31 January Science 8 Yeast Fermentation

Mindful moment–take your mindful moment today while watching the yeast fermentation. Do you know of Greta Thunberg? This is a young person speaking “truth to power.” Watch the video at the commondreams.org link. Do you think she speaks for you?

Review the previous class–blogpost and your DSN.

Prepare your DSN.

In your carbon presentation group, set up the two yeast fermentation demonstrations/experiments (see below). Make sure everyone in the group is involved in the procedures and the observations. Ask each other about your understanding of fermentation as described in the blog notes. Raise and discuss questions. Discussion and participation should be distributed across the group. Do your part. Hold up your end. Contribute to the good of the group. Be inclusive.

Submit any questions with your name included on a notecard. Questions of general interest will be address to the whole group. Other questions will be addressed individually. Please do not say you don’t understand something if you have never asked a question. It is your right and your responsibility to bring up ideas that are puzzling, confusing, difficult. It is highly probable that your questions is deep, important, and meaningful.

  • What are yeast? See links below. Yeast are fungi. They are one-celled organisms that are essential to making bread, beer, wine. Some say that yeast were the first living organisms domesticated by humans. Yeast are also an important model organism for scientific research. Yeast reproduce by cell division called budding. Think about how a yeast population will grow. Do the math! What happens when the yeast have consumed all the sucrose? What are the products of anaerobic fermentation of sucrose by yeast? As the concentration of the products build up, as the yeast population grows exponentially, as the food source depletes, what happens to the yeast? Yeast can carry out respiration with oxygen (aerobic) or without oxygen (anaerobic) depending to environmental conditions.
  • Micrograph taken by 8th grader with Ipad of yeast cells (stained with methylene blue).


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

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).

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

See drawings on board:

 Make sure all containers are clean. Chemical contaminates could affect the growth of the yeast.

Make up a solution of 120 grams of sugar (sucrose) in 300 ml water at 40 degrees Celcius. Add 1/2 package of dry activated yeast. Put 200 ml. of this solution in the bottle. Put the remaining solution in the flask.  Stir and attach a balloon to the bottle and a stopper and tube to the flask. Fill the smaller flask 1/2 way with limewater and cover the limewater with a very thin layer of oil (to make a barrier with the atmosphere).

Note: Limewater is an indicator of carbon dioxide. (Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)) (aq means aqueous or dissolved, g means gas, s means solid, l means liquid)

Observe. Watch the time and see what changes take place. Look at the rate of bubbles. Look at the volume of the balloon. How do you think yeast reproduce? How do you think the rate of reproduction relates to the rate of fermentation or rate of the overall reaction changing sugar to ethanol and carbon dioxide?

When ready, we will take off the balloon and put a drop of solution on  a slide. Cover the drop with a coverslip. Examine under low power first. Then examine under medium power. Try to stain a drop of the solution. Sketch some sample yeast cells. Every living thing is made of cells. The transformations of matter and energy take place the cells of living things. Think of the magnitude of living cells on the earth and how the cumulative activity affects the chemistry of the earth.

  • * * * * *

Checklist–how are you doing so far this semester:

  • Annotated bibliography complete to date.
  • Add a reference to your annotated bibliography from links on today’s blog related to human impact on the environment.
  • DSN. How many classes have we had to this date? How many entries do you have? How many are complete (all 7 items)? Work on any incomplete entries.
  • Carbon essay.
  • What are your big understanding so far? What are your main questions? What ideas seem to be bridges to future learning? What ideas look like they might be barriers to future understanding? Give examples.
  • Carbon cycle presentation–is your group’s presentation uploaded to this year’s folder (see previous blog for link.)?
  • Is your list of partners and projects complete and up to date? Are you keeping records of useful collaboration experiences? What make a collaboration better than working alone? How can collaboration in diverse groups prepare you for future life/work experiences? How do you see your own roles, responsibilities, contributions, experiences?


  • * * * * *

Information from previous blog:

Life is based on cells. Inside the living cell, “food” is used as fuel or building material through complex series of chemical reactions. These reaction break bonds in molecules–harvesting the energy and make bonds building up a huge array of molecules used in growth, development, reproduction, and all life processes.

Read the conclusion from: Cell Energy and Cell Functions


“Cells need energy to accomplish the tasks of life. Beginning with energy sources obtained from their environment in the form of sunlight and organic food molecules, eukaryotic cells make energy-rich molecules like ATP and NADH via energy pathways including photosynthesis, glycolysis, the citric acid cycle, and oxidative phosphorylation. Any excess energy is then stored in larger, energy-rich molecules such as polysaccharides (starch and glycogen) and lipids.”

Cellular respiration is the name for a series of reactions where the cell uses the energy from food.


Fermentation is respiration without oxygen or anaerobic respiration. (See notes in link above).

Metabolism is the term referring to all the reactions (both breaking molecules down and building them up) that make up the processes of living.

  • * * * *

In order to gain some experience observing respiration, we will set up some situations where yeast ( a living organism–a fungus) uses sucrose (a carbon compound produced by plants through photosynthesis) to live. We will observe some of the changes that take place in a sucrose solution to which a living yeast culture has been added. We will observe the yeast after the population has grown with the microscope.

We have talked some about how food is both fuel and building material. In our study of matter, we looked at the conservation of mass. This meant taking the atoms at the beginning of a reaction and seeing how they are transformed into products at the end of the reaction. Every living thing takes in matter and gives out matter in a different form. In the process energy is also transformed. See the scientific claim below about how a molecule whose bonds store energy is used by yeast and is then transformed into products which are expelled from the cell. The claim is stated in the two-step reaction equations. Of course, you need to pay close attention to the reaction equations.

  • Sucrose is converted to 2 molecules of glucose/fructose.
  • 1st step C12H22O11 + H2O + invertase → 2 C6H12O6

  • (below 2 ways of picturing sucrose–a 12 carbon sugar; sucrose is table sugar)

Glucose/fructose is converted to 2 molecules of ethanol and 2 molecules of carbon dioxide.

  • 2nd step C6H12O6 → 2 C2H5OH + 2 CO2  

  • (below a diagram of glucose, fructose, and ethanol) (Can you see how the glucose and fructose can be transformed into ethanol with a release of carbon dioxide?)








See the following link to *Lives of a cell* by Lewis Thomas. This is a significant example of science writing for the general (educated) public. Pick out one of the chapters to read. Be prepared to share your reading through an annotation: description, summary, assessment, reaction.



 * * * * *

Read and listen to the following. Add to your annotated list of references.

How social media is inspiring children to save the natural world


The History of Wastefulness

Waste. Trash. Rubbish.

Whatever you call it, there’s no escaping it.

The world now throws away over two billion tonnes of waste every year. Unless we see drastic change, it’s predicted that by 2100, we’ll be producing three times as much rubbish as we’re doing today.

Australian journalist Alexandra Spring is fascinated by this history of wastefulness, and how our relationship with rubbish has evolved over time.

Across three episodes, she’ll discover how our current battle with rubbish has been shaped by our wasteful past and what we can learn from previous ages to inform a better future.

Image: Alexandra Spring looks up at bales of plastic recycling in San Francisco (Credit: Audio Always)




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