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The objective of this experiment is to emphasize the influence that limiting factors have on a population. This lab tests yeast, a common component in baking, against two environmental factors (changes in temperature or concentration) to see what effect these have on the population dynamics of the yeast over a period of 72 hours.
There are two sections of tests included in this experiment: biotic and abiotic factors. The abiotic factor being tested here is what effect the temperature of the yeast’s environment has on its ability or inability to reproduce efficiently.
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The lab tests the yeast in three separate temperature settings: a cold temperature (4ᵒC), room temperature (22ᵒC), and a hot temperature (30ᵒC).
Here, the independent variable is the temperature of the yeast habitat and the dependent variable is the amount (in mL) of CO2 gas produced by the yeast. The biotic factor in this experiment is what effect the concentration of the yeast has on its ability or inability to reproduce efficiently. The lab tests three different concentrations of the yeast: add 0.25 mL, 0.5 mL, or 1 mL of yeast suspension to the test tube. The independent variable is the amount of yeast concentration added and the dependent variable is the amount (in mL) of CO2 gas produced by the yeast.
Yeast is a single-cell fungus that produces carbon dioxide (CO2) as a byproduct of cellular respiration. Therefore, the more yeast cells in an area, the more CO2 they will be able to produce. Yeast has many uses as a common ingredient in many foods and drinks, such as alcoholic beverages like beer and wine, and acts as a leavening agent in baking cakes, bread, and other foods by converting the fermentable sugars in the food into CO2. This is what makes the dough in many foods rise while baking.
This lab closely monitors a yeast population over a period of 72 hours, with various limiting factors being applied to the yeast population.
These are factors that have the potential to greatly influence a population’s dynamics, sometimes positively and sometimes negatively. They are generally categorized into two groups: biotic and abiotic. Biotic factors pertain to life or living things, and some examples in an environment include predators that can kill or injure an animal of a species, competitors that make it more difficult for one animal to access vital resources like food and water, and pathogens or parasites that can quickly kill or weaken a species.
In most cases, the existence of predators is a good thing because it helps to keep the population from becoming unbalanced with the coexisting species living around them. However, if the predator population becomes too large, or if an abundance of new predators is introduced to the area, the population of this species will quickly decrease, and possibly be endangered or, after many years, extinct. In addition, having competition in an environment is important to keeping to well-balanced between plants and animals, but can backfire when there is too much competition, and plant life becomes scarce, unable to support the animals. This is true with all limiting factors: they can have a good or bad impact on a population.
On the contrary, abiotic factors pertain to non-living things, like sunlight, climate, temperature, and varying amounts of rainfall. For example, rainfall is essential in an ecosystem to hydrate both animal and plant life, and it is necessary for survival. However, too much rainfall at one period of time, or flooding, can wash away and kill many forms of plant life, damaging the populations that rely on plants for food, in turn. In addition, temperature can impact a population like yeast (which is tested in this experiment) positively or negatively.
For example, if the yeast’s environment is very warm, the yeast will be able to thrive in it. This is due to its activation in warmer temperatures. It is able to reproduce faster and more efficiently in a warm environment, thus producing more CO2. However, when placed in colder temperatures, it deactivates and, although it does not die or stop producing CO2, this drastically slows down the rate of reproduction and production of CO2. Therefore, these factors (both biotic and abiotic) can potentially, given the circumstances, greatly impact the dynamics of a population. This lab’s goal is to demonstrate these effects on yeast populations.
Yeast is the most efficient model to demonstrate these population dynamics because it can easily be closely watched and it is a simple organism. Testing multicellular organisms in a lab can be more challenging because many of them possess some sort of rational thinking method that can impact the results in a lab. Yeast is a simple, unicellular organism that has only two intentions in its life: survive and reproduce. This eliminates any impact that yeast’s intelligence could have on the experiment. This is one less control that needs to be worried about. Also, yeast’s reproduction is rapid.
If the lab were to test a multicellular organism, it would take weeks or even months to get a proper result. Using yeast, the lab only took 72 hours. Furthermore, collecting CO2 from the yeast is a viable method for determining the population growth of yeast because CO2 is a byproduct of the yeast’s cellular respiration process. As more yeast cells are produced, more CO2 will be produced because there will be more cells to produce the gas in the enclosed environment as they respire, as measured through the volume displacement method.
A carrying capacity in a population is “the maximum number of individuals of a given species that an area’s resources can sustain indefinitely without significantly depleting or degrading those resources” (“Population Size”). Once the carrying capacity is reached or exceeded, this will take a toll on the environment as a whole. The resources that support this species would quickly diminish, and any other animals that this species preys on would become endangered because there are too many predators killing them. This is why a good balance of limiting factors needs to be maintained to evenly support an ecosystem as a whole.
