Lab Report: Measurement of Oxygen Consumption in Germinating Peas

Abstract

The purpose of this laboratory experiment is to measure the consumption of oxygen by respiring seeds and compare respiration rates at two different temperatures.

C6H12O6 + 6O2 + 6H2O → 12H2O + 6 CO2

Cellular respiration, the process of oxidizing glucose to produce ATP, was examined. The experiment involved setting up respirometers with germinating peas, dry peas, and glass beads while using potassium hydroxide (KOH) to absorb carbon dioxide. Oxygen consumption rates were determined by observing changes in volume over time.

The results revealed that germinating peas had higher oxygen consumption rates, and temperature affected respiration rates, with higher temperatures resulting in increased oxygen consumption.

Introduction

Cellular respiration is a vital metabolic process in which glucose is oxidized to produce adenosine triphosphate (ATP), the primary energy source for cells. It involves two major steps: glycolysis and aerobic respiration. Glycolysis occurs in the cytosol, while the remaining processes take place in mitochondria, where potential energy from food molecules is converted into ATP.

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The rate of cellular respiration can be influenced by factors such as temperature and the type of cells involved.

The energy in glucose is used to produce ATP. Cells use ATP to supply their energy needs. Cellular respiration is therefore a process in which the energy in glucose is transferred to ATP. The carbon atoms of the sugar molecule are released as carbon dioxide (CO2). The complete breakdown of glucose to carbon dioxide and water requires two major steps: 1) glycolysis and 2) aerobic respiration. Glycolysis produces two ATP. Thirty-four more ATP are produced by aerobic pathways if oxygen is present.

In eukaryotes, glycolysis occurs in the cytosol.

The remaining processes take place in mitochondria. Mitochondria are membrane-enclosed organelles distributed through the cytosol of most eukaryotic cells. Their number within the cell ranges from a few hundred to, in very active cells, thousands. Their main function is the conversion of the potential energy of food molecules into ATP.

Materials and Methods

The following materials were used in the experiment:

• Respirometers
• Germinating peas
• Dry peas
• Glass beads
• 50 mL graduated plastic tubes
• Water baths at two different temperatures (room temperature and 10°C)
• 15% potassium hydroxide (KOH) solution
• Absorbent cotton
• Dropping pipet

The experiment was conducted in the following steps:

1. Set up respirometers and water baths.
2. Prepare Respirometer 1: Fill a graduated tube with 25 mL of water and add 25 germinating peas. Record the volume of water displaced by the peas.
3. Prepare Respirometer 2: Refill a graduated tube with 25 mL of water, add 25 dry peas, and add glass beads to match the volume of the germinating peas. Remove the dry peas and beads, and place them on a paper towel.
4. Prepare Respirometer 3: Fill a graduated tube with 25 mL of water and add glass beads to match the volume of the germinating peas. Remove the beads and place them on a paper towel.
5. Assemble each respirometer by placing an absorbent cotton ball at the bottom and saturating it with 2 mL of 15% KOH. Add a small wad of dry, nonabsorbent cotton on top of the KOH-soaked cotton.
6. Place 20 germinating peas in Respirometer 1, 20 dry peas and beads in Respirometer 2, and beads only in Respirometer 3.
7. Insert stoppers fitted with calibrated pipets into each respirometer vial, ensuring a tight fit.
8. Place the respirometers in water baths with their pipet tips resting on the tray's lip, and wait for five minutes.
9. Immerse all respirometers in the water baths after the equilibration period.
10. Observe the initial volume reading on the pipets to the nearest 0.01 mL, record the data for Time 0, and note the temperature. Repeat observations every five minutes for 20 minutes.

Results

The results were obtained by measuring changes in the volume of gas in the respirometers over time. The rates of oxygen consumption for each treatment were calculated by dividing the corrected volume by the time span of 5 minutes. The data collected is presented in Table 1.

Table 1: Oxygen consumption data for different treatments at two temperatures.

Analysis

I have noticed that between tables one and two, the oxygen consumption at room temperature is higher. The germinated seeds at room temperature have a higher volume of pipet than the colder temperature. Same goes for dry peas and beads. The beads throughout the experiment did not change. It seems as if the peas at higher temperatures will have higher oxygen consumption. Between respirometers, the volume of pipet for both room and cold temperatures, have a farther distance from the initial volume (.01).

