Cool Cellular Respiration Lab

In this lab, we measured the effect of various conditions (temperature and germination) on the cellular respiration of mung beans and peas. Cellular respiration occurs in living things according to the following formula: C6H12O6 + O2 = CO2 + H2O. Therefore, because O2 is in the reactants and CO2 is in the products, a decrease of the former and an increase of the latter indicates that cellular respiration is occurring. On the other hand, photosynthesis occurs in autotrophs according to the following formula: Light + CO2 + H2O = O2 + C6H12O6, so a decrease in CO2 and an increase in O2 indicates that photosynthesis is occurring.

In order to observe the effects of these various conditions on cellular respiration, we came up with several groups of peas and mung beans and used Vernier lab probes to create graphs of O2 and CO2 concentration. The groups were glass beads (used as a control group because no cellular respiration or photosynthesis should occur), non-germinating peas at room temperature, non-germinating mung beans at room temperature, germinating peas at room temperature, germinating mung beans at room temperature, germinating peas in ice water, and germinating mung beans in ice water.

We started things off with a control group for the experiment. This was done by placing glass beads in the container with the Verniers. The results show that there is no cellular respiration or photosynthesis going on since they are not living objects. The graph shows this by the straight constant line across the graph. There is an increasing slope but that is due to the Verniers adjusting to the conditions of the container. Overall, no increase or decrease in CO2 and O2 levels. 

In the first portion of the experiment, we tested the CO2 and O2 concentrations for the peas and mung beans at room temperature. 

Here are the results for the peas, with CO2 levels indicated by the red line and O2 indicated by the blue line.

And here are the results for the mung beans with O2 indicated by the red line and CO2 levels indicated by the blue line.

For both the peas and mung beans at room temperature, the O2 levels decreased and the CO2 levels increased, which means that for these plants at room temperature, cellular respiration was occurring. At what rate preceisely? For the peas, the CO2 concentration increased at a rate of .583 ppm/sec and the O2 decreased at a rate of .0002167%/sec. And for the mung beans, the CO2 concentration increased at a rate of .183 ppm/sec and the O2 decreased at a rate of 0.0002667%/sec. This tells us that cellulalar respiration occurred at a slightly faster rate in the peas than in the mung beans, and this makes sens, for the peas were larger and therefore have a greater surface area on which their stoma can open and close to facilitate the movement of CO2 and O2.

We then tested to see of the change in temperature of the peas and beans affected the levels of carbon dioxide and oxygen. First we soaked 25 peas in 100 milliliters of 9 degree celcius ice water  for ten minutes. 

Peas in ice water bath

Then we put the peas in the Vernier apparatus.

After ten minutes had elapsed this was how our data looked.

We then conducted the same procedures for mung beans. 

First by soaking 25 of them in the 9 degree celcius ice water for 10 minutes. 

Then placing them in the Vernier apparatus to measure the carbon dioxide and oxygen levels in the tank as 10 minutes elapse. 

Below is our data:

The conclusion that we can draw is that the chilled beans and peas both went through less cellular respiration. We can infer this because from the data we gathered from the probes, compared to the non chilled beans and peas earlier in this lab, the rate of carbon dioxide being produced is less and the amount of oxygen being used up is less. Carbon dioxide being one of the products of cellular respiration and oxygen being one of the compounds used up in cellular respiration. This explains how locations with colder climates experience less vegetation. In the case of no sunlight, cellular respiration kicks in, but as we have discovered in this lab, cellular respiration does not work well when subjected to colder environments. 

In this part of the experiment we tested dried mung beans and peas to test and see what type of reaction would occur. What we did was take 25 peas and 25 beans and put them in a container with O2 and CO2 sensors. We left them in there for ten minutes and then recorded the data and evaluated the graphs. 

In this picture we have the mung beans in a sealed container with the sensors.

Data we collected: 

These are graphs of the data that the sensors recoreded at room temperature

From this data we can tell that for dried mung beans the overall trend of O2 was decreasing and the overall trend of CO2 was increasing. In cellular respiration Oxygen is being absorbed and carbon dioxide is being released. The mung bean graph follows that trend and therefore we can conclude that the mung beans were preformed get cellular respiration.

In the peas graph the overall trend for O2 is increasing and the overall trend for CO2 is decreasing. This means that carbon dioxide is being absorbed and oxygen is being released. This pattern follows photosynthesis because carbon dioxide is absorbed and oxygen is released when water is split in order to feed electrons into the cytochrome complex.

