Shivaan Mohinani November 10th 2018 Pag 12.1 Investigation into the respiration rate of Saccharomyces cerevisiae Introduction: Respiration is the process in which organic molecules (e.g. glucose) are digested and broken down into smaller inorganic ions such as carbon and water, and the energy is stored within bonds.1 Aim: We want to test the effects of different substrates glucose, fructose, sucrose and lactose) on the respiration of yeast. The way in which I will do this is by measuring the amount of CO2 released from anaerobic respiration using a gas syringe. Key Info: As yeast are not capable of the process of creating their own food, they require foods (e.g. sugar) to survive, and they accomplish this through absorption of specific nutrients by the secretion of extracellular enzymes – known as saprotrophic nutrition.2 The higher the concentration of the enzye substrate the faster the rate of the breakdown and therefore CO2 is produced. Also due to higher substrate, there are more molecules to occupy the active site therefore a faster reaction. If the enzyme eventually forms then more CO2 will be produced, however this only happens for a short period until all active sites are saturated with substrates. As we know, yeast can also respire anaerobically and aerobically depending on O2 levels therefore depending on the levels inside the test tube. As both fructose and glucose are both monosaccharides, we can assume that they will not need an enzyme to break them down, therefore meaning they will produce the most CO2 a they will react the quickest. 3 Hypothesis: Null Hypothesis: With different substrates, the amount of CO2 produced with yeast will also change Alternative hypothesis: With diff. substrates the amount of CO2 produced will be the same Method: 1. Make a water bath at a temperature of 40C and ensure all apparatus is sterile and clean 2. Weigh 10g of yeast using the weighing scale and add it to a beaker 3. Using a pipette, measure 40ml of water and add it to the yeast and stir until well mixed. Make sure you leave it long enough before starting experiment. 4. Using a pippete, measure out 10ml of each of our substrate solutions (Glucose, fructose, sucrose, lactose) and put them each in their own sperate boiling tubes (using a market to label each one) 1 OCR A Level Biology textbook by Ann Fullick: page 123 OCR A Level Biology textbook by Ann Fullick: page 351 3 https://www.scientificamerican.com/article/exploring-enzymes/ 2 Shivaan Mohinani November 10th 2018 5. Next place the 4 in the 40 degrees Celsius water bath 6. Set up the beehive by putting it in a basin of water in which the beehive is below the surface, and fill a measuring cylinder with water below the surface and ensure you can place it on top (noting the starting volume of the cylinder). Pass a rubber tube from the bottom of the beehive into a bung 7. Next, using a pippete, measure 10ml of yeast solution and place it in the substrate test tube (after being left in the water bath to acclimatize) 8. Immediately cover the test tube with a bung (leaving it in the water bath) 9. When the first bubble emerges from the beehive and into the measuring cylinder, start the stop watch 10. After this, every single minute, for 5 minutes, note how much the water level in the measuring cylinder has decreased 11. Repeat steps 7-11 for the remaining other 3 substrates Apparatus: Bee hive Water bath – heated to 40C Dry Yeast Boiling tubes Distilled water Substrates (glucose, fructose, sucrose, lactose) Electronic weighing scale Stop watch Rubber bung Rubber tube Pipette (15cm3) Measuring cylinders Stirring rod Beakers Results: Shivaan Mohinani November 10th 2018 Conclusion: The results of my experiment showed that the rate of reaction for sucrose was the highest with an average of 3.2 cm3 per min of carbon produced. Followed was glucose which produced 2.8cm3 per min. then fructose which produced 2.4cm3 per min and finally lactose had no rate of reaction because no carbon was produced, therefore my null hypothesis was correct.
