Respiration of Yeast Respiration and How Carbon Dioxide is Produced Aerobic respiration includes glycolysis, the Link Reaction, the Krebs Cycle and oxidative phosphorylation. It is the process by which glucose is broken down multiple times while NAD and FAD are reduced. These hydrogen ions drive the production of ATP from ATP synthase after chemiosmosis. However, carbon dioxide is only produced in the Link reaction, as Pyruvate converts to Acetate, and in the Krebs Cycle twice. For one molecule of glucose, 6 molecules of carbon dioxide are produced and 32 molecules of ATP. The Structure of Carbohydrates Carbohydrates are usually polymers made up of monomers (monosaccharides). A hexose monosaccharide has 6 carbons and can be Alpha, if the H is above the OH on Carbon 1, or Beta, if it is below. All carbohydrates are made up of carbon, hydrogen and oxygen, with the formula: CnH2nOn. Monosaccharides can join together by glycosidic bonds to form disaccharides. A condensation reaction occurs, removing a molecule of water. A polysaccharide is more than two monomers joined together. Equipment Yeast Suspension 5 x Sugar Solutions (Glucose, Sucrose, Lactose, Maltose & Fructose) 5 x Boiling Tubes Water bath (at 25°C) 6 x Pipette Boiling Tube Rack 6 x 10cm3 Measuring Cylinders Gas Syringe (with Boiling Tube Bung & Delivery Tube) Timer/Stopwatch Method 1. 2. Collect equipment and set up as shown in diagram below. (2) Use clean pipette to add 5cm3 of sugar solution, of known concentration, to a clean measuring cylinder. (1) (2) 3. Add 5cm3 of sugar solution to all 5 boiling tubes in water bath. (1) (2) 4. Leave for 5 minutes for sugar solution to come to temperature. (1) 5. Use pipette to add 5cm3 of yeast suspension to clean measuring cylinder. (2) 6. Check gas syringe is set to 0, then add yeast suspension to one boiling tube, immediately add bung and start timer. (1) 7. After 5 minutes record the volume of CO2 produced in results table, then remove bung. (1) 8. Repeat steps 5-7 for remaining 4 boiling tubes to calculate average. (1) 9. After completing 5 tests on one sugar solution remove all boiling tubes and rinse out. 10. Place boiling tubes back in rack and repeat steps 2-9 for all sugar solutions. Results Table Carbohydrate Volume of carbon dioxide produced after 5 minutes (cm3) Test 1 10 5 6 4 8 Glucose Sucrose Lactose Maltose Fructose Test 2 12 5 5 3 7 Test 3 12 4 4 3 6 Test 4 11 3 6 4 7 Test 5 9 4 5 3 8 Rate of CO2 Production (cm3/min) Average 10.8 2.16 4.2 0.84 5.2 1.04 3.4 0.68 7.2 1.44 Graph A graph showing the rate of carbon dioxide production per minute by yeast respiring 5 different carbohydrates 2.50 Rate of carbondioxide production(cm3/minute) 2.00 1.50 1.00 0.50 0.00 Glucose Sucrose Lactose Maltose Fructose Carbohydrate respired Conclusion As the graph shows, glucose was respired fastest with an average of 2.16cm3 of carbon dioxide produced per minute and fructose was the second fastest at 1.44cm3/min. Glucose immediately entered glycolysis and went on to produce carbon dioxide, whereas fructose had to be altered before it could enter glycolysis due to its different structure. Fructose was 0.72cm3/min slower than glucose due to the time taken to alter its structure which slowed the respiration rate. Sucrose, Lactose and Maltose were respired the slowest because they are all disaccharides, meaning they contain a glycosidic bond. This bond prevented them from entering glycolysis immediately. The enzymes sucrose, lactase and maltase were needed to break these bonds by hydrolysis but first had to be synthesised at ribosomes. This led to the yeast cell being slow at respiring these carbohydrates as protein synthesis took time and therefore the yeast produced less carbon dioxide over 5 minutes, the lowest being Maltose at 0.68cm3/min.