Culturing Yeast: Baking Bread in Biology

Loves of bread.

Nice and fluffy loaves of bread requires the generation of bubbles in the dough. This is typically done either with an acid-base reaction (baking soda and an acid) or with yeast. Since we’re doing biology, we made some loaves and focused on how the process of bread making require careful management of the environment for the yeast to produce the carbon dioxide gas that makes the bubbles that makes the bread rise.

We followed the bread-baking recipe I’ve used before for the middle school’s student-run business, but had to shorten rising times to get it all done by the end of our class.

Yeast is a single-celled fungi (typically Saccharomyces cerevisiae). Fungi are heterotrophs, so focusing on what the yeast requires for life and metabolic activity requires consideration of:

  • water (moisture)
  • warmth (but not too warm)
  • energy source (short chained carbohydrates to make the energy more easily accessible)

Yeast produces carbon dioxide bubbles via fermentation (Styurf et al., 2017). It could do it through respiration, but in the bread dough there is not a lot of oxygen available (more info on respiration here).

Fermentation looks something like:

C6H12O6 → 2 C2H5OH + 2 CO2

So, the carbohydrate (glucose) is converted to ethanol and carbon dioxide.

As opposed to respiration (which requires oxygen):

C6H12O6 + 6 O2 → 6 H2O + 6 CO2

Yeast fermenting/proofing.

Video: From a Single Cell to an Alpine Newt

Becoming from Aeon Video on Vimeo.

Watch a single cell become a complete organism in six pulsing minutes of timelapse. A film by Jan van IJken (www.janvanijken.com).

More on this video: aeon.co/videos/watch-a-single-cell-become-a-complete-organism-in-six-pulsing-minutes-of-timelapse
Watch more on Aeon: aeon.co/video
Subscribe: vimeo.com/aeonvideo

An exceptional timelapse of the developing of an Alpine newt by Jan van IJken

John Snow: How to be a Scientist

These three excellent, short videos on John Snow’s life and work on cholera do a nice job of describing what makes for good science–careful observation; good notes; creative analysis of data, etc. They should make a good “spark your imagination” introduction to biological science.

They also have an excellent explanation of all the ‘lies’ and liberties they took in the making of the video.

Glossary of Plant Description

From: The vPlants Project. vPlants: A Virtual Herbarium of the Chicago Region. http://www.vplants.org
From: The vPlants Project. vPlants: A Virtual Herbarium of the Chicago Region. http://www.vplants.org

The vPlants Project. vPlants: A Virtual Herbarium of the Chicago Region. http://www.vplants.org is a wonderfully comprehesive collection of pictures with plant descriptions: plant form; leaf shapes; stem and leaf patterns; flower shapes; and more.

Chickens 911

Initial reports indicated a chicken with a broken leg; some rumors suggested the chicken had gone missing as well. These reports instigated an investigation by the Chicken Committee. They determined that the chicken was there, but something was wrong. They sent out a call for medical assistance.

X-ray of our chicken.
X-ray of our chicken.

Help came in the form of Dr. Emily Leonard from the Cherry Hills Veterinary Hospital (who happens to be a mom at our school). She took the chicken in for examination.

Based on the X-ray, there were no bones broken, so the issue must have been something else. The large egg that showed up on the radiograph suggested that the chicken could have been egg-bound, however, 20 minutes later, the chicken laid the egg.

So, the chicken is still under observation.

After the initial examination, Dr. Leonard brought the chicken back to school. It needed to be isolated and observed–which is something we now know to do in the future in any other case of injury–and the head of the Chicken Committee (the Chicken Head) made the call that the animal should go back to the hospital for the weekend.

Dr. Leonard deals mostly with pets, so she had to do quite a bit of research. “I learned a lot about chickens today,” she told me afterwards. This is a message I hope the students internalize. With the ready access to information we have today, it’s not so much about the facts you have memorized, but more about having the flexibility and ability to deal with new challenges by doing research and then applying what you learn are essential skills.

Dr. Leonard takes the chicken in for observation.
Dr. Leonard takes the chicken in for observation.