CHAPTER 8 Cellular Respiration Starting Points (Page 34) 1. (a) Organisms use the oxygen they absorb in cellular respiration to accept two electrons from the electron transport chain to produce water. (b) The carbon in carbon dioxide is from the carbon atoms found in the glucose molecule (C6H12O6). (c) Carbon dioxide is excreted by the body because it is fully oxidized and cannot provide any further energy. Carbon dioxide reacts with water to form carbonic acid. The buildup of carbonic acid may lower pH to toxic levels, which will denature proteins. 2. (a) Bakers add yeast to flour to produce carbon dioxide gas, which causes the baked product to rise. (b) The gas produced in fermentation is carbon dioxide. (c) The bubbling will stop when the glucose is used up. A high concentration of ethanol (a product of alcoholic fermentation) kills the remaining yeast cells. (d) Wine is produced. (e) The name of this process is alcoholic fermentation 3. (a) The reasons your muscles feel stiff after a long, hard run is because of the accumulation of lactic acid in the cells of your muscle tissues. (b) Panting at the end of a run increases your oxygen uptake and this helps your body to convert the lactic acid back into pyruvate. Exploration: Clothespins and Muscle Fatigue (Page 35) (a) (b) The strength of your squeezes should decrease with each successive trial. (c) Your hand and fingers will ache after the experiment. (d) Factors that may cause you to become less fatigued would be the size of the contracting muscles, adaptation to this type of activity, and the use of those muscles recently. (e) Your dominant hand should be able to contract more often than your nondominant hand. This reduction of fatigue is due to adaptation and increased strength of the muscles in your dominant hand. (f) After 10 minutes’ rest, you can repeat the same experiment with the same results because your body has removed metabolic wastes and replenished lost nutrients. 8.1 USABLE FORMS OF ENERGY Section 8.1 Questions (Page 41) 1. from lowest to highest energy: iv) glycogen, ii) maltose, i) glucose, iii) ATP, v) ADP. 2. In some reactions the formation of new products requires more energy than the breaking of the original bonds releases. This would result in the reaction needing energy to occur. In other reactions, the energy released during the breaking of reactant bonds is greater than the energy needed to form the bonds of the products. 3. Glucose has a high energy content, is relatively small, and is highly soluble. 4. Two processes that require the use of ATP are the movement of material up the concentration gradient (low to high concentration) and the movement of specific molecules through proteins in the cell membrane. Both of these processes require ATP in order to change the nature of the cell membrane or activate the membrane proteins. 5. Both animals use the waste energy (heat) to keep their bodies warm . Both organisms are warm blooded. 8.2 GLYCOLYSIS Section 8.2 Questions (Page 44) 1. Cellular respiration is required to convert stored food energy into the usable form of ATP. 2. Glycolysis, Pyruvate Oxidation, Kreb’s Cycle, and Oxidative Phosphorylation. 3. C6H12O6+ Æ 2 C3H6O3 (glucose) (pyruvate) 4. (a) Glycolysis refers to the breaking of the glucose molecule into two pyruvate molecules. (b) 2 pyruvate, 2 NADH, 2 ADP, 4 ATP 5. NADH and the 2 pyruvate molecules 8.3 AEROBIC RESPIRATION Investigation 8.1: Measuring Oxygen Consumption in Germinating Seeds (Pages 45, 65-66) Purpose To examine how oxygen consumption by dry and germinating pea seeds differs. Problem How does the rate of oxygen consumption by germinating and non-germinating pea seed vary? Hypothesis Since they are growing, germinating peas will have a higher need for energy and therefore a higher rate of cellular respiration than will non-germinating peas. Prediction (a) Students should predict that the germinating pea seed would consume more oxygen than the non-germinating pea seeds. Design The rate of production of CO2 gas will be measured in order to compare the respiration rate of germinating and non- germinating pea seeds. The seeds will be placed in a gas-tight sealed test-tube, along with potassium hydroxide. The potassium hydroxide will react any CO2 gas and form potassium carbonate (a solid) and liquid water. As a result, production of CO2 gas will cause a proportional decrease in the volume of gas in the sealed chamber. This will be detected by the movement of liquid in glass tubing. The manipulated variable the status of the pea seeds (germinating or non- germinating) and the responding variable is the rate of production of CO2. Controlled variables include the size of the test- tube and glass tube, the number of pea seeds, the number of KOH pellets, the time, and the temperature. Materials pea seeds (dry and pre-soaked) water paper towels nonabsorbent cotton laboratory scoop or forceps potassium hydroxide pellets (KOH) petroleum jelly liquid food colouring tape safety goggles laboratory apron 2 straight glass tubes 2 bent glass tubes 2 two-hole test-tube stoppers 2 large test tubes 2 millimetre rulers 2 pinch clamps 2 pieces of rubber tubing 2 test-tube clamps 2 retort stands medicine dropper Procedure 1. 