related to the CO2. 

The purpose of the experiment is to determine how much O2 is used in cellular respiration. In addition, the different rates of reactions of germinated peas compared to dry peas is tested to determine if one is more efficient, and different temperatures are tested to see which has the greatest effect.

It was hypothesized that the germinated peas will have a higher rate of reaction and therefore consumes more oxygen than the dry peas. Also, the peas in the warmer water will have a higher rate of reaction as well.

Materials and Methods

• 50mL tube
• H2O
• Tub with 10° C Water
• Extra ice
• Tub with room-temperature Water
• 50 germinating peas
• 50 dried peas
• Glass beads
• Paper towels
• Six vials
• Six stoppers with glass calibrated pipettes attached
• Absorbent cotton
• Nonabsorbent cotton
• Dropper
• 6mL 15% KOH solution
• 6 weights
• Tape
• Thermometer

The room temperature water tub was placed out before the experiment took place to insure that the water reached equilibrium. Ice was added to the water of the second tub to keep a constant temperature of 10° C. This temperature was maintained by adding ice when needed throughout the experiment.

A tube was filled with 25mL of H2O. 25 germinating peas were added, and the water displacement was recorded. This was the volume of the 25 germinating peas. The peas were then placed on a paper towel to dry off. The tube was refilled, and 25 dried peas were added. Glass beads were added until the same volume of germinating peas was reached. The peas and beads were placed on a paper towel to dry. The tube was refilled and only glass beads were added until the germinating peas’ volume was reached. The beads were placed on a paper towel to dry. The process of adding germinating peas, dried peas, and glass beads to 25mL of H2O was repeated so there were two sets of each.

Next, the respirometers were created. Absorbent cotton was placed on the bottom of each of the six vials. One milliliter of 15% KOH was placed on the cotton, making sure that the sides of the vials remained dry. Nonabsorbent cotton was placed on top of the moistened cotton. For vial 1, the first set of germinating peas was placed on top of the cotton. Vial 2 had the first set of dried peas and beads, and vial three had the first set of only beads. Vial four had the second set of germinating peas, vial five had the second set of dried peas and beads, and vial six and the second set of beads. The stoppers with the pipettes were placed in each vial. A weight was attached to the bottom of each.

Tape was placed across each tub to create a sling. The first 3 vials were placed in the tub of room-temperature water, and the last three were placed in the 10° C water tub. The pipettes of all were placed on the sling so that the vials were not completely in the water. After seven minutes, all the respirometers were submerged in the water so that the numbers on the pipette could still be read. After 3 minutes, the initial water amount was recorded for each vial. The temperature in both tubs was recorded. The water position was recorded for each vial in both tubs every 5 minutes for 20 minutes. Once done, the respirometers were taken apart, the cotton and peas were discarded, and the rest of the respirometers were washed and dried. The water in the tubs was discarded in the sink.

Results

It was hypothesized that the germinating peas would have a faster rate of reaction than the dried peas, and the ones in the room temperature water would have a better reaction rate than the ones in 10° water. The results support the hypothesis.

As shown in Table 3, the difference column shows the initial reading minus the reading of the time for each vial, this represents how much water has entered into the pipette since the beginning of the experiment. If the water entered more, then the pressure inside the vial must have decreased, therefore the oxygen in the vial must have been consumed during the experiment. The germinating peas had much more of a difference than the dried peas. Therefore, oxygen was consumed must faster in the germinating peas than the dried ones. The hypothesis was correct.

The glass beads were the control of the experiment, since there was no respiration taking place in those respirometers; therefore, if there were any outside forces affecting the experiment, they would be detected in this respirometer. In table 3, the difference in the initial and each time check was shown for beads. The pressure did change slightly in both the room temperature and 10° C water. This could be due to the temperature change of the air, resulting in the temperature change in the water and respirometer. According to the general gas law, if the temperature increases, the pressure or volume will also increase, and this would cause the water to leave the pipette. Therefore, the difference would be negative since there is less water in the tube than the initial amount.

The corrected differences shown in Table 3 are found by subtracting the difference of the bead’s initial reading and reading at the moment from the difference between the initial amount and the reading of the moment of the peas. This is the amount of pressure just lost only due to cellular respiration. When the corrected difference is negative, that means that the pressure increased in the vial, as discussed above. The corrected differences in the 20° water are shown in Figure 1. The germinating peas increased a lot more than the dried peas, shown by the steep slope of the germinating peas in 20° C water. The dried peas actually had a negative corrected difference, which indicates either an increase in pressure or increase in temperature. Figure 2 shows the corrected differences in the 10° C water. The germinating peas still had a higher rate of reaction for cellular respiration in the colder water. The dried peas had a negative corrected difference, so like the ones in the room temperature water, this indicates either temperature of pressure increases around the respirometers.

The hypothesis that cellular respiration would occur more in the room temperature respirometers than the 10° C water was correct. The germinating peas in the room temperature water consumed far more oxygen than the ones in the 10° water. As shown in Table 3, in the first five minutes, the germinating peas in the room water caused the pressure to drop .2 mL in the respirometer. The ones in the cold water only caused the pressure to drop .06mL, the big difference already shows that higher temperatures affect cellular respiration positively. Figure 3 shows the two germinating peas in the different water. The ones in room temperature water have a steep slope compared to the ones in the 10° C water. The curves indicate that the cellular respiration increased faster in the germinating peas in the room temperature water than the ones in the 10° C water. The difference between the two temperatures shows that the cellular respiration has an ideal temperature to achieve efficiency of the respiration, and that room temperature is better than 10° C water.