A. Introduction 1. Aim of experiment To investigate the effect of temperature on the rate of anaerobic respiration of yeast. 2. Reaction Yeasts respire anaerobically to break down glucose into carbon dioxide and ethanol. 3. Relevant Background Knowledge Heat provide the yeasts with the energy to undergo anaerobic respiration, but high temperatures may denature the enzymes in the yeasts such that the yeasts are unable to break down glucose in the absence of those enzymes. Low temperatures render those enzymes inactive. 4. Relate method of measurement to dependent variable.
When yeasts break down glucose, carbon dioxide is given out as a by-product. By counting the number of bubbles that emerge from the modified syringe in 1 min, the rate of yeast respiration can be calculated. 5. Expected trend As temperatures increase to optimum, there will be more bubbles evolved with 1 min and rate of respiration increases. However, when temperatures increases beyond optimum, the number of bubbles evolved will drop and rate of respiration decreases. These are so when glucose is in excess and all other factors are kept constant.
The initial increase in the rate of respiration is because as temperatures increase, average kinetic energy of the yeasts’ enzymes and glucose increases, increasing the frequency of effective collision between the enzyme’s active site and glucose. Hence more enzyme-substrate complexes are formed per unit time and more CO2 is produced, increasing the rate of respiration. However, when temperatures increase beyond optimum, the yeasts’ enzymes become increasingly denatured such that the shape of glucose is no longer complementary to its active site and can no longer fit.
Hence, less and less enzyme-substrate complexes are formed per unit time, less CO2 is formed per unit time and the rate of respiration decreases. B. Experimental Variables Independent Variable: Temperature of water in the boiling tube in which the modified syringe is kept submerged in. Range: 0 °C, 20 °C, 40 °C, 60 °C, 80 °C Dependent Variable: Number of bubbles evolved in 1 min Controlled Variable Quantity Concentration of yeast/ glucose mixture 2 % (w/v) yeast, 0. 5 cm3 2 % (w/v) glucose pH 2 cm3 of pH 7. 0 buffer, 0. 5 cm3 Volume of air in the syringe 1 cm3.
Time taken for reaction 1 min C. Experimental Procedure Procedure 1. Conduct a pilot test to determine to suitability of apparatus, optimum conditions and the amount of materials used. 2. Incubate the yeast and glucose suspensions in 0 °C for 5 min. 3. Pull the plunger of the modified syringe to 1 cm3 to contain air before drawing 0. 5 cm3 of well mixed 2 % (w/v) yeast solution. Draw up a further 2 cm3 of pH 7. 0 buffer. Place the plasticine at the end of the plunger. 4. Prepare water/ice at 0 °C in a 500 ml beaker. Measure the temperature using a thermometer to check.
Add some water into a boiling tube. Using plasticine, ensure that the syringe is upright. 5. Using the modified syringe, draw up a further 0. 5 cm3 of well mixed 2 % (w/v) glucose solution. Shake well and insert the modified syringe into the boiling tube, with the tip facing up. Ensure that the syringe is fully submerged and that the water level in the beaker is higher than in the boiling tube. 6. Start the stopwatch after 1 min to wait for number of bubbles evolved to remain consistent. Count the number of bubbles evolved within 1 min and record the results in a table.
7. Repeat steps 2 to 5 for 20 °C, 40 °C, 60 °C and 80 °C of water obtained by mixing varying amounts of hot water and ice to obtain the temperatures, checked using a thermometer. Labeled Diagram Producing Reliable Results 8. For each temperature, repeat the entire procedure two more times to obtain two more sets of readings. 9. Repeat the entre experiment two more times. 10. Carry out statistical tests such as chi squared or t-test, to determine whether there is any significant difference between the means. Positive control 11.
Positive control is subjected to the same conditions as that for the experiment except that temperature is adjusted to 37 °C, which is the optimum for yeast respiration. It serves as a reference point for the rates of respiration obtained in the range of the independent variable. Data Manipulation 12. The number of bubbles evolved from the modified syringe in 1 min is converted to rate of respiration by the equation: R= 1/N 13. A table for the collection and process of data is shown: Table showing the effect of temperature on the rate of respiration Temperature, T/ °C Number of bubbles evolved after 1 min, N Rate of respiration, R/ s-1.