The effect of temperature on the activity of yeast
AIM
The aim of the experiment is to determine the optimum temperature when yeast produces the biggest volume of carbon dioxide and investigate the effects of temperature on the respiration of yeast in a glucose solution.
Hypothesis
The prediction is that the optimum temperature is 45℃ because if the temperature is high enough, respiration increases and the enzymes in yeast work better, then more carbon dioxide will be released by yeast.
Introduction
Yeasts are eukaryotic unicellular microorganisms that belong to a group of simple organisms known as fungi. Yeast microbe is probably one of the earliest domesticated organism. (Barnett, 2011)
In 1680, Antonie van Leeuwenhoek was the first one who visualized yeast utilizing high quality lenses. Charles Cagniard de la Tour, in 1835, used a more efficient microscope to prove that they are single celled organisms. Theodor Schwann identified yeast as fungi in 1837. (Ainsworth, 1976)
Yeasts have an important role in brewing and baking. The ethanol produced by yeast makes wine and beer alcoholic and the carbon dioxide makes bread dough rise. (Bamforth, 2008) Yeast is also used in pharmaceutical industry as source of enzymes, in antibiotics, in nutritional supplements and in vaccines. (Ostergaard S and Olsson L, 2000)
Yeast uses sugar as food source and produces energy required for survival and reproduction through the disintegration of sugar molecules. Glucose is one of the monosaccharides that are small enough to pass through the cell membranes of yeast. This simple sugar is usually used in experiments as a control. (Piškur and Compagno, 2014)
Yeast can metabolize sugar in two modes, aerobically, requires the presence of oxygen or anaerobically, without oxygen. Anaerobic respiration takes place in cytoplasm, while most of aerobic respiration takes place in mitochondria. (Mukerjee and Arunima, 2008)
Glycolysis appears in both types of respiration, but aerobic respiration implicates Electron Transport Chain and Krebs cycle, while anaerobic includes only fermentation after glycolysis. (Piškur and Compagno, 2014)
Anaerobic respiration uses glucose and no oxygen and converts it into alcohol or lactic acid and CO_2.
Glucose → ethanol or lactic acid + carbon dioxide + energy
C_6 H_12 O_6 →2C_2 H_5 OH+2CO_(2 )+2ATP
Aerobic respiration uses oxygen and glucose and transforms it into water and CO_2, releasing 36 ATP (adenosine triphosphate).
Glucose + oxygen → carbon dioxide + water + energy
C_6 H_12 O_6+ 6O_2 → 6CO_2+6H_2 O+36 ATP
Figure 2. Anaerobic vs. Aerobic pathways (SparkNotes LLC, 2013)
Yeast cells produce chemicals named enzymes (ferments), which are specialized proteins that serve as catalysts, speeding up the procedure. Enzymes have an optimal temperature range too. If the temperature is too high, the enzyme will deteriorate and this will decline cell respiration. If the temperature is too low, usually the enzymes are not inactivated, but just work slower. (Barnett, 2011)
Method
The experiment followed CUC Protocol.
Figure 3. Apparatus for measuring the production of carbon dioxide
Health and Safety procedures were respected: personal items were kept in the area provided, long hair was confined, laboratory coat and protective equipment (gloves, eye protection) were worn and removed before leaving the laboratory, and hands were washed after completion of laboratory procedures.
RESULTS
Volume of 〖CO〗_2 produced (〖cm〗^3)
Time (minutes) 20℃ 35℃ 45℃
0 0 0 0
10 11 26 51
20 24 84 100
30 37 100 100
40 54 100 100
50 73 100 100
60 86 100 100
Figure 4. The table represents the amount of 〖CO〗_2 produced every 10 minutes for an hour
Figure 5. The graph illustrates the results of 〖CO〗_2 produced every 10 minutes for an hour, with different temperatures
The graph above shows the results of the practical.
The most and fastest 〖CO〗_2 produced it was at 45℃. In 10 minutes, was collected 51 〖cm〗^3 〖CO〗_2 and after this point, the amount of 〖CO〗_2 reach 100 〖cm〗^3. The average at this temperature was 91,8 〖cm〗^3.
