Does temperature change affect the respiration of yeast?

Introduction: Cell respiration is the process by which cells are able to release energy. The process of cellular respiration can either occur in the presence or absence of oxygen and this will result different products. When oxygen is present (aerobic respiration) yeast cells use enzymes to convert glucose to carbon dioxide and water, releasing lots of energy in the process. When yeast cells respire without oxygen they use enzymes to convert glucose to carbon dioxide and alcohol (fermentation). The effect of temperature in cell respiration mainly depends on the effect of enzyme activity. As the temperature rises the rate of cellular respiration increases as enzymes in yeast work better in warmer conditions. However if the temperature is too high, the enzyme will denature and this will decrease cell respiration. Through out this experiment we will measure the amount of CO2 produced whilst increasing the temperature to see if it affects the respiration of yeast. Aerobic respiration: Glucose + Oxygen  Carbon Dioxide + Water + ENERGY Anaerobic respiration: Glucose  Ethanol + Carbon Dioxide + ENERGY

Hypothesis: The higher the temperature, the more carbon dioxide will be released by yeast, therefore forming a greater amount of bubbles. But once the temperature gets above a certain point the rate of respiration will decrease.

Explanation: When temperature increases, the enzymes in yeast work better (so respiration increases). Once temperature gets to a certain point enzymes denature (so the rate of respiration will decrease).

Variables: Independent: The changing temperatures of the water bath Dependent: Amount of Carbon Dioxide released in 1 minute (number of bubbles) Control:   

Same amounts of yeast (5ml) and glucose (10ml) solution Same period of time for counting the number of bubbles for each temperature, in this case 1 minute Covering each test tube with solution inside, completely with the hot water

Experimental Design: Delivery tube

Thermometer Carbon dioxide coming out as bubbles in water

Test tube fitted with bung with glucose solution and yeast. It is important that the water covers all solution Stopwatch

Pipettes used to measure 5ml of yeast and 10ml of glucose

Dried yeast

Test tube rack

Materials and Equipment:         

Water Bath Dried Yeast (48gm yeast 0.6dm3) Thermometer Timer Test tube rack Test tubes (one fitted with Hot water starting at 60 degrees Celsius Delivery tube Rubber connection and jet Glucose solution (5%)

bung)



Big beaker (400cm3)

Method: 1. Gather all of the apparatus required to set up a water bath 2. In a 400cm3 beaker pour 200ml of hot water 3. With a thermometer measure the temperature of water until 60 degrees is reached and work down wards 4. Using a pipette pour 5ml of yeast and 10ml of 5% glucose solution 5. Avoid mixing or shaking the test tube 6. Deposit the test tube in water bath covering it with a bung and its delivery tube 7. At the other end of the delivery tube, place another 400cm 3 beaker with tap water where the carbon dioxide bubbles will be seen as product. 8. With a timer record the number of bubbles you see every minute 9. Repeat steps 2-8 but with 50, 40, 30 and 20 degrees 10. Record your results

Results and process: Temperature (Degrees Celsius) 20 30 40 50 60

Graph:

Number of bubbles produced in 1 minute (CO2 released) 0 0 3 6 30

Does temperature change affect the respiration rate of yeast? 7

Number of bubbles

6 5 4 Number of bubbles produced in 1 minute (CO2 released)

3 2 1 0

-1

0

20

40

60

80

Temperature

Conclusion: In conclusion, our hypothesis was supported to some extent because our results clearly show how the number of bubbles released at 60 degrees was the highest compared to other lower temperatures. The graph shows a rising slope; where at 20 degrees no bubbles were emitted in comparison to 60 degrees. The difference is quite staggering and there is not a periodic increase in number of bubbles, this might be due to errors in the experiment. The yeast respires rapidly at higher temperatures than at lower and this can be explained due to the kinetic theory. At higher temperatures more heat energy is provided to the particles and they would move faster having more collisions in a certain amount of time (1 minute). Nevertheless 60 degrees is a pretty high temperature for respiration to occur as enzymes would denature causing them to be unable to bind with the yeast and glucose particles but in this case we could say that the test tube was just beginning to heat up with the yeast and so the actual temperature inside was not 60 degrees at all. Therefore, most of the CO2 was released here. Probably the optimum temperature for respiration of yeast would be between 40-50 degrees.

Evaluation: Errors:

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We did not repeat our results enough times to get a proper average and therefore our results are unreliable. We moved the test tubes around a lot and this biased the results for our respiration A proper water bath was not used so the temperature was not controlled precisely. 30 bubbles produced at 60 degrees could be seen as an anomaly as it is a lot of bubbles compared to the rest of the results, this was because the yeast was cold and it was just starting to heat up. This biased our experiment Try with yeast at room temperature as the one used was previously left on the fridge The yeast and glucose mixture was not the same temperature as of the water

Proposed modifications:      

Find an optimum respiration temperature for yeast which could be between 40 and 50 degrees, it would be nice to try the experiment for example at 45 degrees. Repeat results twice or three times to get mean Give more time for the respiration to occur. At least more than 1 minute. To be sure our solutions were not contaminated we could have worked in a much cleaner space, further away from other experiments We could have used more precise pipettes to have the correct amounts of solutions Next time we could try with a different type of yeast, not only dried yeast