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Microbe–Factor–Process Research

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Microbe–Factor–Process Research

Use the evidence dossier below to investigate how temperature affects a microorganism’s life process. Read the passage and data, then answer every question. Treat the data as results from a controlled classroom investigation; no outside sources are needed.

Evidence dossier: yeast and respiration

Yeast is a single-celled fungus. Baker’s yeast (Saccharomyces cerevisiae) obtains sugars from its surroundings. When oxygen is scarce, it can release energy by anaerobic respiration: glucose is converted into ethanol and carbon dioxide. This process is called fermentation. Carbon dioxide gas can be collected and measured; a faster rate of gas production is evidence of a faster rate of fermentation, although it is not a direct measurement of all energy released. A class tested the effect of temperature. Each flask contained the same volume of warm water, the same mass of dried yeast, and the same concentration and volume of glucose solution. The flasks were kept at different temperatures. After a short settling period, the class measured the volume of carbon dioxide produced in five minutes. The flasks were otherwise treated alike. The data are shown below. In this investigation, temperature is the abiotic factor, yeast is the microorganism, and anaerobic respiration (fermentation) is the life process. The results describe this particular setup; they do not prove that every yeast strain or every condition will give identical results.

Temperature (°C)

CO₂ produced (mL)

Interpret the evidence

Use the evidence dossier and class results to support your answers. When a question asks you to explain, connect the factor, the microorganism and the process.

1.In this investigation, identify the microorganism, the abiotic factor, and the life process being studied.

2.Which statement best describes the role of carbon dioxide in this investigation?

It is a nutrient that yeast absorbs to make glucose.
It is a product of fermentation used as an indicator of the process’s rate.
It is the abiotic factor being changed.
It measures the temperature inside each flask.

3.Calculate the increase in carbon dioxide produced between 15°C and 35°C. Include the correct unit.

4.Describe the pattern in the results as temperature rises from 15°C to 35°C. Use at least two values from the table.

5.True or false? The results show that the yeast produced carbon dioxide fastest at 35°C among the three temperatures tested.

True
False

6.Complete the cause-and-effect chain using the investigation: Higher temperature (within the tested range) → → more produced in five minutes.

7.Why did the class keep the amounts of yeast, glucose solution and water the same in each flask?

8.Match each term to its meaning in this investigation.

Independent variable
Dependent variable
Control variable

Carbon dioxide volume measured after five minutes
Amount of glucose solution kept the same
Temperature changed between flasks

9.Explain why the table supports the claim that temperature affected fermentation in this setup. Include the trend and the link between carbon dioxide and fermentation.

10.A student concludes, “Yeast fermentation will keep getting faster at any temperature above 35°C.” Is that conclusion justified by these results? Explain one limitation and suggest one improvement or follow-up test.