Effect of temperature on the rate of respiration of yeast in aerobic conditions

Since my childhood, I have been extremely fond of baked foods. The appetite for breads, cakes and other bakery foods has intrigued me to learn a little bit of the ways to prepare them. During my baking classes from my mother, who is an expert in this I was introduced to the fact that a certain microorganism- yeast is an unavoidable ingredient for this and my mistakes while baking a cake taught me that the temperature at which baking is done and amount of yeast added plays a major role in controlling the volume of the cake as well as its flavor. Further knowledge during my Biology classes at IB Diploma Program especially in the sub-topic enzymes, my concept in this arena became a little clearer. This exploration and a childhood interest coupled with my hobby of baking cakes has finally led me to select the topic of effect of temperature on rate of respiration of yeast in aerobic conditions as my topic of investigation for my Biology Internal Assessment.

How does the rate of aerobic respiration in yeast depends on the temperature at which it is carried out, determined using carbon dioxide gas sensor?

Yeast can respire in both aerobic (in presence of oxygen) and anaerobic (absence of oxygen) pathways.

Aerobic respiration is an enzyme controlled process. It occurs in two parts- Glycolysis and Kreb’s cycle and each step in this process are controlled by enzymes.

The enzymes used in this experiment is a multi enzyme system. The process is divided into two separate cycles- glycolysis and Kreb’s cycle. All steps in each of the cycle are catalysed by specific enzymes. Glycolysis converts glucose into pyruvate and then into Acetyl CoA using the enzyme pyruvate dehydrogenase.   The aerobic respiration occurs in several steps; catalysed by specific enzyme from the system in each step. The functioning of this enzyme depends on physical conditions like pH, temperature. Beyond a temperature (optimum temperature) the enzyme gets denatured and loses its shape. Hence as per the Lock and Key mechanism, it cannot function any more. The production of carbon dioxide reaches a constant volume and the rate of respiration becomes a limiting factor.

Null hypothesis: The variables rate of respiration in aerobic mode and the temperature has no correlation.

Alternate hypothesis: Both the variables rate of aerobic respiration and temperature have significant level of correlation.

NA= Not Applicable

• Weigh 3.42 g ( 0.01 moles) of  crystals of sucrose using a watch glass and digital mass balance.
• The weighed crystal was transferred into a 100 cm³ volumetric flask.
• Distilled water was added up to the mark.
• The sucrose was allowed to dissolve.

• 20 cm³  of yeast solution, was taken using the measuring cylinder from a beaker containing it  and transfer it to the jar.
• 20 cm³ of the sucrose solution was taken using a measuring cylinder, and transferred to the same jar, thus creating the ratio 1:1
• The jar was kept in the freezer to set the temperature of the solution at O°C.
• The gas sensor probe was inserted into the solution and timed for 3 minutes using a stop-watch.
• The same procedure was repeated for other temperatures created using the Bunsen burner.

• Protective clothing like gloves, lab coats were used.
• None of the chemicals were ingested or exposed to skin.
• The yeast solution was handled carefully.

• All waste liquids were disposed off safely into the waste bin so that the environment is not harmed.
• Emission of carbon dioxide was within a closed vessel which did not escape into the atmosphere and thus do not harm it.

• Minimum amount of chemicals were used.
• Minimum amount of microorganism yeast was used.

Sample calculations:

Calculation of mean value = (24.66 + 81.66 + 142.00 + 172.66 + 183.33) /5 = 120.86

Median value = Value in the middle position = 120.86