Cool Enzyme Lab

Part 2B:

In this part of the experiment we determined the baseline amount of H2O2 present in a 1.5% solution. We didn't add any enzymes to this reaction because this initial value that we will get is essentially the control group and so we need to know how much H2O2 was initially present in the solution.

First, we took about 10ml of 1.5% H2O2 and poured it into an empty cup. Then we added 1ml of H2O as a replacement for the enzymes. We need the solution to remain uncatalzyed so that our control value can be as accurate as possible, and so that is why we did not add the enzyme into the solution. After that, we took about 10ml of H2SO4 and poured it into the solution and mixed it all together.

In the picture above we are using a pipette to put 10ml of H2SO4 into the solution.

After we mixed the solution, we took a 5ml sample of it and we slowly added KMnO4, with a burette, to the solution until a pink color was obtained and stayed pink. The amount of KMnO4 used is directly proportional to the amount of H2O2 that was in the solution. When the solution turns pink that means the amount KMnO4 is exactly the amount of H2O2 in the solution because there is enough of each to react with each other.

In the photo above we are using the burette to slowly add drops of KMnO4 to the solution until it turns pink. Before we start to add the KMnO4 we take the initial reading of the burette and after the solution turns pink we take a final reading. If we subtract final-initial we get the total amount of KMnO4 used, thus getting the amount of H2O2 in the solution.

The figure above shows our final and initial readings of the burette. After our calculations we concluded that there was 3.5ml of KMnO4 present and therefore found the amount of H2O2 that was in the solution.

In conclusion, we found that 3.5 ml is our baseline value and that is the value that the rest of our trials will be compared to.

Part 2C:

In this procedure, we are determining the rate of spontaneous conversions of H2O2 to H2O and O2 in an uncatalyzed reaction. To find the data needed, we first needed to take 15mL of H2O2 and let it sit uncovered for 24 hours. Then we repeat the steps seems in 2B. We took 10mL of the H2O2 into a new beaker and added 1 mL of H2O (instead of the enzyme solution) and 10 mL of H2SO4. We mixed it well and then added the KMnO4 titration. Surprisingly enough, it only took less than five drops of the KMnO4 to make the solution pink. 

The image above shows the data collected. It only took .1 mL of KMnO4 to make the solution pink and 3.4 mL of the H2O2 was spontaneously decomposed; 97.14% was decomposed in 24 hours. What does this mean? By letting the solution settle overnight for 24 hours, the majority was decomposed naturally and only leaving a small amount left. This is why it took only a few drops of KMnO4. The less amount of H2O2 you have, the less amount of KMnO4 you need since both need to have equal quantities to keep the solution pink. 

Part 2D:

For this section, our goal was to observe the effect of time on the enzyme-catalyzed reaction that converts hydrogen peroxide into water and oxygen. We used the base line assay from Part 2B as a sort of control group. This showed us the original concentration of hydrogen peroxide in the solutions if the reaction were not permitted to occur. For the rest of the reactions we used the following method. We measured out 7 quantities of 10 mL of 1.5% hydrogen peroxide (the substrate for our enzyme), added 1 mL of catalase (an enzyme in yeast) to each quantity of hydrogen peroxide, and allowed the catalyzed reactions to persist for varying amounts of time (10, 30, 60, 90, 120, 180 and 360 seconds), after which we would stop the reactions by adding 10 mL of sulfuric acid. The acid reduced the pH of the solution, which denatured the enzymes by changing their shapes and behavior, which meant that they were no longer capable of catalyzing the reaction. For each solution, we performed a titration with potassium permanganate, wherein we slowly added the titrate to the solution until it remained pink or brown, at which point the volume of titrate equalled the volume of hydrogen peroxide present in the solution. Our results are in the table below...

The result, as we expected, was that the longer we permitted the reactions to be catalyzed, the less hydrogen peroxide would be left, as more of it would have been converted to water and oxygen. Here's the same information again in a graph of amount of hydrogen peroxide (substrate) used up in the reaction versus time. Note that it is not the amount of hydrogen peroxide left over but the amount that was used up...

In this graph, the data looks a little rough, but it gets the point across: the longer a catalyzed reaction is allowed to persist, the less substrate is left.

All in all, this lab gave us the chance to observe enzymes in action and understand their behavior in reactions. Understanding them in a lab environment like this gave us a better idea of how they function in the context of our bodies to regulate the rate of the reactions that sustain us.