December 8, 2011
AP Biology Lab 5: Cellular Respiration
In this lab we are testing how the process of cellular respiration is affected by temperature, and also how it is different between germinating and non-germinating peas. Cellular respiration is a catabolic process (breaks down organic material into usable cell energy) that produces ATP. The electron receivers are inorganic. Cellular respiration releases energy from organic material through chemical oxidation within the mitochondria of cells. Cellular respiration usually refers to the metabolizing of glucose, however carbohydrates, proteins and fats can also be metabolized. C6H12O6 + 6O2 → 6CO2 + 6H2O + 686 Kcal of energy/mole of glucose oxidized Cellular respiration can be measured by looking at the consumption of O2, the production of CO2, and the release of energy. PV=nRT is known as the inert gas law where: P is the pressure of the gas, V is the volume of the gas, n is the number of molecules of gas, R is the gas constant, and T is the temperature of the gas in degrees Kelvins. This law is very important and we can infer many things when given some parts of the equation, for example: “if the number of gas molecules and the temperature remain constant, then the pressure is inversely proportional to the volume”, that is just one of the direct proportions. Also in this lab, potassium hydroxide (KOH) can be used to remove the CO2 produced during cellular respiration, therefore the change in volume in gas we see in our respirometer will be directly related to the amount of oxygen consumed by the peas. The reaction is: CO2 + 2KOH → K2CO3 + H2O Materials:
20 germinating peas, 20 dry peas, 225 glass beads (approx.), 6 mL 15% potassium hydroxide, 2 water baths, 6 respirometers, 6 absorbent cotton balls, 6 nonabsorbent cotton balls, 50-100 mL graduated cylinder, thermometer, pipet, stopwatch, ice, food coloring, paper towels Methods:
The first thing we did for this lab was set up 2 water bath/trays, one with water at room temperature and the other we kept at a constant 10 degrees Celsius by adding ice into the tray. We were also provided with 6 vials with steel washers, in which we labeled them 1-6. We then filled a graduated cylinder to 13 mL water ( we kept it constant throughout the lab .) First we added 10 germinating peas into the graduated cylinder and then took a reading of the displaced water. We recorded this data, decanted the water, and placed the peas to dry on a paper towel. We repeated this process, but instead we added 10 non-germinating peas also with glass beads until the water level was the same as the germinating peas, and then placed them to dry on a paper towel. Next we repeated the process, but we added only glass beads until the water level was same as the germinating peas. We repeated the same steps respectively and set the second set of peas and beads aside for use in vials 4-6. For the next part of the lab we placed an absorbent cotton ball into each of the 6 vials and pushed each to the bottom of the vials. We then carefully added 1 mL of provided 15% potassium hydroxide (using pipets) to each of the cotton balls, after that we placed a piece of non-absorbent rayon on top of the KOH soaked cotton. With the first set of germinating peas, non-germinating peas, and glass beads we added them into vials 1-3 respectively. We added the second set of peas and glass beads into vials 4-6. We had graduated pipets with stoppers at the end provided. We then placed each stopper into each of the vials, creating a seal; and we then placed a washer over the pipet on top of the stopper (so that the vials are weighed down in the water baths later.) After that we placed vials 1-3 into the room temperature water bath, with the pipet ends resting on the edge of the water tray, and placed vials 4-6 into the chilled water bath and allowed the vials (respirometers) to equilibrate for 10 minutes. After that we put one drop of...