BIOLOGY

1. BIOLOGY

3. Content • Aim • Biological principle • Apparatus • Procedure • Discussion • Improvement • Conclusion

4. Aim: To investigate the anaerobic respiration rate of yeast in different concentration of glucose solution Biological Principle: 1.In the absence of oxygen, yeast will undergo anaerobic respiration .Yeast converts glucose into ethanol and carbon dioxide. So, the carbon dioxide given out reflect the rate of anaerobic respiration. 2.Glucose was fermented because this sugar can pass rapidly into the cell and enter directly into metabolic pathways

5. Apparatus: Yeast Glucose powder Ice Conical flask Bunsen Burner Co2 Sensor Paraffin oil Beaker Laptop Computer Electron beam balance

6. 4 grams of yeast was measured by the electronic balance.

7. Percentage of glucose solution Volume of water added (cm3) Mass of glucose added (g) 3% 145.5 4.5 6% 141 9 9% 136.5 13.5 0% (control set-up) 150 0 Glucose solution was prepared in a beaker

8. The glucose solution was boiled under the Bunsen flame This glucose solution was cooled down by the Ice

9. Glucose solution was then mixed with the yeast in the reagent bottle under the water bath with temperature 30 oC. A layer of oil was added on the top of the solution . The Cardon dioxide Sensor sealed the reagent bottle. The reagent bottle was put under the water bath for 10 minutes.

10. DiscussionThe experiment is conducted to investigate the rate of anaerobic respiration in different concentration of glucose solution. When the yeast is put into the glucose solution without the presence of oxygen, the yeast carries out anaerobic respiration.The independent variable is the concentration of glucose. The dependent variable is the CO2 given out. Yeast is capable of utilizing glucose as respiratory substrate.As the yeast fermented glucose, bubbles of carbon dioxide are evolved, which rise to the top of the reagent bottle. The rate of carbon dioxide production varies with the concentration of the substrate. The CO2 given out reflects the rate of anaerobic respiration of the yeast.

11. Results: Table showing the concentration of co2(ppm) given out under different concentration of glucose solution

13. From the graph, the slope of the rate of anaerobic respiration of the 9% glucose solution is greater than that of 6% and 3%. As the concentration of substrate, glucose, increases, the rate of reaction increases. Yeast in the 9% glucose solution is the greatest, so the rate of reaction is the greatest. Yeast in the 3% glucose solution is the lowest, so the rate of reaction is the lowest. The low initial rate of CO2 production in the 3%, 6% and 9% glucose shows that time is needed for the synthesis of the enzymes for the breakdown of the respiratory substrate.

14. Improvement:After the glucose solution has been boiled to remove all the dissolved oxygen, the solution is cooled down and transferred to the container of CO2 sensor. However, some oxygen will dissolve in the solution during this transfer. That means aerobic respiration may occur. We can prevent it by heating the glucose solution in a container with a narrow neck, which suits the size of the CO2 sensor. And record the rate of fermentation by inserting the sensor into the container directly.Thus, the oxygen won’t be able to dissolve into the solution because transfer is not needed.

15. ConclusionFrom this experiment, when the concentration of glucose solution increases, the rate of fermentation increases.

16. 6B Rachel Chan (3) Christine Cheung(8) Iris Ma (20) Kelly Tam (26) 6AS Rondy Tai (21) (2001-2002)