30 dry pea seeds were placed in a large test tube and a layer of cotton was placed on top of the seeds. Using forceps or a scoop, approximately 30 KOH pellets were placed on top of the cotton. 2. A respirometer was assembled as shown in Figure 1. A millimetre ruler was attached to the end of the bent glass tubing, using tape. All stopper openings were sealed with petroleum jelly. 3. Steps 1 and 2 were repeated with 30 pre-soaked, germinating pea seeds. 4. Both respirometers were allowed to stand undisturbed for 5 min. 5. With the medicine dropper, a few drops of food colouring was added to the ends of the bent glass tubing. 6. A pinch clamp was added to the rubber tubing on each respirometer and closed. The time at which the pinch clamps were closed and the position of the food colouring were noted. 7. The movement of the food colouring in each respirometer was recorded every minute for 15 min. Evidence Students should include a table with the initial time at which the pinch clamp was closed, and then data at equal time-points (usually 1 min intervals) and the corresponding measurement of the food dye in the class tubing (distance from the open end of the tube). Data for both the germinating and non-germinating seeds may be included on one table or on two separate tables. (b) The food colouring will move toward the test tube. (c) The ruler is used to measure, indirectly, the rate of carbon dioxide production in terms of distance (mm). (d) The cotton is used to protect the seeds from the caustic KOH pellets. Analysis (g) The respirometer works by showing the consumption of air (oxygen) by monitoring the movement of food colouring. Respiration uses oxygen and produces carbon dioxide and water, the oxygen and carbon dioxide are gaseous. The carbon dioxide is removed by KOH so that it cannot influence the oxygen volumes in the apparatus. As oxygen gas is used, a partial vacuum is created in the test tube. External air pressure pushes the coloured water toward the test tube. By timing the movement of the coloured water, a relative rate of oxygen consumption can be established. (h) The openings are sealed to allow for only the oxygen inside the respirometer to be used to show the movement of food colouring and thus the use of oxygen. (i) Cellular respiration (j) The graph will vary with the data. It should be an upward diagonal straight line. (k) Sample calculation: Germinating Seeds Oxygen Consumption = total distance traveled / total time = 10 mm/10 min = 1 mL Nongerminating (Dry) Seeds Oxygen Consumption = total distance traveled / total time = 4 mm/10 min = 0.4 mL (l) The rate of oxygen consumption was much higher in the germinating pea seeds. Evaluation (m) The prediction is seen to be accurate. The rate of oxygen consumption in the germinating seed is 2.5 times that of the nongerminating seed. (n)The germinating seed will consume more oxygen than the nongerminating seed. This occurs because germinating seeds are growing and use more energy to do this. The energy comes from cellular respiration and oxygen is a reactant in the process. (o) If KOH had not been added, the level of air in the respirometer would have remained the same. As oxygen was used, carbon dioxide would have been produced and the food colouring would not have moved. (p) Photosynthesis. The peas are not photosynthesizing. Only leaves and to a certain degree stems are involved in photosynthesis. (q) The seeds themselves contain starch and other sugars that can be converted into glucose needed for cellular respiration. Synthesis (r) If seeds are too wet, there may not be enough oxygen to perform cellular respiration. In wet soil, there may not be enough dissolved oxygen and this will prevent cellular respiration from occurring and therefore the energy needed to grow will not be available. In addition, if seeds are too wet they may rot. (s) Begin by setting up a number of designs similar to that used in this experiment. Separate the seeds into a number of categories. Assign a minimum temperature to each group. Use a difference of 10 °C to separate the different groups. Keep each packet of seeds at the given temperature for 30 min.