Effect of type of sugar on rate of cellular respiration in yeast

Being passionate about cooking and especially baking, I know the process of using yeast mixed with flour and sugar to make breads and cakes. Yeast are used in the process as they ferment complex carbohydrate units and release carbon dioxide which causes the bread to rise up. This process is aerobic in nature as oxygen is utilized in the process where yeast undergoes cellular respiration. During such process, yeast releases carbon dioxide and energy. The type of sugar used in such process plays a major role as the type of sugar is not same everywhere. From the industrial aspect, it is that the process is fast enough. The purpose of this investigation is to understand whether the type of sugar used has any effect on the rate of cellular respiration or not. The rate of such process can be monitored by quantitative measurement of the carbon dioxide evolved during the process. Thus, I decided to narrow down my Internal Assessment in Biology on the research question phrased below-

Does the rate of cellular respiration (measured in terms of amount of carbon dioxide evolved per min over an interval of 30 minutes) in yeast (Saccharomyces cerevisiae) depends on the type of sugar (sucrose, fructose and glucose) used?

Yeasts are unicellular globular shaped fungi. They have the ability to produce energy on fermentation of carbohydrates through respiration. This can happen both is presence and absence of oxygen. The respiration that happens in presence of oxygen is aerobic respiration and the chemical equation is for that is as follows:

Glucose + Oxygen\(\rightarrow\) Carbon dioxide + Water + ATP (energy)

The same process is recognized as an anaerobic respiration when it happens in absence of oxygen and the equation is as follows:

Glucose\(\rightarrow\) Ethanol + Carbon dioxide + ATP (energy)

It must be noted that carbon dioxide is evolved as a by product in both aerobic and anaerobic respiration. Anaerobic respiration is also known as fermentation. As alcohol (ethanol) are produced during fermentation, this is also known as alcoholic fermentation. In both cases, energy is produced as ATP molecules. The amount of energy produced during aerobic respiration is much higher than that in anaerobic respiration.

The current investigation is focused on aerobic respiration which is a cellular process happening in yeast.

Aerobic respiration in yeast follows a catabolic pathway comprising mainly of four different steps- Glycolysis, Link Reaction, Kreb’s cycle and chemiosmosis. The release of carbon dioxide from the cell wall happens during the last stage which is chemiosmosis. Due to combustion process happening inside the cell, the osmotic pressure is higher inside the cell which causes the carbon dioxide to be released out of the cell. The release of carbon dioxide from the cell wall during cellular respiration results in the formation of foam. Hence, the rate of respiration can be monitored by both measuring the rate at which carbon dioxide is evolved as well as the amount of foam produced.

Yeast secretes a lot of enzyme during each and every step of the aerobic respiration. As enzymes gets denatured (loses their shape and cannot bind to the substrate) at high temperature, controlling temperature during this process is essential. The process is carried out at 40.0oC as that has been reported to be the optimum temperature of fermentation.

The amount of foam produced can be measured in terms of amount of Carbon dioxide at regular intervals of time and the values can be plotted against the time. The rate of the reaction can be determined from the gradient of such plots.

A literature review of a research article on the title¹ - The effect of different sugars in the medium on carbon dioxide production in Saccharomyces cerevisiae by Jason Angustia, Maggie Chan, Deirdre Dinneen, Shamim Hortamani, Diane Mutabaruka reveals that the rate of cellular respiration is higher for glucose and fructose in comparison to sucrose. The level of CO₂ produced was recorded as a function of time for four different types of sugars – glucose, maltose, fructose and sucrose. The image below² is a snap shot of the data table of that research article in support of the statement written above.

There is no correlation between the type of sugar used and the rate of cellular respiration.

There is a correlation between the type of sugar used and the rate of cellular respiration.

• Yeast
• Glucose – 10.00 g
• Sucrsoe – 10.00 g
• Fructose – 10.00 g
• Distilled water – 1000cc

• Yeast is not a harmful organism but inhalation or direct ingestion is not recommended. Thus a physical barrier with the microorganism is essential to avoid any sort of cross contamination. Protective clothings like safety gloves, lab coats were used.
• None of the materials used were ingested or exposed to skin. Eatables were not allowed inside the laboratory as the microorganism used might infect them.

The methodology adopted or the issue at which the investigation is focused on does not have any ethical issues.

18.00 ± 0.01 g (0.1 moles) of glucose was weighed on a watch glass using a digital mass balance. The weighed solid was transferred to a neat and dry 100 cc volumetric flask and dissolved in 100 cc distilled water.

Similarly, aqueous solutions of sucrose and fructose were prepared by dissolving 34.2 g of sucrose and 18.0 g of fructose in 100 cc of distilled water.

• A 250 cc glass beaker was taken and filled with 50 cc of the glucose solution.
• 5.00 ± 0.01 g of yeast was weighed on a watch glass using a digital mass balance and added to it.
• The stop-watch was started.
• The amount of CO₂ produced was then measured after 5 minutes using a CO₂ gas sensor.
• The gas sensor was calibrated before use.
• The measurement of CO₂ produced was continued till 30 minutes at an interval of 5 minutes.
• Steps 1-5 were repeated for four more times to collect data in five sets.
• Steps 1-6 were repeated for other two solutions – sucrose and fructose.

•  The sugar solutions used were transparent and clear.
• Addition of yeast to the sugar solution turned the solution turbid. 
• With the progress of time, the solution turned more turbid and more foam were produced.

Average amount of CO₂ evolved in ppm ( for 300.00 s) =\(\frac{300+310+300+320+330}{5}= 312.00\)

Standard deviation = \(\frac{(300-312)^2+(310-312)^2+(300-312)^2+(320-312)^2+(330-312)^2}{5} = 13.04\)