Yeast are facultative anaerobes, which means that they are capable of performing both aerobic and anaerobic respiration depending on their environmental conditions. A team of biology students reads that the alcoholic fermentation of yeast produces bubbles of carbon dioxide which cause bread to rise while baking. The students want to measure the rate of carbon dioxide production by a sample of yeast in a large test tube in their high school laboratory. They are able to insert a digital CO2 sensor into the test tube. The sensor is connected to a computer, enabling the students to record their data automatically. They plan to take readings every 30 seconds for an hour.

Question

What is one important parameter that the students must consider when developing their procedure to get accurate results?
Responses

The students must add a photosynthetic organism, like algae, to the sample of yeast.
The students must add a photosynthetic organism, like algae, to the sample of yeast.

The students must be careful to keep yeast in the dark and never exposed to direct sunlight.
The students must be careful to keep yeast in the dark and never exposed to direct sunlight.

The students must be certain that there is little to no oxygen present in the test tube.
The students must be certain that there is little to no oxygen present in the test tube.

The students must ensure that the test tube is exposed to direct sunlight.

Answer 1

The students must be certain that there is little to no oxygen present in the test tube.

Since yeast are facultative anaerobes, they can perform fermentation (anaerobic respiration) in the absence of oxygen, leading to carbon dioxide production. If there is significant oxygen present, the yeast may switch to aerobic respiration, which does not produce carbon dioxide in the same way as fermentation does. Hence, to accurately measure the rate of carbon dioxide production from alcoholic fermentation, minimizing oxygen levels is crucial.