12.1: Instructor Guidelines
- Page ID
- 118021
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Purpose
Students are introduced to aerobic cellular respiration and fermentation during this lab. Cellular respiration will be monitored through the presence of carbon dioxide in solution and subsequent changes in pH, as well as redox reactions. Fermentation levels will be monitored through the production of CO2 gas. Students will learn how to use pH indicators and saccharometers to measure CO2 production.
Tasks
Students will complete the following during this lab:
- Investigate cellular respiration in dormant versus germinating seeds through the production of CO2 (acid) and subsequence change in pH.
- Use methylene blue and microscopy to detect the presence or absence of redox reactions that occur during aerobic cellular respiration.
- Use saccharometers to measure CO2 levels produced through alcoholic fermentation in yeast.
Lab instructors should provide students with an introduction to cellular respiration and fermentation. Although the material is also covered in the lecture and course textbook, these two topics tend to be some of the most challenging for all biology students. Instructors may want to provide students with a brief overview of glycolyis, the Kreb's cycle, and the electron transport chain for aerobic cellular respiration. Students may not know that some bacteria undergo anaerobic respiration with a final electron acceptor that is not oxygen. Remind students that fermentation is different from anaerobic cellular respiration.
Exercise A requires preparation of the pea plant seeds at least two days prior to the experiment, which may be completed by the students or the laboratory technicians. Additionally, the lab manual asks students to record color changes after 24 hours. This is not possible for our students, so instructors may ask a colleague or the lab technicians to take a picture of the samples after 24 hours if desired. According to our previous results, there are no differences between the three tubes after 2 hours vs. after 24 hours.
In Exercise B, remind students that the yeast cells should be viewed under 400x or 1000x (oil immersion) total magnification.
There are a total of four exercises listed for this lab (Exercises A-D), but currently, our laboratory supplies are insufficient and we only have enough materials and saccharometers to complete Exercises A-C. In Exercise C, each group of students should be assigned two conditions to test (see Table 3 in the lab manual for Exercise 12):
- Sacch 1 (no yeast) and Sacch 3 (less yeast), or
- Sacch 2 (no glucose) and Sacch 4 (more yeast).
Students will need to be introduced to the saccharometers and how to properly fill each with the yeast/glucose mixture, especially Procedure Step 5 of Exercise C. Once each saccharometer has been properly filled, they should be taped to the tray or lab benchtop in order to prevent shattering of the glass should they fall over.