24 January Science 8 Fermentation of sucrose by yeast

  1. Review DSN entry from previous class.
  2. Review information about fermentation from previous class http://rfrazier.msblogs.aes.ac.in/2018/01/22/22-january-science-8-reflection-on-carbon-presentations-reading-about-fermentation-respiration-metabolism/
  3. Prepare DSN entry for today’s class.
  4. We will set up yeast fermentation of sucrose in a warm water solution. Here is a very simple procedure: http://www2.mrc-lmb.cam.ac.uk/microscopes4schools/yeast.php
  5. Try 2 methods for observing the bubbling–bottle with a balloon and flask with a gas delivery tube and a test-tube with limewater (an indicator of carbon dioxide).
  6. The temperature to “activate” yeast is important. See these temp. ranges reported from the Exploratorium. Which should you use? Why?: https://www.exploratorium.edu/cooking/bread/yeast_temp.html
  7. Once your fermentation set-ups are bubbling along. Put a drop of the solution (try to avoid any of the solid material) on a slide and cover with a coverslip. Wipe off excess liquid on the slide (outside of the coverslip) before placing it on the microscope. Focus on low power, then move to the middle power (what is the magnification?). Check with Dr. F before moving to highest power. Watch the yeast cells. You may see some in the process of dividing–called budding. Sketch what you see. Try to take photos. The ipad stands can make this easier. You may need to adjust the light on your microscope. Also try to add a stain–iodine or methylene blue (not both at the same time). The stains may be taken up by structures within the yeast cells.
  8. An important thing to think about is how all life is based on cells and that the incredible chains of chemical reactions that characterize life take place within cells in the various organelles. Energy transformation occur in the mitochondria–and when we look at green plants next, the “capturing” of the sun’s energy in the bonds of certain molecules in chloroplasts. The nucleus of the cell is where the genetic information resides in the form of DNA. The process of reproduction involves copying the DNA and the dividing. Various segments of DNA are codes for the cells to make certain molecules. Other segments are a little like switches that turn on and turn off the action of molecule making segments. Again, just contemplate the incredible sets of reactions that make life what it is from a cell, to an organism, to an ecosystem, to the entire earth.
  9. Use the ball and stick molecular models to simulate the reactions that take sucrose to ethanol and carbon dioxide during anaerobic fermentation by yeast. (Remember the conservation of mass AND the idea that each reaction will involve the simplest steps.)
  10. To further strengthen your appreciation for the significance of cells, read another chapter from Lives of a Cell by Lewis Thomas:

Micrograph taken by 8th grader with Ipad of yeast cells (stained with methylene blue).

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