The purpose of this lab is to measure the consumption of oxygen by respiring seeds and to compare respiration rate at two different temperatures. Background Research: Cellular respiration is the process of oxidizing food molecules, like glucose, to carbon dioxide and water. C6H12O6 + 6O2 + 6H2O → 12H2O + 6 CO2
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.
an outer membrane that encloses the entire structure
an inner membrane that encloses a fluid-filled matrix
between the two is the inter membrane space
The inner membrane is elaborately folded with shelf-like cristae projecting into the matrix. a small number (some 5–10) circular molecules of DNA
“Cellular Respiration.” Cellular Respiration. N.p., 26 Nov. 2012. Web. 16 Jan. 2013. Gregory, Michael J. “Cellular Respiration.” Welcome to the Biology Lab. N.p., n.d. Web. 16 Jan. 2013. 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.
1.) Set up respirometers and water baths
2.) Respirometer 1: Put 25 mL of H2o in your 50 mL graduated plastic tube. Drop in 25 germinated peas. Determine the volume of water that is displaced (equivalent to the volume of peas). Record the volume of the 25 germinating peas. Remove these peas and place them on a paper towel.
3.) Respirometer 2: Refill the graduated tube to 25 mL with H2o. Drop 25 dry, nongerminating peas into the graduated cylinder. Next, add enough glass beads to equal the volume of the germinating peas. Remove the nongerminating peas and beads and place them on a paper towel.
4.) Respirometer 3: Refill the graduated tube to 25 mL with of H2o. Add enough glass beads to equal the volume of the germinating peas. Remove these beads and place them on a paper towel.
5.) To assemble a respirometer, place an absorbent cotton ball in the bottom of each respirometer vial. Use a dropping pipet to saturate the cotton with 2 mL of 15% KOH. Place a small wad of dry, nonabsorbent cotton on top of the KOH-soaked absorbent cotton.
6.) Place 20 germinating peas in your respirometer vial 1.
7.) Place 20 dry peas and beads in your respirometer vial 2.
8.) Place beads only in your respirometer vial 3.
9.) Insert a stopper fitted with a calibrated pipet into each respirometer vial. The stopper must fit tightly.
10.) Place a set of respirometer (1, 2, and 3) in each water bath with their pipet tips resting on one lip of the tray. Wait five minutes before proceeding.
11.) After the equilibration period, immerse all respirometers (including pipet tips) in the water bath. Position the respirometers so that you can read the scales on the pipets. The paper should be under the pipets to make reading them easier. Do not put anything else into the water baths or take anything out until all readings have been completed.
12.) Allow the respirometers to equilibrate for another five minutes. Then, observe the initial volume reading on the scale to the nearest 0.01 mL. Record the data in Table 1 for Time 0. Also, observe and record the temperature. Repeat your observations and record them every five minutes for 20 minutes.
To find the rate of oxygen consumption for each treatment, I divided each corrected volume by the time span of 5 minutes. Then added all and divided by the number of total entries (5). 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.
3.) Which of the respirometers (1, 2 or 3) serves as a negative control? Explain your answer. Respirometer 3, the respirometer with just the glass beads served as a control group that did not undergo cellular respiration. 4.) In the 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? Explain your answer. If temperature and pressure are kept constant, then the volume of the gas is directly proportional to the number of molecules of gas.
If the temperature and volume remain constant, then the pressure of the gas changes in direct proportion to the number of molecules of gas present. If the number of gas molecules and the temperature remain constant, then the pressure is inversely proportional to the volume. If the temperature changes and the number of gas molecules are kept constant, then either pressure or volume (or both) will change in direct proportion to the temperature. It is also important to remember that gases and fluids flow from regions of high pressure to regions of low pressure.
Beaker- Used to hold and heat liquids. Multipurpose and essential in the lab. Paper Towels- Paper Towels are essential to the lab environment. They will be used in almost every lab. Pipet- The pipet is used for moving small amounts of liquid from place to place. Stir Rod- The stir rods are used to stir things. They are usually made of glass. Stir Rods are very useful in the lab setting. Test tube Rack- The test tube rack is used to hold test tubes while reactions happen in them or while they are not needed.
Thermometer- The thermometer is used to take temperature of solids, liquids, and gases. They are usually in oC, but can also be in oF. Goggles- Protective eyewear that usually enclose or protect the area surrounding the eye in order to prevent particulates, water or chemicals from striking the eyes. Lab coat- necessary for many operations which could result in a large splash of harmful liquid, as well as for operations involving toxic solid materials that must be prevented from contaminating regular clothes, even in tiny quantities.