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Biology Project

s. Biology Project. Effect of Different pH on Anaerobic Respiration of Yeast. Aim. To investigate the effect of different pH on anaerobic respiration of yeast. C. P. P. I. E. R. I. N. L. Yeast is a type of enzyme. Enzyme, which is made

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Biology Project

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  1. s Biology Project Effect of Different pH on Anaerobic Respiration of Yeast

  2. Aim To investigate the effect of different pH on anaerobic respiration of yeast.

  3. C P P I E R I N L Yeast is a type of enzyme. Enzyme, which is made up of protein, will denature in extreme pH and work best in its optimum pH, therefore, it should only work in a certain range of pH. Since enzyme will loss its biological function once denatured, changes in the rate of the anaerobic respiration is a very sensitive measure of denaturation.

  4. C P P I E R I N L When yeast carries out anaerobic respiration, it will give out both ethanol and carbon dioxide as bi-products. By putting yeast in solutions of different pH value and study the amount of gas (carbon dioxide) produced, which implies its rate of anaerobic respiration, we should be able to tell the range of pH it works best in.

  5. C P P I E R I N L To measure the amount of carbon dioxide produced， we can measure the pressure of the gas in a fixed volume of space， since amount of gas produced is directly proportional to the pressure it exerted on the container.

  6. Material Beaker(250cm3) × 3 Beaker(500cm3) × 3 Buffer solution of pH 4, 7 and 10 × 3cm3 each Computer × 1 Data logger × 1 Electron balance × 1 Glucose solution × 450cm3 Ice Measuring cylinder × 3 Oil High Pressure Sensor × 3 Thermometer × 3 Yeast × 1g

  7. Procedure: • 1. Computer was set up with data logger and sensors • connected, and the software Science Workshop • was chosen. • 2. 100g of glucose solution was weighted using the • electronic balance. Water was added to it to make • up a solution of 500cm3. • 3. Icy water was poured into the 3 500cm3beakers • to make 3 water baths in order to keep the • temperature of the solutions constant. • 4. 150cm3 of glucose solution was poured into 3 • 250cm3 beakers and 3cm3 of buffer solution of • different pH value was added to each of the • beakers separately. Procedure:

  8. Procedure: • 5. The 3 beakers of solution was then boiled. • After it was boiled, a layer of oil was added to • it and it was then put into the water baths. • Thermometers are put into the beakers of • solution to monitor the temperature. • 6. 0.3g of yeast was weighted and grinded into • small particles. It was then poured into the • syringe. The plunger was slowly pushed until • no room was left. • 7. After the temperatures of the 3 solutions • became 15oC, the syringe of yeast was • inserted into it to suck 15cm3 of solution up. Procedure:

  9. Procedure: • 8. The syringes were connected to the high pressure • sensors. • 9. Recording was started. Pressure in the three • syringes were adjusted by pulling out or pushing • in the plunger until they are of 100kPa. • 10. Recording was stopped. Previous records were • deleted. • 11. Recording was started again for 600s to plot a • graph of pressure against time. Procedure:

  10. This is the set up...

  11. Pressure of gas produced in solution of pH4， pH7， pH10 against time R E S U L T

  12. R E Yeast works best between neutral to slightly alkaline medium. S U L T

  13. Discussion From the graphs obtained, we can see that the enzymes in yeast will denature in acidic medium and work best in neutral and alkaline medium. When the pH of a solution containing protein is changed, the protonation state of the amino and carboxylate groups changes, and ionic bonds in the proteins will be disrupted. This will need to changes in the shape of the protein molecule that cause it to loss its biological function. The protein is then said to be denatured.

  14. Discussion Since yeast is made up of protein, if the protein denature, the yeast can no longer respire. The pressure of gas produced in fixed volume of space during anaerobic respiration reveals the ability of anaerobic respiration of yeast, which in turns reveals the ability of protein to resist denaturation. From the graphs obtained, we see that the proteins which made up yeast is capable to work in both neutral and alkaline medium.

  15. E r r o r s Small amount of oxygen present in the syringe Increase the volume of the mixture to reduce the percentage error. Difference in starting pressure affects the experimental result. Increase or decrease the volume of the syringe so as to split the different.

  16. E r r o r s Yeast is not totally dissolved Grind the yeast before mixing it with the solution to increase its surface area which enhance better dissolution. Slight difference in starting temperature Put all the solutions in one water bath instead of three.

  17. Conclusion Yeast works best between neutral to slightly alkaline condition.

  18. Member List Sandy Au Yeung (1) Stephanie Cheung (6) Winnie Ip (13) Bernice Law (14) Amy Wu (28) 6AS

  19. The End

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