Question

Based on the data of Respirstion of Peas at Room Temperature and Colder Temperature answer the following questions:

1. Write two hypothesis that this experiment is designed to test

2. Using the general gas law (V= nRT/p) 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.

3. Why does respirometer 3 serve as a negative control?

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

Background Many cellular processes require energy. Aerobic cellular respiration supplies energy by the oxidation of glucose. This is a complex process involving a number of enzyme-mediated reactions; however, we can berms of input and output products with a very simple equation: summarize the process in CcHyO+602-600 6H2O+energy Introduction You will use a respirometer to measure the rate of resptration of germinating and nongerminating pea seeds at two different temperatures. The respirometer consists of a vial that contains the peas and : volume of air. The mouth of the vial is sealed with a rubber 1-hole stopper that has a pipet inserted in it. The respirometer is submerged in water. If the peas are respiring, they will1 dioxide. Since 1 mole of carbon dioxide is released for each mole of oxygen consumed, there is change in the volume of gas in the respirometer. (Avogadro's Law: At constant temperature and pressure, 1 mole of any gas has the same volume as 1 mole of any other gas.) You will alter this equilibrium by placing a solution of potassium hydroxide (KOH) in the vial. Potassium hydroxide with carbon dioxide to form potassium carbonate, which is a solid. nese va cee s oxygen and release carbon use no reacts KCO3 +H20 CO2+2 KOH Since the carbon dioxide produced is removed by reaction with potassium hydroxide, as oxygen is used by cellular respiration the volume of gas in the respirometer will decrease. As the volume of gas decreases, water will move into the pipet. You will use this decrease of volume, as read from the scale printed on the pipet, as a measure of the rate of cellular respiration. Lon comma Measuring Respiration of Germinating and Nongerminating Peas Room-temperature water bath, cold water bath, codtainer of ice, paper (white or lined), water germinating peas, nongerminating peas, glass beads, respirometers, graduated tube, absorbent cotton balls, nonabsorbent cotton, 15% potasslum hydroxide (KOHD solution, dropping pipets, forceps, thermometers, stopwatch or timer or clock with second hand, calculators (optional). Materials Procedure Setup of Respirometers and Water Baths You will use two water baths (trays of water) to buffer the respirometers against temperature change and to provide two temperatures for testing rocm temperature and a colder temperature (approximately 10 C). Place a sheet of paper in the bottom of each water bath. This will make the graduated pipet easier to read. Next, place a thermometer in each tray. If necessars add ice to the cold-temperature tray to further cool the water to get it as close to 10°C as possible. While waiting for the cold-water temperature you should prepare an identicii set of three respirometers to test at the colder temperature. Preparing Peas and Glass Beads l h n You will need a set of peas and/or beads for testing at each temperature. Respirometer 1: Put 25 mL of H,O in your 50-mL graduated plastic tube. Drop in 25 germinating 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. Respirometer 2: Refill the graduated tube to 25 ml with H,O. Drop 25 dry, nongerminating peas fnto 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. Respirometer 3: Refill the graduated tube to 25 mL with of H,O. Add enough glass beads to volume of the germinating peas. Remove these beads and place them on a paper towel. equal the Respirometer Assembly You will need three respirometers for room-temperature testing and three respirometers for cold- temperature testing To assemble a respirometer, place an abscrbent cotton ball in the bottom of each respirometer vial. Use a dropping pipet to saturate the cotton with 2 mL of 15% KOH (Caution: Avoid skin contact with KOH Be certain that the respirometer vials are Place a small wad of dry, nonabsorbent cotton on top of the KOH-soaked absorbent cotton. The nonabsorbent cotton will prevent the KOH solution from contacting the peas. It is important that the amounts of cotton and KOH solution be the same for each respirometer dry on the inside. Do not get KOH on the sides of the respirometer.) Place 25 germinating peas in your respirometer vial(s) 1. Place 25 dry peas and beads in your respirometer vial (s) 2 Place beads only in your respirometer vial (s) 3. Insert a stopper fitted with a calibrated pipet into each respirometer vial. The stopper must fit tightly. If the respirometers leak during the experiment, you will have to start over Placement of Respirometers in Water Baths Place a set of respirometen1, 2, and 3) tn eachwebath with their pipet tips resting on one lip of the tray. See Rgure 1. Walt fire minutes before proceeding his is to allow time for the respirometers to reach themmal equilibrhm wieh the water. If any of the respirometers begins to fill with water, you have a leak and must start over Figure 1. Respirometers in the water bath. After the equillibration period, immerse all respirometers (including pipet tips) in the water bath. Position the respirometers so that vou can read the scales on the pipets. The paper should be under the pipets to make reading them eásiez Do not put anything else into the water bath or take anything out until all readings have been completed. Take Readings Allow the respirameters to equilibrate for another five minutes. Then, observe the initial volume readine on the scale to the nearest 0.01 mL Record the data in Table 1 for Time 0. Also, observe and Tecord the temperature. Repeat your observations and record them every five minutes for 20 mintes Table 1: Respiration of Peas at Room Temperature Respirometer 1 Germinating Peas Respirometer 2 Respirometer 3 Beads Only Dry Peas +Beads V of Pipet V of Corrected AV Corrected AV AV V of Time AV AV Pipet (Min) Pipet 10 .0% .05 20 S 12.04 20.8 05 35 .25 25 .04 5040 .05 .05 20. 10 .40 .13 05 691.51 3.75 20.8 .07 .59 ,05 .15 07 15 S0191 80 .05 V at time of current reading V at time o 20-20 73 AV= Corrected AV = AV (for Respirometer 1 or Respirometer 2)-AV of Respirometer 3 Table 2: Respiration of Peas at Colder Temperature Respirometer 3 Beads Only Respirometer 2 Dry Peas+Beads Respirometer 1 Germinating Peas Av Corrected AV V of Pipet AV Av Corrected AV V of Pipet V of Time °C (Min) Pipet 20 15 15 . 24-.0니 45 28 39 , 27 . ㅋ5|,55 5 .C5 37 41.26 ,% 5 82 10 4070 3 15 .o2,43 26 42 4 31 20 650 니01.25 34.19 90. at time O Respirometer 2)-AV of Respirometer 3 AV= V V at time of current reading Corrected AV=AV (for Respirometer 1 or

Answer 1

1. Hypothesis 1 - If both the germinating and non germinating peas are respiring, oxygen is consumed and carbon dioxide is released.

Hypothesis 2 - If carbon dioxide is released, it can be qualitatively estimated by reacting it with KOH.

2. Volume: It is constant initially according to Avogadros law. After a while when the CO2 reaccts with KOH, the volume of CO2 decreases in the vial.

n: No. moles of CO2 produced is equal to the moles of O2 consumed. When CO2 reacts with KOH, The number of moles of gaseous CO2 decreases in the vial.

Temperature: There is an increase in temperature during respiration as glucose in broken down.

Pressure: The pressure is constant initially but when CO2 formed reacts with KOH, the pressure inside the vial decreases.

3. It serves as a negative control, as no peas are used in the experiment. It is done to determine if presence of CO2 and the change in volume of the vial are independent of the process of respiration. If we see that there is lower pressure in control 3 as well as there is formation of Potassium carbonate. It nullifies our hypothesis about respiration.

4. According to the gas law, a change in the number of moles of CO2 (Decreases, as CO2 reacts with KOH) in the vial lead to a change (decrease) in the volume in the vial.
According to the gas law,
V (volume) is directly proportional to n (no of moles)