Yeast is both a singular and a plural name and is also is known as Saccharomyces Cerevisiae and even the sugar-eating fungus. Yeast is a eukaryotic, single-celled microorganism. As it is a fungus, yeast is usually found in warm, moist conditions. Yeast uses sugar for energy in cellular respiration. A great place to find yeast naturally is in/on sugary fruits. Yeast, bakers yeast in particular, is usually activated through being exposed to water while sugar gives it the energy to create CO2. The end product of this fermentation and cellular respiration process is CO2 and ethyl alcohol (CH3CH2OH).
This study is to investigate the cellular respiration of yeast (Saccharomyces Cerevisiae) in 5 separate temperatures (10°C,20°C,30°C,40°C,60°C).
The higher the temperature of the water surrounding the yeast, the faster the CO2 production will be in the cellular respiration to a point. After this point has been reached the production should slow and stop due to the denaturing of the enzymes. Since Saccharomyces Cerevisiae is usually found on fruit in the sun, the likely temperature that it would produce the most CO2 would be between 30°C and 60°C.
Independent variable – The changes in temperature of the yeast mixtures in 5 different conditions : 10°C,20°C,30°C,40°C,60°C.
Dependent variable – The change in height of the yeast mixture measured in cm.
Marking where the yeast mixture was before put in the water bath then again after, using this to measure the change in height.
Keeping all trials in the water bath for the same amount of time while timing using the same timer.
Keeping the temperature of the yeast the same throughout each trial.
Keeping the same environment for all tests.
Same batch of yeast.
Same amounts of flour, sugar and water in each mixture.
Same sized and shaped boiling tubes.
Same start volumes of mixture (using a syringe).
Gather things needed for this experiment e.g.
2 big bowls or pots (for the water bath and to mix the yeast mixture)
5 boiling tubes (to hold the yeast mixture)
A utensil to mix the mixture with.
Hot or cold water on hand from the fridge or a kettle
A whiteboard marker or sharpie (to mark the points and heights of the yeast mixture, if you use the sharpie make sure to have something to get the mark of the glass such as nail polish remover)
A thermometer to check the temperature of the yeast and water bath.
A big syringe with a blunt tip ( to easily get the mixture from your bowl to your test tube)
Measuring tube (to measure out the water)
Scale to measure out flour, sugar, and yeast.
Get your 5 boiling tubes ready to put the mixture into.
In your water bath wait to add the temperature appropriate water (independent variable) such as 10°C,20°C,30°C,40°C,60°C until just before you add the water to your yeast mixture.
Mix thoroughly together and sort some of the mixture into the 5 boiling tubes using the syringe (around 10 mL per boiling tube)
50g of flour
15g of sugar
3g of yeast
add the 60 mL of warm water (35°C) to the mixture then mix. Put temperature appropriate water into the water bath.
Measure and mark where the height of the dough is before you put it into the water with a ruler at eye level.
Put the boiling tubes in the water bath (aka bowl) then start the timer for 30 minutes.
As the time passes consistently measure the heat of the yeast with a thermometer and add hot or cold water to keep the temperature of the yeast constant.
Keep an eye out for CO2 bubbles that may escape.
When 30 minutes has passed take the boiling tubes out of water bath then measure and mark the height that it has risen with the same ruler at eye level.
Make sure to clean out the test tubes and dry them before every trial.
Repeat steps 2-10 for the different temperatures.
As seen in the graph above, which shows the individual change of height in centimeters of yeast mixtures placed in different temperatures going up in tens. The higher the temperature of the mixture of the yeast the higher the amount of change in height of said mixture which supports my initial hypothesis. Although there is a significant amount of overlap, the variation increases the higher the temperature increases and the data becomes closer together the lower the temperature decreases. Though there is a moderately clear difference between the changes in height at different temperatures showed by the box and whisker graph below, which means there is an extremely clear difference between 10 °C and 60 °C as they don’t overlap over each other. For 10 °C the average change in height was 0.145 cm, for 20 °C the average change in height was 0.46 cm, for 30 °C the average change in height was 3.32 cm, for 40 °C the average change in height was 5.34 cm and for 60 the average change in height was 6.185 cm. As shown in the last graph, which shows the average change in height for the different temperatures, this data also supports my hypothesis as the data points follows the regression line increasing with a correlation coefficient of 0.13551. This means for every 10 °C the temperature of the solution increases the change in the height of the solution increases by approximately 1.35 cm. The data becomes less reliable after 50°C as the range increases.
