Cell Respiration

Introduction
To be able to carry on metabolic processes in the cell, cells need energy. The cells can obtain their energy in different ways but the most efficient way of harvesting stored food in the cell is through cellular respiration. Cellular respiration is a catabolic pathway, which breaks down large molecules to smaller molecules, produces an energy rich molecule known as ATP (Adenosine Triphosphate) and a waste product that is released as CO2. Basically, cellular respiration is a metabolic process that releases energy from organic compounds (such as C6H12O6) by metabolic chemical oxidation in the mitochondria within each cell. Proteins, carbohydrates, and fats can all be broken down into fuel for the cell but cellular respiration is usually correlated with glucose. Cellular respiration also requires O2 to carry out its pathway, as oxygen will act as a final electron acceptor. So, the final equation that can be represented for Cellular Respiration is: C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + heat. Cellular respiration is divided into three different stages.

Glycolysis, the first stage of cellular respiration, splits simple carbohydrates such as glucose into two molecules of ATP, two molecules of pyruvic acid, and two electron carried that have high energy that are known as NADH. This part of cellular respiration does not need oxygen, therefore ATP can be created by glycolysis, but it only makes a small amount and this method is not the most efficient method. The next stage in cellular respiration is the Citric Acid Cycle. This stage commences when the two pyruvate acids are converted into acetyl CoA. This pyruvate oxidation will produce 2 NADH and then the acetyl CoA will enter the Citric Acid Cycle. ATP is created during the Citric Acid Cycle will create 2 ATP molecules by substrate-level phosphorylation (which is made by enzymes) and molecules of NAD and FAD are reduced by electrons from the Acetyl CoA.

The Citric Acid Cycle is called a cycle because the original molecules used to start the process, Oxaloacetate (with 4 carbon), is created again at the end of the process. This process is also where the CO2 is made. The proceeding stage is the Electron Transport Chain. This chain requires oxygen, directly. This occurs in the membrane of the mitochondria. The electrons are passed to oxygen and creates a proton gradient is formed and ultimately ATP is made. An important mechanism of cellular respiration is that is can control it’s rate of it. This pathway can be shut off or slowed down when the products of the reaction. In the case of cellular respiration, the ratio of ATP to ADP/AMP will tell the cell whether to speed up the process or to slow down the process. Because of the allosteric enzyme phosphofructokinase is in glycolysis, depending on the ratio of ATP to ADP/AMP, the process will be inhibited or not and because it is in the beginning of cellular respiration, it will affect the whole system.

Cellular respiration can be measured in multiple manners; it can be measured in the consumption of O2, the production of CO2, and the release of heat or energy during the process. Questions that are asked during the lab is how the temperature of the water affects the rates of respiration of the peas and how the different peas will produce different amounts of oxygen and carbon dioxide. The hypothesis formulated during the lab was that only the germinating peas will consume the largest amount of oxygen and will convert the largest amount of CO2. Also, the temperature of the water will affect the rate of oxygen consumption in a direct proportion as in the higher the temperature, the higher the rate of consumption. The formula being used to measure the amount of the oxygen or carbon dioxide molecules is PV=NRT where P is the pressure of the gas, V is the volume of the gas, n is the number of molecules of the gas, R is the gas constant, and T is the temperature of the gas.

Methods & Materials
There are many procedures during this lab and many materials needed for an accurate analysis of data. First, fill a 100 mL graduated cylinder with 50 mL of water. Add 25 germinating peas and determine the amount of water that is displaced. Record this volume of the 25 germinating peas, then remove the peas and put those peas on a paper towel. They will be used for the first respirometer. Next, refill the graduated cylinder with 50 mL of water and add 25 non-germinating peas to it. Add glass beads to the graduated cylinder until the volume is the same to that of germinating peas. Remove the beads and peas and put on a paper towel. They will be used in respirometer 2. Now, the graduated cylinder was filled once again, determine how many glass beads will be require to reach the same volume of the germinating peas. Remove the beads and they will be used in respirometer 3. Then repeat the procedures used above to prepare a second set of germinating peas, dry peas and beads, and beads to be used in respirometers 4,5,and 6, the only difference is the temperature of the water. The respirometers will be prepared using two different types of cotton balls; nonabsorbent cotton and absorbing cotton. The absorbent cotton will be placed at the bottom of the respirometer and added with 15% KOH.

Then, the nonabsorbent cotton will be placed on top of the absorbent cotton. The procedure was done carefully so no KOH was added to the sides which would give misleading data. The first set of peas, which are the germinating peas, were added to respirometer 1. The second set of peas, the non-germinating peas and the beads was added to respirometer 2. The third set, the beads only, was added to respirometer 3. This process was repeated a second time for respirometers 4, 5, and 6. There is no difference in these respirometers, only that respirometers 4, 5 and 6 will be added to a warmer temperature. Two separate containers were filled with different temperature of waters. The cooler temperature was 10⁰C and the warmer was 25⁰ C. Tape was used to hold the respirometers up while dye was added into the tip in order to read the data. The data was recorded throughout 20 minutes, each at every 5 minutes.

Discussion & Conclusion
The hypothesis stated in the beginning of the report was correct. The higher the temperature, the more oxygen will be consumed. Also, the germinating peas consumed more oxygen than the dry peas and beads. There are many possible sources for the error. For example, there could possible human error by reading the data wrong or getting KOH on the sides which would give an inaccurate response. The equipment could be another source of error for the experiment

Graph the data for the respirometer 1 and 2 from your group’s tables. a) The independent variable is the time
b) The dependent variable is the oxygen consumed.

1) Write two hypotheses that this experiment is designed to test. One of the two hypotheses being tested in this activity could be some similar to how the warmer the temperature is the more respiration occurs. Another hypothesis that could be made is the germinated peas have a higher rate of respiration than non-germinated peas. These hypotheses could be tested with this lab.

2) Using the general gas law and your experience in this lab, 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 the influence of a variable(s). There are many different variables in this lab that could influence the outcome. The volume and pressure must be in ratio because they are correlated. Changing the temperature can change the experimental outcome, so the temperature during the experiment should be constant.

3) Which one of the respirometers serves as a negative control? Explain. The respirometer with only beads in it will be a control because it is the only group where no respiration will occur and because of that it can serve as a 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? Explain your answer. The two variables that are inversely correlated are pressure and volume. As pressure increases, the volume decreases and the other way around. A different variable that affects the change in volume is the temperature because they are directly proportional. The higher the temperature, the more change in volume will occur and the other way around.

5) Using your graph and data tables, summarize your findings, comparing results from respirometers 1 and 2, and results obtained at room temperature vs. results at the colder temperature. Speculate as to the causes of any differences between the treatments. At a higher temperature, there was more of a consumption of oxygen. This can be because there is more kinetic motion which will have more collisions that are necessary to break bonds that are needed to be broken in cellular respiration.

6) From your graph, calculate the rate of oxygen consumption for each:
a. germinating seeds at room temperature = 0.70 mL/min
b. germinating seeds at colder temperature = 0.20 mL/min
c. dry seeds at room temperature = 0.01 mL/min
d. dry seeds at colder temperature = -0.01 mL/min.