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Yeast Respiration Lab

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“Investigate the factors affecting the rate of yeast respiration” Lab Report


The aim of this experiment was to investigate the effect of different amounts of a substrate on the respiration rate of yeast and to compare this to the effect of different amounts of glucose on the rate of yeast respiration. The substrate which I chose to further investigate was fructose. Fructose is a fruit sugar which is one of the three, along with glucose and galactose, dietary monosaccharides that are directly absorbed into the bloodstream during digestion.

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Apparatus 2% yeast solution

Large beaker Small beaker Conical flask Thermometer (? C) Glass rod pH meter & data logger Hot water Sensitive digital scale (g) Fructose (1. 0g, 1. 5g, 2. 0g, 2. 5g) Glucose (1. 0g, 1. 5g, 2. 0g, 2. 5g) Measuring cylinder (cm3) Variables Independent: Concentration of glucose (1. 0g, 1. 5g, 2. 0g, 2. 5g) , concentration of fructose (1. 0g, 1. 5g, 2. 0g, 2. 5g) Dependent: Amount of carbon dioxide produced, i. e. rate of yeast respiration Controlled: 2% yeast solution (20cm3), initial temperature of yeast solution (35-40? C), amount of time that the reaction is measured (180 seconds)


All apparatus was collected and safety precautions (hair tied back, safety goggles and lab coat) applied 20cm3 of 2% yeast solution was measured out, using the measuring cylinder, and poured into the conical flask 1.

0 ±0. 5g of glucose was weighed out on the sensitive digital scale Hot water was then poured into a large beaker into which the conical flask, containing the 2% yeast solution, was held in place in, with a thermometer inside The conical flask was held like this until the 2% yeast solution reached an initial temperature between 35-40C (specific temperature was noted down)

When this temperature was reached, the thermometer was taken out of the conical flask and the conical flask out of the hot water 1. 0 ±0. 5g of glucose was quickly added to the 2% yeast solution, inside the conical flask, and mixed only a little, enough to dissolve the glucose Meanwhile, the pH measurer was quickly placed into the conical flask and the data logger was started when the active ingredient, i. e. lucose, was added This setup was left until the data logger reached a time of 180 seconds, at which point it was stopped and the pH measurer was taken out of the solution and placed into a beaker with clean water to prevent build up.

The final temperature of the 2% yeast solution was measured and noted down to ensure that the temperature loss, in comparison to the other trials, would be the same and therefore not affect the results Steps 1-9 were repeated 2 more times to give a total of 3 Trials which ensured fair testing Steps 1-10 were repeated using different amounts of glucose (1. g, 2. 0g, 2. 5g) Steps 1-11 were repeated except that instead of glucose, fructose was used The pH meter measured the change in pH, which was recorded in the data logger and printed off as tables An average of each solution’s 3 trials was taken The data was then converted into graphs from which the gradient was calculated to give the rate of yeast respiration.

Quantitative Data

During reaction: Occasional bubbling in the glucose/fructose + yeast solution (CO2 bubbles produced during the respiration reaction). Graphs Data processing Conclusion

In this lab we tested the effects of different types of sugar and temperature on the release of CO2 in yeast. Through research, we learned that yeast uses the carbon in the sugar as a source of energy and produces CO2 through respiration. We hypothesized that adding different sugars would affect the rate of CO2 released, and that colder temperatures will decrease the amount of CO2 released by slowing down the yeast’s metabolism. Not really sure what you want answered – different respiratory substrates have different respiratory quotients (i. e. he amount of oxygen consumed/CO2 released though you wouldn’t have to worry about the former in anaerobic respiration. )In terms of *why* the rates of respiration are different for the different substrates – it’s down to enzymes. If you do Chemistry it helps because structural isomerism is involved. If you look at the chemical structures of fructose and glucose you’ll see that they have the same number of carbon, hydrogen and oxygen atoms etc – but the groups are arranged differently around the 6-carbon backbone. So fructose is a structural isomer of glucose.

Yeast uses enzymes (coenzymes – Krebs cycle an’ all that) for respiration that act on these substrates to release their energy. Enzymes have a specific shape of active site due to their unique tertiary structure. This will work for ONE isomer only – so an enzyme that works on glucose wouldn’t work for fructose because fructose is a different atomic shape. These enzymes (I think) are present in different concentrations. So the lower the concentration of enzymes specific to a particular substrate e. g. lactose or whatever, the lower the rate of respiration using that substrate.

The only difference between the two is that glucose has an aldehyde group (its C=O is at the end of the carbon chain) and fructose has a ketone group (its C=O is not at the end of the chain – it’s in the 2nd carbon position) Also the rates were abnormally high (but not constant), and then they reached a LOWER constant rate. So somehow the yeast was respiring fast to begin with and then sort of accommodated to the substrate and reached a constant rate of respiration. did you leave the yeast solutions to equilibriate in the water bath?

If not then the fluctuations in respiration rate may be due to the yeast adjusting their respiration in response to the temperature Evaluation Sucrose and lactose are not single sugars (mono-saccharides). They are di-saccharides or double sugars. Yeasts, and just about living every living thing has to break complex carbohydrates to simple sugars, namely to glucose then to fructose. Sucrose is a double sugar made of glucose and fructose linked together. The enzyme to break that double sugar into single sugars is fairly commonplace among living organisms (and certainly in yeast).

Plus, under slightly acidic conditions, sucrose will break into the two single sugars automatically. Thus, sucrose breaks down to glucose plus fructose. Lactose is a double sugar made of glucose and galactose linked together. That link is both strong and the enzyme is not so common (certainly not in common bakers yeast). Even some humans lack the enzyme needed to break lactose when they become adults. Thus, the answer to your question is: fructose has a head start on becoming carbon dioxide over glucose and sucrose. And because the yeast can’t break lactose into digestible pieces, there will be no carbon dioxide.

Cite this Yeast Respiration Lab

Yeast Respiration Lab. (2016, Oct 26). Retrieved from https://graduateway.com/yeast-respiration-lab/

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