Elements of ecology

Yeast Culture Lab



Yeast Lab

Yeast, is a microscopic one celled organism that belongs to the group of organisms that is called fungi. They are single celled organisms that have a scientific name of Saccharomyces cerevisiae. Yeast can have many purposes but the main purpose of yeast is to help the fermentation process. Yeast is a living organism known as a fungus and it gets its energy source from sugar. Yeast can also be used in creating certain medical intentions that heal wounds and reduce inflammation because of the large amount of hormones and enzymes.

In reference to yeast reproduction depends on the type of species because they can be either asexual by mitosis or sexual by budding. Consumption talked about the use and rate of use of a primary consumer that needs photosynthesis in order to create energy from CO2. Death is in reference to a population and refers to the toll of death in a population.


This labs main objective is to test cultures referring to yeast. The hypothesis is that the yeast will grow in all the environments that it is placed in but it will thrive in the environment that has sugar that is because yeast uses sugar as an energy sources naturally which will make the yeast generate more. The yeast could be identical in all the environments but most likely the situation will be that the yeast grows rapidly in the sugar.

This hypothesis needs to be tested and in order to do that their needs to be an amount of yeast from different environments collected analyzed and then have the data provided. The data was tested in four different environments and observed for 0,24, 48, 72, and 96 hour intervals. The environmental conditions used were a controlled environment, limited reproduction environment, additional food environment and introduced predation environment.


These materials are needed to complete the experiment:

4 – Yeast packets

1 – Ammonia mixture

1 – Sugar mixture

1 – Distilled water

1 – Balance

1 – Microbe Mixture

1 – Eyedropper

1 – Microscope

4 – 10mL graduated cylinder

4 – 18mm x 150 mm culture tuber

1 – Test tube rack


The steps were taken to conduct the experiment:

First the test tubes need to be labels with all the different materials that will be mixed into the yeast. The four labels will be Control, Ammonia, Sugar and Microbe. The lab data sheet will also have the names of each tube with the time and concentration of each solution so that all the data can be recorded.

Second the tube will be filled with the solution up to 10 ml of the solution.

Third the yeast suspension will be mixed in a separate container and will add drops of this solution to the each tube.

Fourth take out a drop of each solution from a tube and observe it under a microscope. The results will be documented on the data sheet and this step will be repeated in each time interval of 24, 48, 72 and 96 hours.

Fifth the lab needs to be cleaned up and have everything put back and record all the data and look over the results.


Once the experiment was conducted and all the data was recorded the data had to be analyzed. The hypothesis that was predicted was found to be correct. The yeast in the solutions tubes did become active; the yeast tube with the sugar was the tube that became the most active. In all the tubes the yeast physically expanded the tube with the sugar physically expanded to twice the size of the other tubes. This made the solution rise to the edge of the test tube. The yeast and sugar solution grew to more then 200 the count level and the other solution only exceeded the 100-count level. The data graph below shows that the solution had a constant rise and shows the population peaks and declines due to the reproduction rate. The yeast solutions eventually begin to die off.

Intervals | Control | Limited reproduction | Additional Food | Introduced Predation |

1 (0 hours) | 5 | 6 | 6 | 6 |

2 (24 hours) | 13 | 11 | 12 | 12 |

3 (48 hours) | 94 | 64 | 167 | 79 |

4 (72 hours) | 77 | 43 | 202 | 37 |

5 (96 hours) | 25 | 7 | 96 | 11 |


The lab had many stages and at each stage something different was occurring, at the beginning of the experiment the population growth cycle was slow and steady for all of the test solutions. At the end of the 24-hour period and beginning of the next 24-hour period the rate of growth increased considerably. The third day showed that the rate of growth was still increasing, but when it came to the next 24 hours everything changed at instead of in the increase you start to notice the rate of growth started to end and the yeast start to die off. The yeast solution observed is correlated to the simple organisms that are shown on a larger scale. The correlation between he simple organism and the more complex organism such as the waste of fresh water the more we tend to use it and waste the less likely will have enough later and will eventually run out.

The biogeochemical cycle monitors how yeast can be important in this aspect of this exchange. Two different manners can contribute to yeast fermentation and aerobic respiration. The difference between the 2 is the fermentation lacks oxygen in the formula, which results in only 2 ATP being produced. The fermentation process ifs done when the glucose molecule has 6 carbon atoms and is split into 2 molecules with 3 carbon atoms. When this happens it is called glycolysis and during this process and total of 10 chemicals react and will result in the release energy in the form of 2 ATP molecules. The aerobic respiration process occurs when oxygen is present and the same 10 steps of glycolysis happen. The oxygen that is added lets the glycolysis is an extra step that happens when the glucose molecule is completely taken apart. The release of energy from this process is larger and greater then the process of fermentation which is about 36 ATP molecules for each glucose molecule.

The aerobic respiration for fermentation process of yeast can produce energy from sugar. The aerobic resperation of oxygen must be present. The chemical formula is . When the oxygen is available the yeast can use the process of fermentation. The process will still use sugar since there is no oxygen the chemical formula will change to . Each of the formulas are similar because both produce ATo and .


The original hypothesis that was given for this lab was accurate and that was that the sugar solution that was combined with the yeast was the most active of all the 4 solutions used. Through out the process of this lab there were no problems and no errors happened during the process of this lab. The most important part to this lab was to make sure that everything was recorded correctly and accurately. Future lab experiments involving yeast and the release of oxygen provide a measurement of the biogeochemical cycle. The experiment had 2 sets of solution and would be used, 1 with oxygen for fermentation and one with for aerobic respiration.


Smith, T. M., & Smith, R. L. (2009). Elements of ecology (7th ed.).San Francisco, CA: Benjamin Cummings/Pearson.

UOP (2014). Yeast Lab Spreadsheet BIO/315 Version 2. Retrieved from University of Phoenix

UOP (2014). Yeast Lab Worksheet BIO/315 Version 2. Retrieved from University of Phoenix

UOP (2014). Lab Report Outline BIO/315 Version 2. Retrieved from University of Phoenix