Holy Bread
Age
Elementary School (Observation),Middle School (Hands On),High School (Hands On)
Format
Stage Show (elementary), Hands-on (middle and high school)
Materials
Piece of White Bread Active dry yeast (can be purchased in packets – keep in fridge for storage) Sugar Warm water CO2 trap – 160 ml serum bottle with seal , glass adaptor, tubing Bromothymol blue Beaker with warm water Hot plate Thermometer 250 ml Erlenmeyer flask – WITH the stopper that HAS a hole in it for the straw to fit through it!!! Drinking straws If possible: Table microscope, glass slide – to show yeast
Safety Precautions
Science Theatre demonstrators must keep the safety of themselves and their audience in mind at all times. All Science Theatre demonstrators must have read through the Safety Training page. The ST Safety Box with first aid kit, fire extinguisher, etc. should always be available to demonstrators. Always wear safety gloves, glasses, and a labcoat if handling chemicals; always perform potentially dangerous demonstrations at a safe distance from the audience; and always keep a very close eye on any volunteers you call from the audience.
Demonstrators should wear goggles and lab coats, and the ST general safety box should be available to them.
Although almost absolutely impossible – if your yeast is somehow supercharged and produces litres of carbon dioxide, the CO2 trap could explode. More likely, the stopper will just pop off. Even more likely, the yeast will just bubble nicely like they’re supposed to - but keep those goggles on, just to be sure!
Wear gloves and a lab coat when using the bromthymol blue, although not harmful, we want to set a good example, and it may stain your skin or clothing.
Only demonstrators should be allowed near the hot plate.
Preparation
-Prepare bromthymol blue solution ahead of time [0.1 g Bromothymol blue dye in 500 ml water(0.02%). Should be blue-green in color]. A red cabbage indicator dye would also work in this demonstration, if you care to substitute.
-Prepare a slide of active yeast, set up microscope
-Put indicator solution into the gas receiving vessel and into the 250 ml Erlenmeyer flask, enough that it is visibly blue green (may be different color depending on the acidity of your tap water!)
NOTE: If your tap water has a lot of dissolved minerals, or dissolved CO2, it may already be yellow – this is bad. Add a drop of NaOH to bring the pH back up so the bromthymol blue looks blue-green again. This way, the students get the full effect of starting at neutral, and with the addition of carbonic acid it turns yellow. We scientists can be tricky!
Demonstration
Warm a beaker of water on the hotplate to about 40 degrees Celsius .
Pour 1 tsp yeast and tsp table sugar into the serum bottle.
Mix by swirling
Insert the stopper with tubing attachment
Put the side of the container with the yeast in it into the beaker with the warm water.
Put other end of tubing into the erlenmeyer with the bromthymol blue + water mixture, let sit. (See diagram)
Start your script (it takes a while for the yeast to become activated) – see below
What to Say
-Hold up a piece of bread. Ask if anyone has ever noticed just how “holy” it is?
-What do we think made these holes? Actually, a little tiny microorganism made these holes. Lets find out how.
-What do we breathe in and out? (in = Oxygen, out= Carbon Dioxide). This is the same for all animals. And although yeast aren’t animals – they are fungi, they still breathe like you and I.
-(pick up the erlenmeyer flask and blow bubbles, changing the color from blue green to yellow. OR have a volunteer from the class do it.)
- Explain – when we exhale, we breathe out carbon dioxide. The carbon dioxide in our breath combines chemically with the water in this beaker to form carbonic acid. And remember, we added indicator - a kind of dye that changes color in the presence of an acid, turning yellow.
-So now, lets look at our experiment. Yeast are revived by adding sugar (food) and heat. Then they begin to grow. The carbon dioxide produced by the yeast turns the solution yellow.
- Let the kids look through the microscope. See if you can find any cells budding. Budding is a type of reproduction, except it happens very quickly. Because they can reproduce so quickly, they use a lot more food than you or I.
Why It Is
Saccharomyces cerevisae is the scientific name for yeast. Most bakers are extremely familiar with this household fungus! Yeast is a single-celled organism, whereas you and I are composed of billions of cells of hundreds of different types. We buy this fungus at the grocery aisle, and it looks like this (show a spoonful). All organisms need the proper conditions – warmth and food, so we’ve provided our yeast with sugar and 40 degrees C (about 105 degrees F).
Just like humans and other animals, yeast breathe in oxygen and breathe out carbon dioxide. This point is first demonstrated by blowing through a straw into indicator solution located in the Erlenmeyer flask. The indicator solution will turn from blue-green to light green to yellow due to the formation of carbonic acid when carbon dioxide goes into solution. A chemical reaction takes place in the receiving flask as a result of the yeast “breathing” just like we do, releasing carbon dioxide. We’ve trapped the gas, and it will travel through the tubing into the other chamber. Over the next 10 to 15 minutes, gas bubbles will emerge in the pH indicator solution. The solution will change color from blue-green to yellow-orange as carbon dioxide produced by the yeast dissolves in the water to make carbonic acid.
Yeast are just one of the billions of microorganisms that we employ every day in ways to keep our lives running smoothly. Whether we realize it or not, we are dependent on the bacteria in our intestines to digest our food, the fungi in our mucous membranes to keep out invading pathogens, and billions of other uses that we rarely think of. It is our duty to preserve the micro on behalf of the macro.
Think about it. All of this, just from a piece of bread!
Real Life Examples
Scientists use microorganisms all the time in tasty ways, besides engineering holes in bread:
-Special types of bacteria are used to make yogurt
-Other types of bacteria are used to turn milk into cheese (yum!)
-Lots of research is being done on using bacteria and fungi to eat sewage and clean up sludge
-symbiotic microorganism in the stomachs of cows, deer, sheep, etc (called RUMINANTS) help them digest all of the plants that they eat. We don’t have those things in our stomachs, so we can’t go around eating hay!
-ditto for termites muuuuuuuuch much more!