The graph shows that at 35℃, in 10 minutes was produced 26 〖cm〗^3 〖CO〗_2. In 20 minutes was released 84 〖cm〗^3 〖CO〗_2 and then in 30 minutes the amount of 〖CO〗_2 achieved the limit of 100 〖cm〗^3. The average at this temperature was 85 〖cm〗^3.
At 20℃ (ambient temperature), the graph shows that in 10 minutes was produced only 11 〖cm〗^3 of 〖CO〗_2. In 20 minutes was released a value of 24 〖cm〗^3 〖CO〗_2, in 30 minutes 37 〖cm〗^3 〖CO〗_2, in 40 minutes 54 〖cm〗^3 〖CO〗_2, in 50 minutes 73 〖cm〗^3 〖CO〗_2 and in 60 minutes the amount of 〖CO〗_2 was 86 〖cm〗^3. The limit of 100 〖cm〗^3 〖CO〗_2 was not reached. The average at this temperature was 47,5 〖cm〗^3.
DISCUSSION
This experiment was designed to prove the impact of temperature on the rate of metabolism of yeast.
The rate of cellular respiration is affected by the conditions in which it takes place. There are results obtained in 3 different temperatures: 20°C, 35°C and 45°C.
At 20°C (ambient temperature) was obtained an average of 47,5 〖cm〗^3 〖CO〗_2 in 60 minutes. In one hour, the limit of 100 〖cm〗^3 was not reached. The release of 〖CO〗_2 at this temperature was slowly because the temperature did not allow enzyme to work properly. The results might be inaccurate because the solution was improperly mixed.
The volume of 〖CO〗_2 collected at 45℃ showing that at high temperature, more carbon dioxide was released in less time. The limit of 100 〖cm〗^3 was reached in 20 minutes. This could be explained by kinetic theory. Kinetic theory says that with an increase in temperature, the rate of reactions will increase. When something is heated then the particles move faster increasing collision frequency and there will be more collisions between the substrates and the enzyme and so the reaction will appear faster. (Grad, 1949)
At this temperature, the enzyme break down easier and then transform into energy quicker. The temperature of maximum efficiency is about 45-50°C. This is called the optimum temperature. After this point the enzymes can become denatured.
The experiment run aerobically to certify that the carbon dioxide was produced rather than ethyl alcohol. (Mukerjee and Arunima, 2008)
In the experiment might be some errors and there are changes that could be made to enhance the quality of the results. It is important that the solutions used are not contaminated and the experiment takes place in clean space to get more accuracy. A better overall result would be achieved by repeating the experiment more times.
Conclusion
In conclusion to this experiment, hypothesis was accepted because results clearly show that the temperature affects the activity of yeast.
Using different temperatures was determinate that at higher temperatures more 〖CO〗_2 was released in less amount of time. The optimum temperature would be 45°C and this can be sustained by the kinetic theory.
References
Ainsworth, G.C. (1976) Introduction to the history of mycology. New York: Cambridge University Press
Bamforth, C.W. (2008) Food, fermentation and micro-organisms. United States: Wiley-Blackwell
Barnett, J.A. and Barnett, L. (2011) Yeast research: A historical overview. Washington, DC: American Society for Microbiology
Grad (1949) ‘On the kinetic theory of rarefied gases’, Communications on Pure and Applied Mathematics
Mukerjee, Arunima (2008) Cell Biology : Fundamentals & Applications. Oxford Book Co
Ostergaard S., Olsson L. (2000) Microbiology and Molecular Biology Reviews. (64 Vols). American Society for Microbiology
Piškur J., Compagno C. (2014) Molecular mechanisms in yeast carbon metabolism. New York, NY, United States
SparkNotes LLC (2013) Anaerobic vs. Aerobic pathways Available at: http://www.differencebetween.com/difference-between-aerobic-and-anaerobic-glycolysis/ [Accessed: 1 December 2016]
The structure of a glucose molecule (2015) Available at: http://www.hobart.k12.in.us/jkousen/Biology/biochem.htm [Accessed: 29 November 2016]