The data I have obtained throughout this experiment, shown in the previous graphs and tables, supports my hypothesis. The increase in temperature of the yeast mixture will cause the mixture to rise at a faster rate in the 30 minutes given in the separate temperatures ranging from 10 °C to 60 °C as yeast will react to the environmental factor (heat) as the water along with the food source (sugar and flour) allows for fermentation and cellular respiration. These graphs also shows the change in the height of the yeast mixture which means the speed (on average) changes from (10 °C) 0.00289 m/h to (60 °C) 0.123 m/h.
According to research done in “Scribd” by Lex Shelton, she conquered that the effect of temperature on the cellular respiration of the yeast mixture majorly affects the time it takes for the yeast to finish fermentation “When the yeast was in an environment that was warmer than the ideal temperature range, the amount of time it took to ferment was also shorter”.
Yeast creates a larger amount of CO2 in higher temperatures but once it reaches temperatures around 70 °C the mixture produces less and creates a large range of data as the yeast is killed. The higher of the temperatures to a point allow the enzymes in the yeast to move faster also leading to more CO2 produced and a higher fermentation rate. When this CO2 is produced, because of the stretchiness of the flour and water, the CO2 gets trapped and causes the mixture to rise. In this investigation from scribd instead of having a mixture that traps the CO2 they have a machine that calculates the amount of CO2 with a computer. This process occurs in nature when fruit such as berries become ripe due to time and break open. Dew to the sugar content within these microorganisms work to ferment them. Some animals seek out these fruits as they become alcoholic. The temperature that produced the most CO2 in the amount of time given was 60°C but I noticed that the mixture rose very fast but then not at all, while the temperatures 30°C and 40°C rose consistently over the 30 minutes. 10°C and 20°C almost didn’t rise at all leading to only minor changes near the end of the 30 minutes. Supported by GCSE Science on wiki books that this happened to the higher temperatures because of “the rapid expansion of gas” caused by the higher temperatures so it can be concluded that the yeasts production of CO2 increases the higher the mixture is till the point where the cells denature.
To make sure the choices throughout the investigation were valid, including my analysis and conclusion,the method and control variables were planned in a way to try and remove all errors that could arise. This will effect how accurate and reliable my results are, depending on how fair my testing was. Making sure other factors that could contribute to the cellular respiration of the yeast mixtures did not effect the results and hypothesis of ” The higher the temperature of the water surrounding the yeast, the faster the CO2 production will be in the cellular respiration to a point”. This will be done by having my only independent variable as the change in temperature of the different yeast mixtures and following to try and control everything else that has been listed in my control variables.
Temperature was controlled by measuring the heat within the mixtures with a thermometer and adding hot or cold water to the surrounding water bath to make sure the wanted temperature stayed constant. I measured the temperatures of the mixtures not the water bath because the two may not have been the same. Also having the same temperature water added when first mixing the yeast mixture to help with accuracy and validity. For example all water added to first mix the mixtures was 35°C. To increase validity next time or when being repeated I would recommend using a electronic water bath as this will keep the mixture at the same temperature without needing to add hot or cold water to it therefore decreasing human error.
To make sure the measurements were controlled and accurate the boiling tubes were marked to create points before and after being put into the water bath with a marker. These points were then measured in centimeters with a 30 centimeter ruler which was used throughout the experiment. All measurements were taken at eye level to avoid parallax error. This allowed the data to be more reliable as you could see the change from even 0.1cm. The equipment to create the mixture such as flour and sugar were measured using a electronic scale (that was zeroed) to get the same amount every time to the point. The liquid was also measured using a measuring tube (mL) also at eye level to avoid any human error.
The time of 30 minutes for each trial was taken using a timer, the same timer was used throughout the experiment. Using the same timer every time reduced error and having it on a countdown reduced human error as i’m not the one stopping it once it gets to thirty minutes as it does it itself.
Since the data was collected over three days all the doors and windows shut, having the heat pump on throughout all experiments at the same temperature (20 °C) to allow for the same room temperature throughout the entire investigation
I believe that my data is valid and reliable as I made 20 trials for five different temperatures (100 trials overall for 10°C,20°C,30°C,40°C,and 60°C) using all of the same equipment repeatedly, therefore there is enough data collected to see a pattern between the different temperatures. I also took the steps needed to make sure the yeast is only reacting to the heat surrounding it from the water bath. If this method and experiment were to be repeated I would expect the same type of results with a slight difference if a electronic water bath is used.