This lab investigates these factors, applies them to a yeast population, and analyzes the results.
The following table summarizes the results of the experiment for different temperature settings:
| Time (hours) | Cold (4ᵒC) | Room (22ᵒC) | Hot (30ᵒC) |
|---|---|---|---|
| 0 | Initial Bubble Size (mL) | Initial Bubble Size (mL) | Initial Bubble Size (mL) |
| 24 | Bubble Size (mL) | Bubble Size (mL) | Bubble Size (mL) |
| 48 | Bubble Size (mL) | Bubble Size (mL) | Bubble Size (mL) |
| 72 | Bubble Size (mL) | Bubble Size (mL) | Bubble Size (mL) |
| Total CO2 Production (mL) | Total CO2 Production (mL) | Total CO2 Production (mL) | Total CO2 Production (mL) |
Graphs depicting the change in CO2 production over time for each temperature setting are shown below:
The following table summarizes the results of the experiment for different yeast concentrations:
| Time (hours) | 0.25 mL | 0.5 mL | 1 mL |
|---|---|---|---|
| 0 | Initial Bubble Size (mL) | Initial Bubble Size (mL) | Initial Bubble Size (mL) |
| 24 | Bubble Size (mL) | Bubble Size (mL) | Bubble Size (mL) |
| 48 | Bubble Size (mL) | Bubble Size (mL) | Bubble Size (mL) |
| 72 | Bubble Size (mL) | Bubble Size (mL) | Bubble Size (mL) |
| Total CO2 Production (mL) | Total CO2 Production (mL) | Total CO2 Production (mL) | Total CO2 Production (mL) |
Graphs illustrating the change in CO2 production over time for each yeast concentration are displayed below:
The results of this experiment indicate significant differences in CO2 production by yeast under varying temperature and concentration conditions.
When observing the effect of temperature on yeast population dynamics, it is evident that temperature plays a crucial role in yeast reproduction and CO2 production. As expected, yeast thrives in warmer environments (30ᵒC) and exhibits the highest CO2 production. This is due to the activation of yeast metabolism at higher temperatures, leading to increased reproduction rates.
Conversely, at lower temperatures (4ᵒC), yeast metabolism is significantly slowed, resulting in reduced CO2 production. While yeast remains viable in cold conditions, its reproductive capacity is limited, leading to a smaller yeast population and lower CO2 output.
At room temperature (22ᵒC), yeast demonstrates moderate CO2 production, reflecting its intermediate metabolic activity under these conditions. This aligns with the concept of temperature as a limiting factor that can either support or hinder a population's growth depending on the specific temperature range.
Overall, the results confirm that temperature is a critical abiotic factor affecting yeast population dynamics, with warmer temperatures favoring yeast growth and CO2 production.
Examining the influence of yeast concentration on CO2 production reveals that yeast population size directly correlates with the amount of yeast added to the environment. As yeast concentration increases (0.25 mL to 1 mL), CO2 production also increases proportionally.
At the lowest yeast concentration (0.25 mL), yeast cells are sparsely distributed, resulting in limited CO2 production. However, as more yeast cells are introduced (0.5 mL and 1 mL), CO2 production escalates significantly, indicating enhanced reproductive activity.
This outcome aligns with the principle of population growth being contingent on available resources. In this case, the yeast population's growth is constrained by its initial concentration. Higher concentrations provide yeast cells with more opportunities for reproduction, leading to increased CO2 production.
Several factors may have introduced limitations and sources of error into the experiment. These include variations in yeast suspension quality, fluctuations in temperature settings, and potential inconsistencies in mixing the yeast and molasses solution. Additionally, small air bubbles or leaks in the test tube seal could affect CO2 measurements. To minimize these sources of error, meticulous attention to procedure and equipment calibration is essential.
This experiment underscores the significant impact of environmental factors, specifically temperature and yeast concentration, on yeast population dynamics. Temperature, as an abiotic factor, influences yeast reproduction and CO2 production, with warmer temperatures promoting growth and higher CO2 output. Yeast concentration, a biotic factor, directly correlates with population size and CO2 production, demonstrating the importance of resource availability.
For future experiments, it is advisable to replicate these tests with more precise temperature control and yeast suspension consistency. Additionally, investigating the combined effects of temperature and yeast concentration on population dynamics could yield valuable insights into complex ecological interactions. Furthermore, exploring other abiotic and biotic factors, such as pH levels and nutrient availability, can contribute to a comprehensive understanding of population dynamics in various ecosystems.
How Environmental Factors Affect a Yeast Population’s Ability to Reproduce. (2016, Sep 27). Retrieved from https://studymoose.com/document/yeast-population-lab-report
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