Yeast Cellular Respiration Lab Report

Cellular respiration is defined as a sequence of metabolic processes by which living cells produce energy. Biochemical energy from nutrients are converted into adenosine triphosphate (ATP), which is essential for the energy of life. ATP transports chemical energy within cells for metabolism. Most cellular functions – synthesis of proteins and membranes, cellular division, etc. – need energy to be carried out. The reactions and steps that occur during cellular respiration include glycolysis, the Krebs Cycle and the Electron Transport Chain. Cellular respiration is a metabolic process which occurs in all living cells. There are two types of cellular respiration; aerobic and anaerobic. Aerobic respiration is more efficient and is utilised in the presence of oxygen, whereas anaerobic respiration does not require oxygen. Yeast is a single celled fungus and must produce its own energy to survive using either aerobic or anaerobic respiration. Sugars, which are carbohydrates, are used in the cellular respiration process in yeast, which can either be monosaccharides

or disaccharides. Yeast use enzymes, such as zymase, glucose and sucrose, to assist in the conversion of sugar into ATP and CO2.
The experiment focuses on the cellular respiration rate of yeast which was tested using different sugars.

The disaccharides were: maltose and sucrose. The monosaccharides: glucose, fructose and lactose. In the experiment, the amount of CO2 produced was recorded by a gas sensor over a period of fifteen minutes in a Nalgene bottle of 3mL yeast solution and 3mL of sugar solution. It was predicted that the disaccharide sugars would produce a higher rate of cellular respiration, however, this hypothesis was proven wrong during the experiment. The data revealed that glucose was the sugar that produced the largest amount of CO2 (236 ppm/min). It had 28.5ppm/min more than the second most efficient sugar fructose (208.3ppm/min), which is also a monosaccharide. The products of one molecule of glucose in glycolysis include six molecules of carbon, six molecules of water and energy molecules called ATP and NADP (Source

43).
Of the five sugars tested, glucose had the highest respiration rate. Based on research, disaccharides should have produced more CO2 than monosaccharides because they are made of two monosaccharides so they can be broken down into twice as much carbon dioxide and energy (Source 39). However, glucose, a monosaccharide, produced the most CO2 (Refer to graph 1 and 2). As shown in the Lactose Trials (page 22 of journal), lactose did not respire at a high rate. The average respiration rate of lactose was only 17.5ppm/min (shown in results table page 18 of journal). This is because most yeast do not contain the enzyme required to breakdown lactose, which is lactase. The enzyme lactase is absent in most yeasts, especially baker’s yeast, consequently they cannot break the lactose into digestible pieces resulting in the low production of CO2 as shown in the experiment. The compounds of yeast, including their enzymes explains why some sugars did not act well. The yeast used in the experiment must not have had the enzymes that are needed to break down the sugars that could not respire at a sigh rate such as maltose and lactose. The enzymes needed to break down these sugars are maltase and lactase.
Patterns in the data include a consistent rise of the gradient over the fifteen minutes, the correlation is as time increases so does the respiration rate. Because of removing the anomalies, the data is more accurate. As an extrapolation, the respiration rate would have continued to rise until optimal point was reached, then started to decrease in CO2 production as the yeast would have used up all the sugar in its process of cellular respiration. An outlier is an observation that appears to deviate markedly from other observations in the sample. Outliers may be due to random variation. There were two outliers in the trials, where there was inconsistency in the data. In graph 1 (page 18 of journal), sucrose has a higher respiration rate than fructose. However, with the anomalies excluded, fructose had a higher average of 208.3ppm/min. Based on the results in graph 1, fructose produced the third highest amount of CO2 in the respiration of yeast, with an average respiration rate of 152.6ppm/min. However, there were inconsistencies in the results with fructose having an outlier of 41.29ppm/min, which affected its overall average, making it lower. It was decided, after analysis, that the outlier would be removed from the data to produce more consistent results. Also, affecting its total average from 152.6ppm/min (graph 1) to 208.3ppm/min with the outlier removed (graph 2). These outliers may be present because of errors in the experiment or the limited amount of trial numbers.
Referring to secondary data on a similar experiment (Source 41), maltose and glucose were the highest CO2 producing sugars, their conclusion presents that glucose is a high producer of respiration because yeast is made of two glucose molecules. Another source of secondary data (source 49), concludes in their experiment that glucose was also the highest CO2 producing sugar. Glucose is directly used in glycolysis and does not require further energy to convert into a usable form, this supports the reasoning of why glucose, out of all the sugars, had the highest respiration rate of yeast. Glucose was the highest producing sugar in the experiment, proving the initial hypothesis wrong as glucose is a monosaccharide. Some of the errors that contributed to unfair testing included; not letting the gas censor warm up or cool down during trials, the amount of time yeast was left in the test tubes waiting to be used, water still left in Nalgene bottle/test tubes. Several the errors may have been a result of the uncontrollable variables; yeast behaving differently each day, variability in trials, current CO2 in the air. To make the experiment more fair and accurate in the future more control methods should be implemented and the executing more than three trials will produce more accurate averages.
The purpose of the experiment was to find which sugar produced the most CO2 regarding the cellular respiration in yeast. The hypothesis that was proven wrong in the experiment was; disaccharides would produce a higher rate of cellular respiration compared to monosaccharides. The hypothesis was wrong because glucose, a monosaccharide produced the highest amount of CO2, this is because not all sugars are equally utilized by yeast. Glucose is a high producer of respiration because yeast is made of two glucose molecules and is directly used in glycolysis and does not require further energy to convert into a usable form. It is concluded that glucose is the sugar with the greatest respiration rate (236.8ppm/min) and lactose has the least production of CO2 in yeast (17.5ppm/min). Lactose was the least efficient because most yeast do not contain lactase, the enzyme required to breakdown lactose. It is absent in most yeasts, resulting in the low production of CO2 as shown in the experiment. The evidence and data provided concludes that it sugars do not have to be a disaccharide to produce a larger amount of CO2, but that it depends on the enzymes in the yeast that are capable of breaking down these sugars in cellular respiration. Glucose is the most efficient sugar in producing the highest CO2 amount in the respiration of yeast.