If the experimental design were to change by adding more KOH, it will cause more of it to precipitate at the bottom of the vial and no longer able to effect the readings. Also, if we were to not put glass beads in respirometer 2, the result might or might not change. Conclusion: The lab and the results gained from this lab demonstrated many important things relating to cellular respiration. It showed that the rates of cellular respiration are greater in germinating peas than in non-germinating peas. It also showed that temperature and respiration rates are directly proportional; as temperature increases, respiration rates increase as well. Because of this fact, the peas contained by the respirometers placed in the water at 10C carried on cellular respiration at a lower rate than the peas in respirometers placed in the room temperature water. The non-germinating peas consumed far less oxygen than the germinating peas.

This is because, though germinating and nongerminating peas are both alive, germinating peas require a larger amount of oxygen to be consumed so that the seed will continue to grow and survive. In the lab, CO2 made during cellular respiration was removed by the potassium hydroxide (KOH) and created potassium carbonate (K 2CO3). It was necessary that the carbon dioxide be removed so that the change in the volume of gas in the respirometer was directly proportional to the amount of oxygen that was consumed. In the experiment water will moved toward the region of lower pressure. During respiration, oxygen will be consumed and its volume will be reduced to a solid. The result was a decrease in gas volume within the tube, and a related decrease in pressure in the tube. The respirometer with just the glass beads served as a control, allowing changes in volume due to changes in atmospheric pressure and/or temperature.

In the lab setup used, the most viable part of the equation to measure would be the oxygen consumption because it would be the easiest to measure using a respirometer that removed. Gaseous carbon dioxide via precipitation (using KOH, K 2CO3 is a solid created when carbon dioxide and potassium hydroxide are combined). So, by quantitatively measuring how much O2 is consumed by a pea plant, the value can be inserted into the equation:

PV=nRT

Where P is Pressure, V is volume, n is the number of moles of gas, R is the Gas Constant (.08206atm L/ mol K) and T is Temperature in Kelvin. This formula is applicable as per Avogadro’s law, which determines that at constant temperature and pressure, 1 mole of gas is the same volume as1 mole of gas of another type. As the goal of the lab is to measure the rate in terms of mL/min, the pea’s use of oxygen pulls dye into the pipet and shows the change in volume. This change, divided by the time span of 5 minutes, provides the rate of oxygen consumption.

My hypothesis, if a pea is dormant, then the oxygen consumption will increase and vice versa. If a pea is at room temperature, then the oxygen consumption will be higher than the peas at 10 degrees Celsius, have been supported. Given the results from the data, the room temperature has higher oxygen consumption than the cold temperature. Respiration slowed down when the temperature was reduced, and respiration increased when the temperature increased. The germinating pea seeds consumed the most oxygen. The vials containing the dry seeds and glass beads had the same result. When the germinating seed is cooled down however, the rate of oxygen consumption is reduced drastically because all of the cellular processes are slowed down from the cooler surroundings. The germinating seeds consumed almost no oxygen throughout the experiment in the 10-degree C water bath.

In the room temperature water bath, the glass beads, and the dry pea seeds and glass beads consumed the least amount of oxygen. This means that the germinating seeds would slow down their respiration rates because of the colder temperature. There may be errors during the experiment. 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. I have learned the understanding of relationships between temperature, pressure and volume, study the effects of diffusion through a semipermeable membrane, and quantify oxygen consumption rates in germinating peas under different conditions.

Conclusion

This laboratory experiment successfully demonstrated the differences in oxygen consumption rates between germinating and non-germinating peas and the effect of temperature on respiration rates. Germinating peas exhibited higher oxygen consumption due to their increased metabolic activity, while higher temperatures accelerated respiration rates.

The use of respirometers and the removal of carbon dioxide with KOH allowed for accurate measurements of oxygen consumption. The experiment provided practical insights into cellular respiration and its regulation under different conditions.

Recommendations

For future experiments or investigations related to cellular respiration, it is recommended to consider the following:

1. Ensure airtight seals on respirometers to prevent any leaks that could affect measurements.
2. Consider using liquid KOH instead of pellets to absorb carbon dioxide for more precise results.
3. Maintain precise control over temperature in water baths to accurately assess temperature's impact on respiration rates.
4. Explore additional factors, such as varying glucose concentrations or pH levels, to further investigate their influence on cellular respiration.