Exercise 11: Respiration
In this exercise you will be learning more about the process of aerobic respiration. This metabolic process is central to the metabolism of plants and animals. As you saw in the pre-lab exercise, changes in these metabolic processes in humans can have a significant health impact. Although it would be ideal to be able to learn about the respiration process in humans, it is not practical from an experimental perspective.
We therefore will look at other organisms as our models for understanding the respiration process. In our case, we will use both a plant and an animal model; garden peas and mealworms will be used as the experimental organisms. In the first part of the experiment, you will be using garden peas to answer two questions about respiration. You will be watch two videos that examine carbon dioxide and oxygen and their role in respiration. You will propose a hypothesis that would answer your question and then watch a video that will show you the results of your measurements.
Aerobic cellular respiration (also known as glucose oxidation) is the process by which energy stored in the chemical bonds of molecules like glucose is harvested and transferred into ATP (adenosine triphosphate). The energy in ATP can then be used to power the metabolism of the cell. All living organisms use ATP to power their metabolism.
The overall reaction for the process is
C6H12O6 + 6O2 + ADP + Pi → 6CO2 + 6H2O + ATP
This overall reaction greatly simplifies the overall process, showing only the first reactants and the final products of respiration. The overall process is a sequence of reactions that are divided into three stages. Glycolysis, which occurs in the cytoplasm of the cell, takes a glucose molecule and splits it into two parts. The second stage, the Krebs cycle, takes these the two molecules that are the end products of glycolysis and dismantles them further, releasing energy from the chemical bonds that are successively broken. In the third stage, the electron transport chain phosphorylates ADP to ATP in a process known as oxidative phosphorylation. Both the Krebs cycle and oxidative phosphorylation occur in the mitochondria of eukaryotic cells.
Activity 1: Respiration in Garden Peas
What is the question we would like to answer?
It is well known that pea plants carry out the process of cellular respiration. But what about the pea (the seed at the start of the germination process? Obviously, the seed must be alive, or it wouldn’t be able to germinate and produce a new plant. So does that mean that the pea itself is also performing respiration early in germination even before there are leaves present on the plant?
Do peas perform cellular respiration during germination?
How do we answer the question from a scientific standpoint?
Develop a hypothesis
Based on the information you have read previously, you should now know that the way that scientists answer a question is to develop a hypothesis that is a tentative answer to the question. Remember, it does not matter whether your hypothesis is “right or wrong,” only that it can be tested experimentally.
Now, you should develop a hypothesis that might answer the question posed at the beginning of this section; do peas undergo cellular respiration during germination? It does not matter if your hypothesis is correct or not in the end, just that the hypothesis can be tested. In either case, whether you accept or reject your hypothesis, if done correctly, you should have learned something.
Question 1-1: Now, write your hypothesis for answering the question “do peas undergo cellular respiration during germination?” on the Skill Check work sheet for this experiment.
Make a prediction
When you start to think about how you would test your hypothesis, you will need to think about how you would interpret the data that will be generated from your experiment. It is important that you decide what the results might mean in advance of doing the experiment. For example, we know that carbon dioxide (CO2) is produced as an end-product of the reactions that occur in respiration and that oxygen (O2) is used by the organism during the same reactions. Remember that you should have a control for what you are doing.
Question 1-2: Write a prediction on your answer sheet that addresses what you would predict will happen to CO2 levels in the vicinity of the organism if it is performing or not performing respiration. Remember, predictions tend to be posed as if/then statements.
As it turns out, there is equipment available that can measure amounts of CO2. There are, however, some limitations to this equipment. Since the amounts of CO2 that would be produced would be very small compared to the volume of air surrounding us, it would be best if we could keep this CO2 in a confined space where changes could be measured more easily. The first video that you will watch will have a lab-built system that will allow you to determine whether or not two different sets of peas are able to produce CO2..
Now watch the video at the following website. Take careful notes on what you see as they review the data near the end of the video and fill in the data in Table 1 of the Skill Check Worksheet.
Now, answer the following questions on the Skill Check Worksheet.
Why did one of the pea cultures appear to produce CO2 while the other did not?
From a biochemical standpoint, what does boiling do to the peas?
What conclusions can you draw based on the data that was generated?
Activity 2: Oxygen and Carbon Dioxide in Respiration
What if you had a piece of equipment available that would allow you to measure amounts of CO2 or O2 in the air? What might you predict would happen to the levels of these gases in the vicinity of the organism if the organism was performing respiration?
In this experiment, two sensors will be used, one that is capable of measuring the amount of CO2 gas that is present in a closed system (i.e. a bottle containing the organisms in question, that is sealed and does not let air or CO2 to either enter or escape. It turns out that we can use the sensor that can measure the CO2 gas to act as the “cork” for the bottle. The sensor is attached to an input box that connects to a computer that will collect data and help you to analyze it. The apparatus, when set up, will look similar to this except that there will be two probes inserted into the respiration chamber instead of just one.
Organisms inside Respiration Chamber
Organisms inside Respiration Chamber
The second sensor will be used in the side of the same respiration chamber that is capable of measuring the amount of oxygen in the chamber.
Watch the video at https://www.youtube.com/watch?v=cWJdDB73jvU&feature=youtu.be
Question 2-1: What did you see happening to the CO2 level in the chamber? Did this surprise you or not?
Question 2-2: What happened to the oxygen level in the chamber? Explain this result in terms of the process of cellular respiration.
1. Do you have any evidence that cellular respiration occurs in peas? Explain.
2. What is the effect of germination on the rate of cellular respiration in peas?
3. Which of the tests was your control for this series of experiments? What did you learn from that control?
4. Summarize what you learned about cellular respiration