Lab 6 Cellular Respiration Virtual Lab Worksheet (1) Doc

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Feb 20, 2024

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Name: _Nofisat Shoetan Cellular Respiration Virtual Lab Worksheet I. Watch this video to understand the cellular respiration lab set-up: Cellular Respiration Lab Walkthrough - YouTube Note: for your instructor’s convenience, please put your answers in blue or red . II. This virtual lab is based on a video that you can view here Or Watch here: Respiration and Respirometers - YouTube Watch this video at above link to conduct the lab and answer the questions. Cellular Respiration: C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O + ENERGY (ATP) 1. What are three ways that one can measure the rate of cellular respiration based on the above cellular respiration equation? a. The consumption of O2 b. Production of CO2 c. The release of energy during cellular respiration. 2. In this lab, we look at ___ the volume of O2 consumed. We do this volumetrically , using a respirometer Respirometer design # 1 :

Chamber with air, which contains respiring organisms (such as seeds). The tip of the tube is open, so water can enter. 3. Thought experiment: Assume that the seeds in the respirometer above are respiring. Complete the following sentences a) The O 2 content of air in the chamber would _decrease b) The CO 2 content of air in the chamber would increase c) What would happen to the volume of air inside the chamber and tube? _The volume of air inside the chamber and tube will stay the same. Respirometer design # 2 : To see how much O 2 is removed by respiration you have to remove the CO 2 that is produced by cellular respiration: We do this by modifying our set-up as follows: We soak the absorbent cotton with KOH (potassium hydroxide). KOH reacts with CO 2 as follows: 2KOH + CO 2 → K 2 CO 3 + H 2 O K 2 CO 3 (potassium carbonate) is a solid precipitate (not a gas) so it has very little volume. Liquid water also has very little volume. What we’ve done is soak up all the CO 2 produced by respiration. Make a prediction: What happens now? Complete the sentence below 4. As respiration proceeds the KOH soaked absorbent cotton will continue to react with the CO2 produced by the respiration and it will create K2C03 and water___ Watch Respiration and Respirometers . Stop at 1:56 (one minutes, 56 seconds) STILL ONE PROBLEM: In chemistry, you learned the formula PV=nRT (where P = pressure, V = volume, n = # of molecules of gas, R is the gas constant, and T is temperature)? Gas volume is affected by temperature, and temperature is one variable in this experiment.

For example, if we put our respirometer in cold water, what would happen to the volume of gas in the chamber? What would happen to our food coloring plug? 5. The volume in the gas would _decrease The position of the food coloring plug would move _down__ because the decrease in gas volume inside the chamber would create a negative pressure relative to surrounding water which would cause the flow into the chamber to try to equalize the pressure difference. WHAT CAN WE DO? Solution : Another respirometer w/ glass or plastic beads that we use to monitor pressure changes. Difference = (initial reading at time 0) – (reading at time X) Corrected difference = difference from respiration (column b) – difference from beads (column d) If we want to compare respiration in dry seeds and germinating seeds, we need to account for the fact that the volume of a single germinating seed (which has been soaked in water) will (because of osmosis) be much greater than the volume of a dry seed. If we want to do a one to one comparison, we need to equalize the number of oxygen molecules, and we do that by equalizing the volume by adding glass beads to the dry beads. Here’s what it looks like:

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Watch the video from 1:58 to 3:55 III. ANALYSIS QUESTIONS Answer the questions below. Make your answers as complete as possible. 6. What is the purpose to use the non-absorbent cotton in Respirometer design # 2 ? To protect the germinating seeds (respiring organism) from the KOH. 7. Do you think the dormant dry peas respire as much as the germinating peas? Why or why not? Dormant dry peas do not respire as much as germinating peas because they are not actively growing as germinating peas. Thus, they would respire less and much slower . 8. What is the purpose of KOH in this experiment? KOH removes carbon dioxide formed during respiration. 9. Why did the food coloring move toward the respirometer’s chamber? The food coloring moved towards the respirometer's chamber because as the organisms consume oxygen, the volume of gas inside the chamber decreases, creating a negative pressure relative to the surrounding water. Thus, the food coloring moving down the pipe indicates that oxygen is being consumed by the organisms inside the chamber . 10. Why was it necessary to correct the readings from the seeds with readings from the beads? The beads carried out no cellular respiration. The seeds did. Changes in atmospheric pressure could have caused changes in respiration rate and correcting the readings provided the most accurate results under the given conditions. 11. EXPLAIN the relationship between the amount of O 2 consumed and time . As time increased oxygen consumption increased . 12.Why is it important to have a control for an experiment? It is important to have control for an experiment to provide a basis for comparison with the experiment. Thus, it allows the experimenter to isolate the effect of the variable being tested. Without control, it would be complicated to determine whether any observed changes were due to the variable being tested or other factors.